Tires can help save gas

Don't overlook your tires when it comes to saving fuel. Underinflated tires, for instance, require more energy to roll along, which eats up more gasoline. They also cause a tire to wear more quickly.

Use a tire gauge at least once a month to keep them inflated at the vehicle manufacturer’s recommended pressure. That figure is typically found on a placard on the driver’s door jamb, but check your owner's manual for the location on your car and for the proper procedure. Don’t go by the maximum inflation pressure embossed on the tire's sidewall.

When buying replacement tires, look for a model with low rolling resistance—basically a measure of how easy it is for a tire to roll down the road. Consumer Reports measures and rates the rolling resistance of every tire we test, except for winter tires. Our tests show a 1- to 2-mpg difference in rolling resistance between the best and worst replacement tires. (Watch the video on how we test tires.)

Don't let rolling resistance be your only criterion for choosing a tire, however. On some tires, lower rolling resistance can compromise all-weather grip and braking or cornering capabilities. We recommend you select the model that provides the best overall performance for your needs, and then consider rolling resistance as a tie-breaker.

Choosing the right tires and maintaining them at the proper pressure can save you about $100 a year at today's gas prices.

See our Ratings of car, truck, and winter tires and find the best one for your vehicle. Plus, see how we test tires.

Car, SUV, and tire recalls

There have been a few significant recalls announced in the past few weeks affecting Dodge, Land Rover, Mercedes-Benz, and Volkswagen, plus a Toyota safety enhancement and a recall on tire valve stems. If your vehicle is listed here, you will be contacted by the manufacturer with the information on what you need to do or we provide a number to contact yourself. However, the valve stem recall requires action on the owner’s part.

2009 Dodge Journey

Chrysler is recalling almost 6,700 Dodge Journey SUVs equipped with a 3.5-liter engine due to a problem with the engine wiring harness that could contact the left transaxle mount and cause an engine fire.

Dealers will inspect the engine wiring harness for damage and repair to secure the harness away from the left transaxle mount.

Chrysler has yet to announce when owners will be notified. In the meantime, owners can call Chrysler at 1-800-853-1403.

2005-2006 Land Rover LR3 and Range Rover Sport

Land Rover is recalling over 37,000 LR3 and Range Rover Sport vehicles. The relative motion between the steering wheel hub and/or steering column cowl with the clockspring, which contains air bag circuitry, could cause a fracture in the driver-side air bag wiring connection. The SRS warning light will illuminate to alert the driver that a repair is necessary, but if a driver ignores the light and gets into a crash, the air bag may not deploy properly.

Dealers will make the necessary repairs to fix the alignment. The recall is expected to begin around July 21st. Owners may contact Land Rover at 1-800-637-6837.

2006-2008 Mercedes-Benz GL & ML class

Mercedes-Benz is recalling over 52,000 GL and ML class vehicles equipped with the Flex-N-Gate trailer hitch. Some of the seams connecting the hitch to the attachment bar used to connect it to the body frame do not meet specifications and may result in the hitch separating from the attachment bar.

Dealers will repair the trailer hitch and owners are urged not to use the hitch until it is repaired. Owners may contact Mercedes-Benz at 1-800-367-6372.

2008 Volkswagen Passat & 2009 Volkswagen Tiguan

Volkswagen is recalling over 4,000 Volkswagen Passat and 2,500 Tiguan vehicles equipped with 2.0T FSI ULEV II engines. The problem occurs when the engine is in idle and the air conditioning is turned on, the software may not control engine idle. As a result, the engine could surge unexpectedly.

Dealers will inspect and update the engine control module that contains the software, free of charge.

The recall began at the end of May. Owners may contact Volkswagen at 1-800-893-5298.

2004-2006 Toyota Sienna

Toyota is conducting a safety improvement campaign on over 196,000 Toyota Sienna minivans equipped with power rear liftgate struts. The gas struts used to help lift the rear power liftgate could wear out earlier than expected and could eventually cause the liftgate to fall a few inches or completely close.

Dealers will replace the gas struts with new ones that have a longer life. Owners can contact Toyota at 1-888-270-9371.

Tech International tire valve stems

Tech International is recalling 6 million snap-in valve stems manufactured between July and November 2006. The rubber portion of the stem could crack and cause a loss of tire pressure, potentially leading to a crash.

Tech International will replace the valve systems and the tire if necessary. Owners may contact Tech International at 1-740-967-9015.

For more information about this recall, read the Safety blog’s report: "Warning issued on faulty tire valve stems following rollover death."

—Liza Barth

Toyota Sienna AWD run-flat tires: No worse for wear

Lots of tire life left based on our extended tread-life test.

We’ve had a series of blog reports on our Toyota Sienna following the tread life performance of its run-flat tires.  (See the links below.) Now, at just over 30,000 miles, (30,247 miles to be exact, as shown) we’re impressed with the wear performance of the tires, which are projected to wear out at no less than 54,000 miles—comparable or better than conventional all-season tires.   

For those of you just joining us, we purchased a new 2007 Toyota Sienna XLE AWD with the Dunlop SP Sport 4000 Self-Supporting Technology tires (DSST)—run-flat tires. After the road test was completed, we purchased a new set of Dunlop SP Sport 4000 DSST tires for a tread-life evaluation on our Sienna. The evaluation started at the end of March 2007 and now, one year later, the tires still are trucking on.

To be fair to the tires, we have been checking inflation pressures religiously; checking alignment, rotating the tires, and measuring the average tread depth in tread grooves (four grooves) across the tire’s tread width and at four places around the tire for a total of sixteen test points. In the course of the 30,000 mile test we measured tread depth of the new tires, and then eleven times throughout the test, most at 2,000-mile intervals.   

Some readers/subscribers have griped that nobody checks tires as often as we did and most certainly do not check alignments that often. To that end, we checked the tire’s inflation pressure just about every month, just like you should do. As for wheel alignment, we did check it routinely but never had to readjust the wheel alignment settings at all. And then there were our drivers, a sorted bunch of car enthusiasts, office administrators, and maintenance staff who drove the minivan all those miles. 

Minivans don’t excite many employees here with all the cars that we get to drive at our Auto Test Center, but with the enticement of free fuel, people were fighting over the use of the van, especially for long vacation trips. And so the van has been all over the New England region, and it enjoyed more places than I will ever see, from venturing into the deep-south of the United States to traveling across a wide swath of Canada.

At just over 30,000 miles, the tires still have about 25,000 miles or more left based on the fastest wearing groove, before they are worn-out to the tread wear indicator of 2/32” depth. On average, just two tires were about 50 percent worn out, one was just over 40 percent worn out, and a fourth tire had to be replaced after the previous tread measurement point due to an encounter with a large pot hole.  The tires were wearing faster at their shoulder grooves with a slight cupped shoulder. That continued to be the case at the last measurement, but the wear progressed more evenly across the width of the tire ensuring many more miles of happy travel. 

The bottom line: Our test doesn’t guarantee that you will get the same mileage. As they say, results may vary, as the total tire range depends on how and where you drive. But given the variability of our test with different drivers, roads, and seasons driven, we feel that with proper maintenance you can enjoy a long relationship with your Sienna’s run-flat tires.   

Background
Toyota Sienna all-wheel-drive owners clearly have a beef with the short tread life of the standard run-flat tires and continue to share complaints in letters and Cars forums posts, especially in Tire Talk, the online-subscriber-only tire forum at ConsumerReports.org. We've also covered the frustration of Sienna owners regarding fast-wearing tires here in the Cars blog.

As we’ve said before, most owners were pleased with the overall performance of their AWD Sienna—one of the top-rated models in Consumer Reports tests—but few are satisfied with the run-flat tire tread life, cost of replacement, and limited models from which to choose (two original-equipment suppliers). Some even have psychological fears about not having a spare tire on board.

Many owners have complained that the run-flat tires wear out much quicker than expected or unevenly—often within 15,000 to 20,000 miles. Some owners found themselves facing an aggravating annual tire replacement, costing $700 or more. Toyota finally addressed the issue last year with an extended warranty on 2004 to some 2006 model-year vehicles, mostly addressing the irregular wear condition. Later-model vehicles came with a revised tire intended to eliminate the wear condition.

—Gene Petersen, Jen Stockburger, Ryan Pszczolkowski

Related blog posts:
Update: Toyota Sienna AWD run-flat tires
Toyota Sienna AWD run-flat tires wear well for us
Toyota Sienna AWD tires - patience wearing thin
Toyota extends run-flat tire warranty
Toyota Sienna run-flat tires? Spare us.
Run-flat tires go flat with our readers       

Research tires with our expanded tools. Discuss in the Cars forums, especially in Tire Talk, the online-subscriber-only tire forum.

Snow test: Winter tire traction aids

Ever wish you had a little extra traction in the snow? We tested two products that promise to help you get up a slippery driveway.

Here's the scenario: You're driving home in snowy conditions. Maybe it's been snowing all day long, and the roads have been plowed well enough for you to make it to your destination—almost. Now all you need to do is ascend a steep driveway that is covered with unplowed snow. You make an attempt to climb the driveway, but the car tires are just spinning like mad. Now what? You could leave the car on the roadside and attempt to walk up to the house with your family in-tow, but that's not a great option. (I'm talking from experience here.) So, what if the solution was something you could grab from your trunk and apply to the tires in a few minutes, getting the family to the cozy comfort of home and the car tucked away, safe from passing snow plows? There are two products on the market that claim to deliver added tire grip to get out of a tight spot like this or worse: Tyre Grip and AutoSock.

Tyre Grip comes in a can and you spray it on the tire tread of each drive wheel.  Its claim is "better grip on snow, ice, and slush [by creating] an adhesive surface that grips the roads."  We bought a can for $24.95 plus shipping from an Internet store, though a 16-ounce can is now listed at $19.95 on the company Web site.

AutoSock is a cloth and mesh cover that you slip over the tire and wheel like a sock.  When installed, the AutoSock envelops the tire's tread and provides a gripping surface for traveling through snow. We purchased our AutoSock pair from TireRack for $99.00 plus shipping. They come in a variety of sizes to fit different tires. We bought ours to fit the 16-inch tires on our 2008 Honda Accord LX.

How they worked
We did some acceleration and brake testing in Vermont, comparing the grip of the all-season tires on our Accord with and without Tyre Grip applied. Our objective testing revealed a very modest 1-percent traction gain in accelerating with Tyre Grip and a more significant 5-percent gain in grip in stopping. Still, traction waned quickly after only traveling about 1 mile, far below the claimed 50 miles per application.

We didn't try the AutoSock in these tests, as wheel spinning, extreme braking and acceleration are not recommended. Further, AutoSock should only be used at speeds no higher than 30 mph.

The next test was our snow-covered hill climb test. We first tried to climb to the top of the hill, simulating our driveway scenario, with the Accord's all-season tires. We then applied the Tyre Grip to the tread and finished off using the AutoSock over the drive tires. The all-season tires failed to climb to the top of the snow-covered grade. Adding Tyre Grip did give a bit more starting traction, but not enough to reach the top of the hill. But with the AutoSock over the front drive tires, the Accord actually made it up the hill on numerous attempts. The winner here: AutoSock.

Bottom line
Tyre Grip might provide some added traction, but the cost per can is rather steep - you'll likely get only two or three liberal applications per can. Also, take note of the warning label: "Extremely Flammable, Harmful Vapor, and Harmful or Fatal if Swallowed."

The AutoSock is not cheap, but it can effectively get you out of a tight spot. The downside is that it's very cumbersome to slip over a tire—expect to get dirty and wet putting it on. The AutoSock is only meant for use on ice- and snow-covered roads and should be removed immediately when conditions improve. Also, the difference in grip it produces between axles with and without AutoSock will adversely affect handling. Finally, AutoSock warns that it's not a substitute for winter tires—we agree.

—Gene Petersen

See our winter tire buying advice and Ratings. And our complete guide to winter driving.

Redesigned tires section - tire ratings and sizes now easier to find

The Tires section at ConsumerReports.org has been redesigned, and we couldn't be more excited about the changes. Now, online subscribers can review the sizes each tested tire model is available in, making it easy to find the best tires for your vehicle. (These new charts eliminate the need to search manufacturer Web sites for available sizes.)

To get started from the Tires & Car Care page, or the Tires-specific landing page, you simply choose the type of tires you need.

We streamlined the tire categories as follows:

• Car Tires: regular all-season, performance all-season, and ultra-performance tires. 
• Truck Tires: all-season and all-terrain models. 
• Winter Tires: Q-speed rated tires (sometimes called "regular winter tires") and performance winter tires in higher speed ratings.

Pick a category and start your quest for the right tire to suit your needs. Unsure of what you need? We have helpful advice under How To Choose and Tire Size and Type accessible from any of the three tire categories, appearing as prominent links on the left side of the page. There's also direct links to CR Quick Picks, Ratings, and Ratings By Tire Size.  And you can get a more in-depth report by selecting Learn More About. 

As a reminder: CR Quick Picks are our top recommendations within a tire type. Ratings provides overall score and specific ratings of major performance categories like dry, wet, winter grip, comfort, rolling resistance, and tread-life (where applicable). Ratings by tire size gives the overall score for each model and the sizes in which each model is available, organized by wheel diameter. This feature also shows higher speed rated models  when available, which can be useful for those who might want to upgrade from, say, a S- or T-regular all-season tire to a performance or ultra-performance model with a higher speed rating.

The Tires home page still has useful links on general Buying Advice, Care & Safety, and CR blogs on tires.

We hope you enjoy the new redesign! Post your feedback below, and then join the Tires team in the Tire Talk forum.

—Gene Petersen, Jen Stockburger, Ryan Pszczolkowski

Take our new tire tread-wear test

In our November issue of Consumer Reports, we recommended using a quarter to determine when it’s good time to start shopping for new tires. (See “Tire Maintenance.”)

Since the story was published, some have mistakenly interpreted our recommendation as being that when tires have worn to 1/8” of tread depth that it’s time to replace tires. The measurement is about the distance between George Washington’s head on a quarter to the edge of the coin if you are using the quarter as a tread depth gauge. Let’s be clear: That’s a good time to start thinking about tire replacement, and begin researching and shopping.

At this depth, most tires still have some all-weather grip left, which gives you time to shop around for the best price and tire model that suits your car’s needs. Tires worn to the tread wear indicator bars (set at 1/16” and indicated by the use of a penny) in any or all of the grooves should be replaced immediately, leaving little time to shop for new tires.

In reality, consumers don’t often think about replacing tires based on tread depth alone.  Some wait until the steel belt edges show—that alarms us. We suggest changing tires earlier if your tires are losing grip in the wet or during winter driving conditions.   

If you’re in the market for car or truck tires, refer to our Ratings and all-new tire finder that can help identify the best tires for your ride. (Available to online subscribers.) 

—Gene Petersen

Update: Toyota Sienna AWD run-flat tires

The extended tread-life test on CR's Sienna AWD continues.

For those who have been following our saga of run-flat tires on our 2007 Toyota Sienna XLE AWD, we've been raking up the miles faster than you can say "minivans are the best family vehicle EVER!" After hearing many tales of premature wear of the original-equipment Dunlop SP Sport 4000 Self-Supporting Technology tires (DSST)—run-flat tires, in layman terms—we decided to do a long-term test to see for ourselves. After the traditional road test of our Sienna was completed, we purchased a new set of Dunlop SP Sport 4000 DSST tires for a tread-life evaluation. The evaluation started at the end of March, 2007, and is ongoing.

We've been checking inflation pressures religiously; aligning the wheels, rotating the tires, and measuring the average tread depth in no less than 16 test points around each tire at nearly every 2,000 miles. Admittedly, most consumers are not likely to follow our frequent alignment and rotation schedule, but we're giving the tires the best opportunity to wear optimally. So far, the results suggest that there are benefits in taking good care of your tires.

After some long vacations stints around Northeast parts of the United States and Canada, we've accumulated just over 22,000 miles. Our comprehensive tread-wear measurements tell us the tires still have plenty of life left. The tires are at least 32 percent worn out and some are closing in on the 40-percent mark based on the fastest wearing groove. Keep in mind that a tire is legally worn out when any one groove depth is flush to the tread wear indicator of 2/32 inch. Our Sienna's tires are showing more rapid tread loss at the shoulders, which is not uncommon for a radial tire, but we also observed a stepped wear condition to the inboard shoulder rib that started to appear around 19,000 miles. In addition, a cyclical tire whine is becoming very noticeable as the miles have accumulated.

We'll continue our put on the miles to see how the wear proceeds, including the step-wear condition.

—Gene Petersen

Related blog posts:
Toyota Sienna AWD run-flat tires wear well for us
Toyota Sienna AWD tires - patience wearing thin
Toyota extends run-flat tire warranty
Toyota Sienna run-flat tires? Spare us.
Run-flat tires go flat with our readers       

Discuss in the Cars forums, especially in Tire Talk, the online-subscriber-only tire forum.                                                                                                   

Winter driving safety

The winter season is upon us and that means—for those of us living in frosty locations—snow, ice, and cold. It can also mean hazardous road conditions and dangerous driving situations. Here are some tips on how to be prepared on the roads this winter. Also, check out our winter driving hub for advice on car maintenance, tires, and safety.

• Visibility is vital. In the winter months, visibility is compromised by the salt, dirt, and precipitation that are kicked up from other vehicles onto your windshield. Make sure you have enough windshield fluid and choose one that has antifreeze. If your wipers are showing streaks of water, it’s time to clean or possibly replace the blades.

• Check your charge. Before you go shopping for a new battery, get your battery tested by a repair shop as part of an annual safety inspection. It is particularly important to test your battery if it is more than two years old and you live in a warmer climate or four years old and you live in a colder climate.

• Inspect tires. It’s a good idea to replace worn tires before the winter months. Partially worn or fully worn tires can significantly reduce your ability to get going, turn and stop in snowy conditions. Consider replacing summer or all-season tires with a set of dedicated winter tires, which have tread patterns and rubber compounds specially designed to grip snow and ice.

• Check your cooling system. Extreme cold can cause rubber parts to become brittle and fail. Check the radiator and heater hoses for cracking, leaking, or contamination from oil or grease. The hoses should be firm yet pliable when you squeeze them. Replace them if they feel brittle or overly soft. For most vehicles, the cooling system should be flushed at least every two years (check your owner's manual). This helps keep corrosion from building up in the system. The system should be refilled with a mixture of antifreeze and water, typically in a 50/50 ratio. This will keep your coolant from freezing to well below zero.

• Fill ‘er up. Make sure you have half a tank of gas in your car during the winter months as it will help prevent it from freezing in very cold temperatures.

ADDITIONAL ITEMS FOR WINTER DRIVING

For the cold, wet conditions of winter, you may need additional items in an emergency kit, especially if you travel in remote areas or in severe conditions.

Windshield scraper. Good visibility is your most important safety item, but persistent snow and ice can build up quickly and make it hard to see. A long-handled, soft-bristled brush can also come in handy.

Tire chains and tow strap. Familiarize yourself with how to put the chains on your vehicle's tires or attach a tow strap before you need to do it in cold and possibly dark conditions.

Blanket and winter hat. If you run out of fuel or if your battery dies, the vehicle won't be able to provide heat. A blanket and hat can help keep you warm if you have to wait for a long time in cold conditions.

Chemical hand warmers. These small, inexpensive packets are available at ski shops and sporting-goods stores.

Small folding shovel. If you get stuck in snow, this can be a vital tool. A folding camping-style shovel will require more digging effort than a longer-handled shovel, but is more convenient to store in the vehicle.

Bag of cat litter. This can help provide some traction on an especially slick road surface.

—Liza Barth

Run-flat tires do have their advantages (and fans)

We received many responses to our story on the pros and cons of run-flat tires.

People often indicated that we'd missed the mark and that, in their opinion, the safety benefits of run-flat tires certainly did not outweigh the problems. Our reader/subscriber letters agreed that run-flats have issues:

• Difficult to find replacements in certain areas
• Limited number of replacement models
• Inability to repair run-flats
• High replacement costs

Some even said that these issues were greater concerns than most were willing to live with -- even with extended the mobility run-flats offer. However, after suffering a flat this past Thanksgiving eve, I'm still convinced that run-flats do, indeed, offer a safety benefit.

Let me explain.

Much of the pre-Thanksgiving traffic was in full swing, as many businesses closed on time (if not early) to allow their employees to get home early. I'd signed out our Sienna AWD minivan (equipped with run-flat tires) for the long holiday weekend to travel to Vermont with my family and to add miles to the tires for our ongoing long-term wear evaluation. I picked up my children from daycare—two kids ages three and eight—and put them in their child seats. The van was also full of all the stuff I needed for the weekend: cocktail party supplies; a movie screen for entertaining the children during the party; folding chairs that I borrowed for additional seating on Thanksgiving and for the party; and a mix of food and beverages... You get the picture.

As we're traveling on a rural—and particularly narrow—Connecticut road, we came up over a knoll to find an approaching pickup towing a trailer and taking a bit more than its fair share of the road. I'm somewhat forced to go a bit farther to the shoulder than I normally drive and end up hitting something (I'm not sure if it was simply a pothole or a rock) rather hard. I hadn't gone fifty yards when the Sienna's tire-pressure monitoring system lights up—I knew I had a flat.

Well, let me just tell you if I had been driving on standard, non-run-flat tires and needed to make a tire change, I'm fairly sure that I would not have been able to do it safely in the location I was in without putting my children, myself, and the Sienna in serious danger. You see, the same knoll that prevented the approaching pickup from seeing me would have prevented anyone from seeing my tire-flattened Sienna as well. Thinking back, I'm fairly sure I would have sacrificed the wheel and would have simply driven on the flat tire until I could have gotten out of that location.

But...as luck would have it, I quickly and almost joyously remembered: THE SIENNA HAS RUN-FLATS! Not only would I be able to safely drive myself and my family home (albeit a bit slower), I wouldn't be standing in the middle of the road unloading my children, food, drinks, movie screen, and chairs in order to change a tire.

A day later I drove—carefully, mind you—on that same tire without any pressure in it to a location where I could get the flat changed.

Admittedly, before this all happened, I could have only envisioned a variety of scenarios where run-flats would have been beneficial in the event of a flat -- a busy highway, an uneven shoulder where jacking a car could be dangerous, or in very poor or cold weather. Little did I realize they'd be my saving grace on such a dark Thanksgiving eve with kids and a load of stuff on a narrow country road in Connecticut.

—Jennifer Stockburger

Share your experiences in the Comments below, or in our Cars forums.

Related blog posts:
Update: Toyota Sienna AWD run-flat tires
Toyota Sienna AWD run-flat tires wear well for us
Toyota Sienna AWD tires - patience wearing thin
Toyota extends run-flat tire warranty
Toyota Sienna run-flat tires? Spare us.
Run-flat tires go flat with our readers   

Michelin champions tire rolling resistance

Tires have a large impact on vehicles' fuel economy. At an event in New York City last week, executives at Michelin tire said that after discounting engine and other losses, tire rolling resistance accounts for about 20 percent of the energy needed to power a car. Overall, Michelin figures that tires account for about 3 to 5 percent of the nation's CO2 emissions and about 9 percent of U.S. oil consumption.

In a country burning nearly 4 billion barrels of gasoline and diesel fuel per year for transportation, as the United States is, that's a lot of fuel going to turning tires. Doing the basic math, 3 percent of 4 billion barrels is about 120 million barrels a year. Rolling resistance varies with tire wear, condition, alignment, load, speed, inflation pressure, and road texture, so exact calculations are difficult to come by.

Jim Micali, president of Michelin North America, says that the company's next-generation Energy Saver tire can cut rolling resistance by a further 20 percent over its current line of low-rolling-resistance tires. Michelin expects that a 50-percent reduction in resistance is possible in the next 10 to 15 years. A 20-percent reduction in rolling resistance would be equivalent to a 3-percent savings in fuel consumption for drivers.

At the same time, the company turned on a Times Square billboard (in conjunction with similar ones in Berlin, Paris, and Shanghai) to track how many gallons of fuel the company says drivers have saved worldwide by using its current Energy series of high-mileage tires, compared with the industry average for rolling resistance. The number started out at 2,380,056,909 gallons, and it is increasing by 11.6 gallons per second. (See the latest numbers in the online green meter.)

In our recent new-car testing, we have seen that cars and trucks with low-rolling-resistance original equipment tires sometimes sacrifice grip. Some tire suppliers say some auto manufacturers put higher priority on low-rolling resistance over other performance criteria. In testing aftermarket all-weather tires, we have found that it's possible to get a very good performing tire with low-rolling resistance compared to other tire replacement tires. And Michelin says its upcoming line of low-rolling-resistance tires will save energy without shortening tread life or reducing grip.

The state of California is working on developing a rating for tire rolling resistance, which it plans to require tiremakers to print on the tire sidewalls starting in 2009. Meanwhile, to help consumers choose the appropriate replacement tires, the California Energy Commission is developing a complete database of all replacement tires marketed in the state. The database should be available in 2007 or 2008. Today, tires are required to have ratings printed on the sidewall for traction, tread life, and temperature.

Consumer Reports supports increasing consumer awareness of tire efficiency, which is why we test and provide rolling resistance ratings in our tire performance studies. Rolling resistance is one of many key performance attributes Consumer Reports tests as part of its tire ratings.

Giant billboards like the one in Times Square may help raise awareness of the problem to a small degree, although it omits savings by any other tiremakers' products. In the effort to be perceived as a "green" company, it is hard to miss the irony of using megawatts of electricity to deliver the message. Still, if the savings are that big for one brand, there are clearly more gallons to be saved across all brands that offer low-rolling resistance tires. CR recommends that consumers consider a lower rolling resistance tire as a tie-breaker between two or more models, but don't sacrifice the safety of good grip for low rolling resistance.   

--Eric Evarts

updated 7/16

SEMA - Tesla and Yoko become green partners

The Tesla is coming, finally. After numerous delays, we were told by a Tesla representative that all systems are go for a Spring 2008 launch for the much-hyped electric supercar. The battery-powered Tesla, which is said to achieve a 0-60 mph time of near 4 seconds and reach of speeds of 135 mph, was at the Yokohama Tires stand at the SEMA convention in Las Vegas. Yokohama is an original-equipment supplier for the Tesla, shoeing the roadster with its ultra-high performance Advan Neova LTS tires.

Yokohama used the near-guilt-free sports car to play up their all-new passenger tire, the Super E-Spec, a tire that combines citrus oil with rubber to form a new compound that Yokohama calls "Super Nano Power Rubber." Yokohama says that the tire greatly reduces the use of petroleum products in tires, thus helping save natural resources.

—Cliff Weathers

Discuss SEMA in our Auto Show and Aftermarket forums.

Nitrogen in tires - Q&A

Our recent blog post, "Tires - Nitrogen Air Loss Study", looked at using nitrogen in tires. So far, it has generated a lot of interest. In fact, that post has received more comments than almost any other. Among the comments were many questions--more than could be addressed in a simple comments format.

Senior tire engineer and program leader Gene Petersen has compiled answers to the comments thus far, adding further insights into the testing and the results. A tires Q&A is presented below.

For further discussion, online subscribers are invited to engage the experts and other consumers in the "Tire Talk" forum.

For quick background on the nitrogen test:
Consumer Reports wanted to find out if nitrogen is worth the price for passenger vehicles, so we evaluated pairs of 31 tire models of H- and V-speed rated, all-season tires used in our tread wear test from 2006. We filled one tire per model with air and the other with nitrogen. The test was quite simple: fill and set the inflation pressure at room temperature to 30 psi (pounds per square inch); set the tire outdoors for one year; and then recheck the inflation pressure at room temperature after a one year period.

Read the original post.

Q: Were the tires installed on a vehicle? Would the weight of a vehicle have a greater effect on the loss of psi?
A: The tires were initially inflated indoors at room temperature and then stored outdoors for one year on a specially built tire stand to keep them separated. After one year the tires were returned to the indoor location and inflation was checked at room temperature. Our test was a controlled comparison with many tire models. Plus,  we did not install them on vehicles, which may or may not have been another variable.

Q: Seems to me that since the difference is so small and nitrogen is difficult to get and more costly that it is not worth the effort and the cost.
A: That's  a logical conclusion.

Q: Were the tires on new rims or older ones?
A: The tires were taken from a tread wear test we performed last year. The tires had 16,000 miles of simulated travel on the wheels, so technically the tires and wheels are used products. But I want to mention that the tread wear test ensured that the tires were well seated to the wheels.

Q: I have nitrogen in the tires on my Prius and noticed an immediate improvement in gas mileage of 3-5 mpg. Better gas mileage was the selling point when the dealer suggested the change. I'm interested to know why gas mileage was not part of the test.
A: Fuel economy is related to the tire's rolling resistance, which is a function of load and inflation pressure. High load or low pressure causes a tire to have higher rolling resistance and, therefore, lower fuel economy. If the nitrogen retains the pressure better than air in a tire, fuel economy might benefit. But I cannot think of another reason why fuel economy would solely improve based on using nitrogen in lieu of air. Overall, if you can maintain proper inflation pressure, then fuel economy will be optimum.

Q: I just thought I'd remind everyone that nitrogen makes up like 75-78% of ambient air, so air verse nitrogen should make little or no difference.
A: Yes, nitrogen makes up most of the air -- about 78% as you point out. Think about this, though: if you fill your tires with air, the oxygen is more likely to permeate out of the tires before the nitrogen and over time you end up with a higher concentration of nitrogen. I have not checked this but it seems possible.
An additional point: not all air is of equal quality. Moisture, oil from the air compressor, and other pollutants can affect tire integrity.

Q: I just had nitrogen added in our 1999 [Saab] 9-3. I'm getting roughly one mpg better than before.
A: Interesting. Maybe the tires were under-inflated before you had the nitrogen fill.

Q: The test implies the tires simply sat outside for a year and were not driven or used during that time. What good is that? Tires get used. Without testing the impact of actual wear and tear, this test is useless. Why not fill a long-term test vehicle with two nitrogen tires and two air tires and then drive it for 10k miles and inspect for wear, psi, etc?
A: The intent of the study was simply to answer how well air and nitrogen are retained in a tire. This methodology allowed us to chart the differences across more than 30 tire models in controlled conditions -- a laboratory process we would not have been able to replicate driving the vehicles. We did not explore the claimed benefits of nitrogen on limiting tire aging or look at the dynamic effect of gas permeation under operation. Those interesting topics were beyond the scope of this test. Also, wear effects would largely be affected by maintaining proper inflation pressure regardless of the gas used (air vs. nitrogen).

Q: I think we are missing some of the advantages here. First, the air loss mentioned above is 2.2 vs. 3.5 psi. That is a significant difference, even at this low inflation pressure. Also, nitrogen is an inert gas, and so will react with the rubber/chemical compounds much less, contributing to reduced wear. Another point is that nitrogen will not heat up like oxygen, so during extended highway driving you will reduce the over-inflation and wear/tear resulting from heat build-up.
A: Interesting points. Because nitrogen, in our case, is a processed gas (moisture and oil was filtered out by our nitrogen generator), you might expect better inflation control as the tire heats up under normal service vs. air with unregulated moisture, etc. And nitrogen has been shown by the government and industry to reduce tire aging.

Q: This seems like a flawed test because the tires weren't tested under "normal operating conditions."
A: Tires are designed to perform as intended with air, and the tire manufacturers tell us as much. Assuming that proper inflation pressure is maintained,  the tires will run as designed using air or nitrogen.

Q: What about daily, weekly, and/or monthly fluctuations due to significant changes in the ambient air temperatures? Would you expect that the psi variation due to ambient air temperature changes over shorter periods of time could be much more pronounced?
A: We did look at the inflation pressure over various ambient temperatures but could not find a significant difference between air and nitrogen. We are not making any claims here, but just telling you what we found. 

Q: A flawed study and analysis. And sadly quiet on the advantages of using nitrogen in heavy trucks where 18 tires need to be maintained weekly to pressures of 100 psi.
A: The positive benefits of nitrogen in high(er) service pressure applications, such as used in large truck tires, has been documented in the industry. Our test centered on passenger tires, only. We are not discrediting the use of nitrogen, but it is not a substitute for regular inflation checks.

Q: I think the bottom-line comment about being sure to check pressure regardless of air or nitrogen is key. I think the tendency would be to NOT check nitro filled tires as frequently as air filled.
A: I agree. People might think that once nitrogen is used to inflate tires that they no longer need to check the inflation pressure. Hopefully these tire blogs and discussion with our faithful readers will be a good reminder that there's no substitute for regularly checking your car's tires.

Learn more about tires and see the results from our latest tests in the Tires section of ConsumerReports.org.

Tires - Nitrogen air loss study

Filling tires with nitrogen rather than air is becoming a common practice in the replacement tire market. This service offers tire dealers another avenue for making money while also promoting safety. The claimed safety benefits often include the potential for reducing air loss compared to an air-filled tire. Maintaining proper inflation can help prevent tire overheating; promote optimum tread life; and reduce rubber aging and wheel corrosion. The use of nitrogen in large truck fleets and the commercial tire industry are well documented and support these claims.

The National Highway Traffic Safety Administration (NHTSA) has seen reduced aging of tires filled with nitrogen. Though the data does support that passenger car tires could benefit by all the claims made for nitrogen, tire manufacturers say that they already design tires to perform well with air inflation. And while nitrogen will do no harm, manufacturers say that they don't see the need to use nitrogen, which generally adds $5 or more per tire charge.

Consumer Reports wanted to find out if nitrogen is worth the price, so we purchased a Nitrogen Inflation System and checked out how well the inflation held up over a one year period. We evaluated pairs of 31 tire models of H- and V-speed rated, all-season tires used in our tread wear test from 2006. We filled one tire per model with air and the other with nitrogen. The test was quite simple: fill and set the inflation pressure at room temperature to 30 psi (pounds per square inch); set the tire outdoors for one year; and then recheck the inflation pressure at room temperature after a one year period.

The tires were filled and deflated three times with nitrogen to purge the air out of the tire cavity. We also used an oxygen analyzer to be sure we had 95-percent nitrogen purity in the tire--the claimed purity limit of our nitrogen system, which generates nitrogen gas from ambient air.

The test started on September 20, 2006 and the final measurements were taken on September 20, 2007.  The results show nitrogen does reduce pressure loss over time, but the reduction is only a 1.3 psi difference from air-filled tires. The average loss of air-filled tires was just 3.5 psi from the initial 30 pressure setting. Nitrogen-filled tires lost an average of 2.2 psi from the initial 30 psi setting. More important, all tires lost air pressure regardless of the inflation medium, so consumers should check their tires' air pressure routinely. No evaluation was done to assess the aging claim.

Bottom line: Overall, consumers can use nitrogen and might enjoy the slight improvement in air retention provided, but it's not a substitute for regular inflation checks.

--Gene Petersen

Added 10/11/07:

There has been great interest in this topic, as evidenced by the comments. Among the user posts are many questions—more than could be addressed in a simple comments format. We have posted a "Nitrogen in Tires Q&A" directly answering many of these questions.

Read the latest tire Ratings and advice. Discuss Tires in the Consumer Reports forums.

New presidential candidate for tire-wear testing

George Washington is legendary for many reasons, but he may be adding a new posthumous distinction as a tire tool, based on recent tests.

Traditionally, tire-wear advice has been to measure the tread depth using a penny, with Abe Lincoln’s copper head at 2/32-inch being the universal signal to replace a car’s rubber. However, Consumer Reports general advice has been for people routinely driving in heavy rain or winter conditions to consider replacing the tires closer to the 5/32-inch groove depth, which marks the half-tread point on many tires.

Recent testing by retail giant The Tire Rack confirms our long-standing guidance, and their recent PR campaign is getting this important advice to consumers. As they put it, using Washington’s head on a quarter (which represents 4/32-inch tread depth) may be a better gauge of when a tire’s traction has diminished significantly. We agree.

Using a 2006 BMW 325i and 2006 Ford F-150 Super Cab 4x2, The Tire Rack tested original fitment tires in new, 4/32-inch, and 2/32-inch conditions. The wet braking results show a dramatic difference that should be a real wake-up call for motorists. (Read the full report.)

While most states consider 2/32-inch to be the legal limit, lead by the federally mandated tread-wear indicators, we recommend replacing tires sooner for those typically driving through poor weather. Right now, our tire engineers are validating data from an extensive tire-wear performance test to be posted online in the weeks ahead. In addition, the latest ultra-high performance tire tests to be published, and posted, in a couple months will report on the most extensive tread-wear testing performed by a North American consumer publication. From the combined results, we’ll provide advice not only on when to buy, but also how to select a tire that will give the best performance and most miles for your application.

To learn more about tread-wear safety, read our updated report “How safe are worn tires?"

--Jeff Bartlett

Toyota Sienna AWD run-flat tires wear well for us

The extended tread life test on CR’s Sienna AWD continues. And so far, so good. But let’s recap…

Toyota Sienna all-wheel-drive owners clearly have a beef with the short tread life of the standard run-flat tires and continue to share complaints in letters and Cars forums posts, especially in Tire Talk, the online-subscriber-only tire forum at ConsumerReports.org. We've also covered the frustration of Sienna owners regarding fast-wearing tires here in the Cars blog: "Toyota extends run-flat tire warranty" and "Toyota Sienna run-flat tires? Spare us."

As we’ve said before, most owners were pleased with the overall performance of their AWD Sienna--one of the top-rated models in Consumer Reports tests--but few are satisfied with the run-flat tire tread life, cost of replacement, and limited models from which to choose (two OE suppliers). Some even have psychological fears about not having a spare tire on board. To recap, many owners have complained that the run-flat tires wear out much quicker than expected or unevenly--often within 15,000 to 20,000 miles. Some owners found themselves facing an aggravating annual tire replacement, costing $700 or more. Toyota finally addressed the issue last year with an extended warranty on 2004 to some 2006 model-year vehicles, mostly addressing the irregular wear condition. Later-model vehicles came with a revised tire intended to eliminate the wear condition.

Our AWD Sienna
We purchased a new 2007 Toyota Sienna XLE AWD (ratings available to online subscribers) with the Dunlop SP Sport 4000 Self-Supporting Technology tires (DSST). After the road test was completed, we purchased a new set of Dunlop SP Sport 4000 DSST tires for a tread life evaluation on the Sienna AWD. The evaluation started at the end of March and at this point in July, we have a little more than 11,200 miles on the tires. We’ve been checking inflation pressures religiously, aligning the wheels, rotating the tires, and measuring the average tread depth in no less than16 test points around each tire every 2,000 miles. Now, most consumers are not likely to follow our frequent alignment and rotation schedule, but we’re giving the tires the best opportunity to wear optimally. 

So what have we found up to now? In short, not much yet--the tires are less than 20 percent worn-out to the tread wear indicators, the wear is relatively even across the tread width, and we’re not observing any abnormal wear condition.  At this early stage, the tires appear to be able to last more than 45,000 miles, even exceeding Toyota’s estimate of 40,000 miles noted in their Tire Information booklet. Still, we recognize that to get a more accurate picture of projected tread life, we’ll need more miles. We plan on doing just that with the hopes of reaching 20,000 or more miles by the end of summer. That shouldn’t be a problem, with many of our colleagues taking the minivan on extensive summer trips.

 

NOTE: An updated has been posted: "Update: Toyota Sienna AWD run-flat tires"

--Gene Petersen

Related blog posts:
Update: Toyota Sienna AWD run-flat tires
Toyota Sienna AWD run-flat tires wear well for us
Toyota Sienna AWD tires - patience wearing thin
Toyota extends run-flat tire warranty
Toyota Sienna run-flat tires? Spare us.
Run-flat tires go flat with our readers  

Tire testing by the numbers

Gene Petersen, Jen Stockburger, and Ryan Pszczolkowski could probably land spots on a pit crew if they ever chose to leave Consumer Reports. The three of them do the bulk of our tire testing at our Auto Testing Division, which means, among other things, performing some 2,600 tire changes last year alone. That’s enough to routinely wear out the studs that hold lug nuts to the hubs--despite  liberal doses of silicone and careful torque wrench use. Few cars will ever see anywhere near 2,600 tire changes between the assembly line and the scrap heap. But then again, most magazines don’t buy several hundred tires for testing every year.

Regular readers know that Consumer Reports conducts the most thorough car testing program of any magazine or Web site in the United States, but even CR junkies may not realize how extensive our tire-testing program is.

For the last report, we bought 572 tires, including duplicate sets and spares. To minimize damage to the tires from changing, we also bought 150 identical wheels. The goal is to have all the tires in-house by November, to give us a couple of months to catalog and mount them. By January, we’re ready to begin.

One car was bought new specifically for the tire testing program this year, an Audi A3 for performance-tire testing. Last year it was a Honda Accord for all- season tires. Each car quickly ran up close to 14,000 miles, mostly at our track.

These are some hard miles. Days of hard braking, handling tests, flat-out acceleration and circling the skid pad in all kinds of weather take their toll on the cars, as well as the tires. The cars routinely wear through at least one set of brake pads before the six months of testing are through, and they’ve also worn out brake master cylinders, suspension parts, and at least one transmission. 

When all is said and done, the tire test car will have made more than:

·        430 trips through our avoidance maneuver course. (Note to Gene, Jen, and Ryan: Light breakfast.) 

·        860 laps around the skid pad. (Skip lunch.)

·        1450 stops from speed in the dry, wet, and even on ice. (Maybe just start fasting altogether.)

But the really big number comes from our wear testing, which helps determine how long you can expect the tires to last on your car. In 2006, we racked up a grand total of 1,120,000 miles.

At least the wear testing can be done on a full stomach.

--Jim Travers

Tire maintenance tips

Federal officials have ordered the recall of 450,000 tires imported from China.  These lack a safety feature that prevents the tire tread from separating. While Consumer Reports has not tested this brand of tires, it's important to follow the basics of proactive maintenance and inspection, particularly with summer just starting. Heat is the enemy of any tire, and with summer heat combined with high levels of summer travel, we recommend that consumers do the following:

• Inspect your tires. Replace any worn out tire as well as any tire with a bulge, crack, or cut. We'd even suggest replacing all four if they're nearly worn out. This keeps the best tread on all four corners of your car instead of only one. Check the wear across the tire's tread and determine if it is wearing evenly or wearing more on one side than the other. Uneven wear could be a telltale sign of wheel misalignment, suspension damage, or wrong inflation pressure. Have the vehicle serviced.
• Check the inflation pressure. It is important to do this routinely, preferably monthly. The correct inflation pressure is on a tire information placard found on the driver's door jamb. Adjust the inflation pressure when the tires are cold or when the car has been parked for three or more hours. 
• Watch the load capacity. Adhere to the vehicle load capacity recommended on the tire information placard. Too high a load and/or low pressure will overstress a tire and could lead to failure.
• Check your steering. Should you experience a vibration or steering pull, stop and inspect the tires, and replace a tire with the spare if needed. If you can not determined a tire abnormality, then either drive or have the car towed to a service center immediately. Always avoid highway speed travel on the way to the service center.

When it comes to your tires, consult our performance ratings on the tire that best suits your needs. Also, see our complete Ratings and recommendations on all of the tires that we've tested. For more in-depth information see our reports on the early signs of tire failure and tire maintenance. 

--Jon Linkov

Run-flat tires go flat with our readers

Consumer Reports explored the pros and cons of run-flat tires in a June 2007 story called "Run-flat tires safety benefits outweigh problems." The article outlined some of the disadvantages and basic inconveniences of run-flat tires. Not surprisingly, this story elicited a wave of mail from our readers/subscribers who weren't shy in adding their two-cents. Much of the responses reinforced the limitations we noted in the article, including premature wear, stiff ride, high replacement costs, and limited replacement choices. We read every e-mail and letter and tried to sum up the complaints below.

Keep in mind that we're talking about only a few correspondences, so there is no scientific data from which to make conclusions. Nevertheless, here are a few common themes:

• A punctured run-flat tire may provide extended mobility, but with routine run-flat tire ranges of just 50 to 100 miles, it's far more limiting than having a conventional spare tire. One person had to spend an extra night at a town in New Mexico to get a tire from a local dealer the next morning. Another letter was more direct: "...50 miles is completely worthless..." (referring to run-flat tire capability). "I would not put my wife and kids on run-flats."
• Limited availability and accessibility were common concerns, but the high cost of replacement of a run-flat was a common comment. Additionally, a few letters noted that not only did people have to replace the flat run-flat tire, but that the wheel was damaged and had to be replaced, too. 
• Underwhelming tread wear life was noted by a few, with a few harsh words about tires lasting just 18,000 to 20,000 miles. Plus, the high replacement cost rankled many.
• Interestingly, some run-flat tire makers do not recommend repairing a run- flat tire given its uncertain condition after running flat even for a short period of time. This rubbed a few readers raw, and some noted that standard conventional tire punctures can often be repaired. 
• One reader noted that he was not informed of the limitation of run-flat tires by his new-car salesperson. He claims to have only been told about this after he had a tire problem with the new vehicle. Apparently, the dealership discourages buyers from purchasing that model car with the run-flat package. But the horse was already out of the barn.

Undoubtedly the letters will continue, and we look forward to reading them and post in our Tire Talk forum (available to ConsumerReports.org subscribers). Few readers/subscribers ever write to us about the positive aspects of a product, but we'd be interested in hearing from those folks, as well. Run-flat tire technology may be sound, but readers are clearly saying there is much room for improvement. Will run-flat tires succeed in the market place, or go the way of Oldsmobile, Plymouth, and DeLorean? So far, the jury's out.

--Gene Petersen

Related blog posts:
Update: Toyota Sienna AWD run-flat tires
Toyota Sienna AWD run-flat tires wear well for us
Toyota Sienna AWD tires - patience wearing thin
Toyota extends run-flat tire warranty
Toyota Sienna run-flat tires? Spare us.
Run-flat tires go flat with our readers

Illuminating test - Light-up tire pressure monitors

Want to maximize your gas mileage, reduce tire wear, and improve safety? Well those are the sort of claims made by the makers of the Air Alert Valve Cap System. The caps they’re selling are the simple screw-on type with valve indicators that blink once the tire’s air pressure falls about 4 pounds per square inch (psi) or more from the initial cold inflation pressure of a tire. We bought a set of four for $24.95 direct from Aviation Upgrade Technologies to try them out for this blog-exclusive look at tire pressure monitoring systems.

Valve cap sensors aren’t new; we tested a mechanical color-coded sensor some years ago under the Accu Pressure name. They worked OK, but we had problems trying to read the color-coded display, which dimmed over time due to moisture fogging. They also required stooping down close to the sensor to read the display. Plus, the sensor was susceptible to road curb damage, and we even had a set stolen on a parked car during our test.

We found that these new, blinking Air Alert stems more accurately sensed pressure changes. Think digital pressure gauge to mechanical stick pressure gauge in comparing it to previous mechanical systems.

The instructions are straightforward and the caps are simple to install, but it’s necessary to follow the instructions precisely to initially calibrate the caps to your car tires’ recommended inflation pressure. 

• Set your tire’s pressure to the recommended inflation pressure and then install the cap. It screws on like a regular valve cap.
• The cap will automatically measure and retain the pressure setting for the life of the cap.
• Should the pressure drop 4 psi or more from the initial pressure, the top of the cap will blink red until the pressure is restored.

We bench-tested each of the four valve caps and found them to accurately flash when the pressure dropped 4 psi +/- 1 psi as claimed by the manufacturer.  In fact, against our pressure calibration gauge, the caps worked within about one half of a psi (+/- 0.5 psi), notably better than claimed. (Aviation Upgrade Chief Executive Officer Torbjorn Lundqvist says that caps are checked at the factory to be within specification of +/- 0.5 psi, despite the advertised claimed tolerance of +/- 1 psi.) We then installed the caps on a Chevrolet Silverado pickup and compared them to the truck’s own tire pressure monitor system, which displays individual tire pressures. Each time the tire pressure fell 4 psi or more, the Air Alert flashed.

Pros:

• The caps are relatively small, just about 1” x ½” in size, so they should be fairly discreet, and they only weigh about 0.35 oz. each.
• We didn’t experience any tire imbalance, but it’s probably a good idea to have the tires rebalanced to compensate for the weight of the valve cap. Mr. Lundqvist says a more miniaturized version of the cap is in the works.
• Accuracy may be satisfactory, but durability is still an open question. They do have a long-life battery -- good for about two years of service or just three weeks if a flashing light condition persists.
• The caps are suitable for a wide range of cars, trucks, trailers with tire pressures from 10 to 110 psi.

Cons:

• Mess-up the initial calibration of the valve cap and you end up with a non-functional system.
• Like all valve cap sensors, you have to walk around the car to observe each tire. We found the blinking light noticeable in most light conditions and it was far easier to detect than some mechanical color-coded pressure loss systems. But we agree with the manufacturer’s advice: the system is not meant as a substitute for monthly tire pressure checks.
• Four psi is a narrow window of air loss particularly with a tire that operates at high air pressure. The natural variance of pressure resulting from the changes in air temperature might routinely trigger the caps to flash. As a comparison, the government-mandated tire pressure monitoring system (which will be mandatory on all new cars starting in 2008 model year) requires activation at margin of 25 percent loss from the vehicle’s recommended air pressure setting. For a vehicle like the Chevrolet Silverado, that would be about 8.8 psi less, resulting in fewer false alarms than the Air Alert System. But, of course, the Air Alert System is providing a more stringent and better early warning system.
• Like all twist-on pressure cap systems, it’s critical to properly hand-tighten the cap. Leave the cap a bit loose and it could actually bleed air out of the tire. And because the caps do stick out a bit more than regular valve caps, they get damaged from curbs.
• Finally, some states restrict use of blinking lights on the wheels; some devices are clearly cosmetic with brilliant illumination. It’s not clear if these add-ons are affected by the same restrictions since the light is not normally on when the tire is properly inflated and the illumination is subdued. But it’s probably a good idea to contact your state department of motor vehicles for advice first.   
• The batteries are not replaceable.

If your car doesn’t have tire-pressure monitors and you’re looking for an economical and simple way of ensuring that your tires are not under-inflated, consider the Air Alert System.

--Gene Petersen

What tires are on your car?

Do you know what kind of tires are on your new car? Most consumers don't, even though tires are a critical safety and performance item. All that connects a vehicle to the road are four palm-sized contact patches. Put that way, it's clear that the right tires can make all the difference.

We've found that your new, or nearly new, ride is likely to be shod with performance tires carrying a speed rating of H or higher (above 130 mph), based on a review of how the 2006 CR-tested cars and trucks were equipped. Granted, our snapshot-view of the market may not represent the actual mix of passenger vehicles sold every year, but the 67 models we tested that model year do cover a wide range of vehicles, from small economy cars to ultra-performance sports cars. And, of course, it includes a fair mix of family sedans and SUVs. The good news is that these performance tires deliver crisp handling and better cornering grip at sane speeds. The bad news is that they may wear out at a faster rate than regular all-season tires.

Size matters
Just as the vehicle market proliferates and diversifies, the number of available tire sizes seems to grow. Among the 2006 models surveyed, there were 41 tire sizes; some even require different front and rear tires (called a staggered fitment). Wheel sizes ranged from a small 14 inches for the Hyundai Accent and Kia Rio to a massive 19-inch wheel diameter for sports cars like the Dodge Viper. On wheel size alone, the most common diameter (17 inches) was found on 43 percent of the vehicles, followed by 16-inch wheels at 27 percent. Once common, 14- and 15-inch wheels only accounted for 9 percent of the mix, while once rare 18- and 19-inch wheels account for 21 percent of the 2006 models surveyed.

Go, Speed Racer
Most tires have a speed-rating symbol on the sidewall to indicate the maximum safest speed the tire can be driven. The speed capabilities of most tires are well above legal limits, but higher speed-rated tires generally possess greater levels of handling and cornering grip. Conversely, higher-speed-rated tires generally don't have the all-weather grip or tread wear life of lower-speed-rated tires. S is typically the lowest speed rating found--still good for 112 mph and representing the bulk of the replacement tires on older model cars and trucks. But S-rated tires are a rarity among new vehicles, with only seven percent of 2006 cars and SUVs surveyed being so equipped. Another 12 percent of these vehicles came with slightly higher-speed-rated tires of T, good for 118 mph. We also found that 35 percent of the vehicles came with performance rubber, such as H speed-rated tires (130 mph) and 27 percent came with V-rated tires (149 mph). Ultra-performance tires with an even higher speed rating of Z (above 149 mph, and include W- and Y-rated models) accounted for a significant 18 percent of the 2006 models.

We also found that the speed rating of tires can change with the trim-line of the vehicle. For example, the Honda Civic Hybrid takes an S-rated tire; the Civic EX has an H-rated tire; and the Civic Si comes with a V-rated versions. Maybe an even more extreme example is with the Chevrolet Monte Carlo, where the base LS has an S-rated tire in the P225/60R16 size, but the SS model (tested by CR) came with an ultra-performance P235/50R18 W-rated tires. Replacing the 16-inch tires on the LS will cost about $69 per tire, but replacing the tires on the SS will set you back about $233 per tire--and that's replacing original equipment tire with the same models. The good news is that there's a wide variety of replacement tire models available for many size tires that come on new vehicles. As an example, the 205/55R16 size tire, which came on 15 percent of our 2006 vehicles, was priced from about $60 to $160 depending on tire make, model, and type.

So, you still need to ask yourself: Do you know what's on your car? Or the one you are considering purchasing? Check the information placard found on the car's door jamb.
For more tire information, read "Choosing size & type" and check out the performance ratings for tires that fit your car.

-- Gene Petersen

TireTalk Forum: Where the rubber meets the road

Since we never get tired of talking about tires, we thought we'd help you find everything you always wanted to know about tires and CR's tire coverage. This is designed to be enTIREly comprehensive.

How to find the TireTalk forum
(available to ConsumerReports.org subscribers only)

• From the CR's Cars main page, click on the Forums link. TireTalk is one of the top green links; the color indicates that this is a premium forum for subscribers only.
• From anywhere in the Cars section of ConsumerReports.org, you can also go to the Tires section by using the dark blue horizontal navigation bar. TireTalk can be found underneath the three featured tests on the top left side.
• Better yet, bookmark our main Cars forum pages so you'll always be one click away from talking cars with our staff experts and fellow readers.

Now let's talk tires
This forum has over 5,500 discussions on tires, where you can ask advice or share an experience if you are an online subscriber, or read various discussions if you are non-subscriber. It's a fascinating site covering questions on practically anything related to tires. You can get some direct advice from the CR tire test engineers, the CR moderator, and from some very savvy forum regulars. There are also links on the left side of the page, under "Related Information," for more on CR's comprehensive tire test ratings to aid research and fuel discussion.

Some of the questions and discussions are truly unique, such as how well do winter tires work at temperatures of 50 to 60 degrees below zero; which, naturally, leads to the question of will the car even operate at these outrageously cold temperatures. And there also was the forum user who discussed how useful snow tire chains are when traveling through the difficult terrain of the Panama rainforest.

Most of the questions are pretty mainstream and offer a barometer of what's happening in the trenches for consumers when comes to tires. Here, CR tire test engineers learned first-hand of some of the quick wearing performance tires that we recommended, and as a result CR now does vehicle road test wear evaluations to provide tread life ratings. We, that is, the tire test engineers, witnessed the complaints of fast wearing runflat tires on Toyota Sienna AWD models, so we're now in the midst of a wear test program to share first-hand information that we'll write about in future blogs.

We also learned that consumers are not often aware that their new cars may come with runflat tires on it and don't have a spare tire; that the car has summer performance tire that offer virtually no grip in cold wintry weather; or the performance tires on their new family sedan will wear out quicker and are more expensive to replace than the tires on their previous car. Tire technology is changing to keep pace with new cars, and we keep on top of all the news and latest products in the industry.

We also recognize that tires are more expensive to buy; come in larger wheel sizes; and have higher speed rating grip and cornering limits. These innovations allow cars to handle safely and securely at levels your old car (and tires) couldn't match. Our advice when buying a new vehicle: Ask about the standard tires and tire options available to be sure you get what you need.

CR tire engineers are always perplexed by how some consumers will buy an expensive car or SUV and then when it comes time to purchase replacement tires will quibble about tire cost and even consider using lower speed rated tires than recommended just to save a few bucks.

Remember: Tires are the only thing between you and the road. The wrong tire can make a good car perform badly. Don't get caught. Use CR's information on how to choose a tire, read our test reports, and ask questions on TireTalk. We'll see you there.

-- Gene Petersen