Tires Q&A: Tire rolling resistance

In our ongoing series of Q&A blog columns, we will highlight common and interesting questions posted to our Car forums, with answers from our automotive experts.

Question: I bought four Yokohama Avid TRZ tires just two weeks before the 11/09 Consumer Reports issue arrived. I'd read reviews on the internet but none addressed mileage. As I drive an ‘04 Prius, mileage is very important. I had been trying to figure how new tires would drop my mileage a very noticeable 10 percent (from 53.3 to 48). Had I only known the tire ratings were coming I would gladly have waited and would definitely have different tires today.

Answer: I’m sorry the report did not reach you in time of your tire purchase. Until the State of California or the federal government comes out with rolling resistance regulations and ratings, your only sources for rolling resistance information on tires are from manufacturers’ claims and Consumer Reports. Our testing is comparative among the models tested.

Yes, you could have purchased a more fuel-efficient tire, but the Yokohama Avid TRZ is average among all season replacement tires for rolling resistance. Some were better--such as the top-rated Michelin HydroEdge, and the Toyo Versado LX. One point to consider when replacing tires: As tires wear out, you’ll likely see improved fuel economy since the tires will have less rolling resistance as the tread (mass) is removed from the tire. Installing new tires, identical in brand and model as those removed, and you likely see a reduction in your fuel economy. The new TRZ tires should become more fuel efficient as the tires wear. Also, keep the tires properly inflated and check them monthly to get the optimum fuel efficiency.

To see full details on the tire models we tested, check out our Ratings and recommendations (available to subscribers). In addition to our updated Ratings, all site visitors can access our free buying advice for tips on getting started, types of tires we test, features that are important in making a tire purchase, and general tire care. Also, be sure to check out our TireTalk forum to interact with our tire engineers and other drivers.

—Gene Petersen 

Tires Q&A: Tire-testing vehicles

In our ongoing series of Q&A blog columns, we will highlight common and interesting questions posted to our Car forums, with answers from our automotive experts.

Question: Has CR tried using different cars, but same size tires to see if the relative ranking would change dramatically?

Answer: Our tests are designed to judge tire performance on a comparative basis. Our goal is to use a popular and suitable car and appropriate tire size that also best represents the segment we are evaluating. Hence, we use one car or truck as the test calls for.

From our experience, a car’s natural abilities in terms of handling and ride comfort would influence the results, but it would be an offset in the comparative ratings between one car model to another. Also, differences in vehicle weight, wheel alignment, and drive-wheel configuration could affect a number of tests like snow traction, ice braking, and hydroplaning resistance. But, again, the comparative results should be maintained. The same holds true for our tread life test that’s done on like vehicles under identical conditions and is strictly a comparative test. Rolling resistance is the only test done without a car, performed on a dynamometer, so there is no vehicle effect.

More recently we have seen stopping distance reversals of tire models when used on different cars. This generally happens with tire models that are somewhat close in braking performance, and our data suggests a grippy tire is generally good on a wide variety of cars. But today’s cars have ABS brake systems tuned to a specific peak friction characteristic. To judge the tire’s peak level of grip we now do a “best effort” stop on dry and wet surfaces. A best effort stop has the driver modulate the brake pedal effort to get the shortest stop without wheel lockup, evaluating each tire model to its own peak friction level.

Comparative testing works well if you can remove or compensate for the vehicle effects as we strive to do. Publishing actual data would be misleading because it applies to the specific vehicle used.

Ratings, recommendations and buying advice on car, truck and winter tires, see our tires section.

—Gene Petersen  

Tires Q&A: Run-flat tires for Corvette?

In our ongoing series of Q&A blog columns, we will highlight common and interesting questions posted to our Car forums, with answers from our automotive experts.

Question: My first Corvette has Michelin Pilot Sport A/S Plus. I’m considering using the same tires but in a run flat, but I hear bad things about them. Any feedback would be appreciated.

Answer: In short, the virtue of a run-flat tire is extended mobility with no need to worry about being stranded with a flat tire. If you have my luck, the tire will go flat on a rainy, cold night over a dangerous section of road--and you don’t get to choose when a tire goes flat. Run-flat tires can handle a puncture or road-inflicted damage and allow the driver to make it to a service station or final destination. That’s the payoff of having run-flat tires.

Our experience is that some applications work better than others. The Corvette C5 is a perfect candidate for run-flat tires as there’s not much room for a spare tire, let alone room for tossing in a full-size flat tire inside the car. Run-flat tires are stiff by design to support the weight of the vehicle with no air pressure. For the Corvette, which uses stiff, low-profile ultra high performance tires, a run-flat is not much of a trade-off in terms of ride comfort and handling, even when it goes flat. Also, the Corvette was designed to accommodate run-flat tires, so it should be your first consideration when making a new tire purchase.

See our run-flat report to learn more about on the pros and cons of run-flat tires. For Ratings, recommendations and buying advice on car, truck and winter tires, see our tires section.

—Gene Petersen 

Tires Q&A: Problem solving irregular wear

In our ongoing series of Q&A blog columns, we will highlight common and interesting questions posted to our Car forums, with answers from our automotive experts.

Question: My Mazda RX-8 is showing tread wear on the outer edges of the tire. Wheel balance, right? Wrong. I paid $50 to find out that all the wheels are within specs. I consistently keep the inflation between 32-34 lbs so that can't be it. The shop guy said "bad tires." They are original Bridgestone Potenzas. Could he be right? I don't know where to turn next.

Answer: Tire wear issues like that mentioned above are all too common and often the blame goes to the tire manufacturer if there is no apparent easy answer. That’s too bad since it can be avoidable most of the time. Most experienced tire dealers can diagnose the problem just like a doctor does with a patient – mostly by observing and narrowing down the possibilities.

In this case, the tire wear pattern tells the story. The fast outside shoulder wear suggests a wheel mis-alignment. The owner said that the tires received an alignment, which was deemed in-spec but not on-spec. Often that might not be good enough for some cars and the owner and consumers alike should request that wheel alignment be adjusted back to the middle of the alignment specification or as close as possible. In other words, sometimes “close-enough” isn’t good enough. The RX-8 owner isn’t alone. We just recently examined a police cruiser that had a similar wear problem. The officer had the cruiser checked for alignment and was told it was within tolerance but not to the exact specification. Ironically, the alignment shop told the officer that the tires were probably the problem and replaced them. Guess what? The new tires were starting to wear like the old ones. We told the officer to have the wheels re-aligned to the exact specification and to have the shop check for any worn suspension components while they were at it.

Bottom line: Sometimes you have to be persistent. The red flag in both examples was that the alignment was checked, but the shop didn’t put the effort into re-aligning the car to the exact specification. Look at your tires, particularly their wear, as they can tell the story.

—Gene Petersen

Tires Q&A: How to choose the right tire for a Honda Odyssey

In our ongoing series of Q&A blog columns, we will highlight common and interesting questions posted to our Car forums, with answers from our automotive experts.

Question: I'm looking for some advice about tire sizing. I'm very interested in using the Michelin HydroEdge tires on my 2003 Honda Odyssey van. However, the size available for my van (225/60R/16) does not meet the load rating requirement.

I've noticed a lot of people are using this tire on the van over at TireRack, but I haven't seen any mention of the sizing. If I were to go up to a 235/60R/16 I would meet the load rating.

My question: Will there be any negative consequences of moving to a slightly wider tire? Perhaps lower mileage?

I'm also interested in the Goodyear Assurance TripleTread but the same issue applies for this tire.
 
Any good advice for choosing tires for this van? I'm looking for something that will last a good while and be very good in the rain.  

Answer: This issue is to swap-out Euro-Metric tires for P-Metric tires on the Honda. The Odyssey came with Euro-Metric tires, also called “Hard”-metric tires by some. This size designation is common in Europe, whereas in the U.S. a “P” precedes the size designation. The two size designation systems are similar, but not the same, adding to the confusion of making a tire purchase.  

In the case of the Odyssey, replacing the Euro-Metric original equipment tire with the same “size” P-metric version would result in load capacity shortfall of 44 pounds. (The load capacity and load index, a code that coincides to the load capacity both can be found on the tire’s sidewall.) Multiply that by four tires and the load capacity in down 176 pounds.   Most tire retailers may sell the tire in the two designations interchangeably, but tire manufacturers won’t recommend switching. Our advice when buying new tires is to follow the recommendations made by automobile manufacturer by replacing tires with the same size and load index as listed on the tire placard. The placard is usually found on the door jamb, under the fuel fill cover or in the glove box of most cars. With this knowledge, you can find a tire that best meets your performance and budget needs in our ratings.

—Gene Petersen

Before buying, be sure to consult our car, truck, and winter tire ratings and buying advice. And check out our new, interactive tire ratings tool.

Q&A: Am I better off buying a used car?

Am I better off buying a used car?

Buying a late-model used car instead of a new one can save you thousands of dollars over the first five years of ownership, assuming it has low mileage and modern safety features. That's because it has already taken its biggest hit in depreciation. If a car hasn't been well maintained, its reliability and value are wild cards. Before you buy any used car, ask a qualified independent mechanic to inspect it.

See our list of the best and worst used cars to find a reliable model.

Q&A: How can I protect myself from a failing dealership?

How can I protect myself from a failing dealership?

When a dealer has folded, some car buyers haven't received an expected rebate. Or the dealer doesn't pay off as promised the loan balance on a trade-in, leaving the consumer holding the bag for a vehicle no longer owned. Take these precautions:

• Use a credit card to make a down payment, order parts or accessories, or pay for service so that you can challenge the payment with your card issuer if a failing dealer doesn't come through.

• Try to pay off your loan before you trade in your car. Allowing a dealer roll it over into a new loan is a bad financial move.

• If a dealer has agreed to fix something or provide a service or accessory for your new car, make sure it's done before you take the car home. If you get caught short, contact the automaker's customer-service department to see what recourse you have.

See our new and used car guides for more information and advice on car buying.

Q& A: What if my dealer goes out of business?

If my dealer goes out of business, where should I service my car?

More than 900 dealerships closed in 2008, and more will probably do so. You don't need to take your car to a dealership for servicing; a good independent shop that specializes in your brand should be able to handle routine maintenance and repairs. But you need a dealer for warranty and recall work. If there's no other dealer in your area, call the automaker's customer-assistance number in the owner's manual to find out where to take your car. Often, warranty repairs can be performed at other brand dealerships linked to the same automaker. Sometimes an automaker will arrange for dealers of another manufacturer to handle the work.

See our recent blog on what to do if your dealer closes.  For more information on servicing your car, see our report on how to save money on maintenance.

Q&A: How can I get auto financing?

How can I get auto financing?

The financial arms of some automakers have pulled back on car loans. But many banks and credit unions will lend to buyers with good credit. Compare rates with those available through a dealer. To boost your credit rating, reduce debt, avoid late payments, and fix errors in your credit reports. Note that many lenders now require down payments of about 20 percent.

See our car buying advice section for buying and financing advice, calculators, and more.

Q&A: How long can my car last?

I want to keep my car. How long will it last?

A reliable car, if well maintained, can go 200,000 miles or more with few if any major repairs. But it's time to part company if the car needs repairs costing more than half its value, if it seems likely that the car could leave you stranded, or if its structural integrity is compromised.

Learn how to make your car last for 200,000 miles and visit our 200,000 mile club forum to discuss tips for making your car go the distance.