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  

Comments

[Richard Adin]

Your comment about how you test tires makes me wonder about following your advice. I own a 2006 Subaru Outback LL Bean (which we love; this is our 4th Subaru). I had to replace the tires last week and so went to your ratings. Based on your recommendations, I purchased the Goodyear Assurance TripleTred. But based on the above comment, I'm not certain I bought the right tire for my car. Did I? I ask because I'm wondering whether they are the appropriate tire to buy for an all-wheel drive vehicle as opposed to a front-wheel drive vehicle that you probably test it on.

[Michael W.]

You said, in part:

"But today’s cars have ABS brake systems tuned to a specific peak friction characteristic."

Can you elaborate on that comment a little? It makes me think that I won't get better stopping, in an ABS actuated situation, even if I upgrade the grip of my factory tires with better after-market tires. Is that true?

[Alan Rogers]

I own a 2008 Mini Cooper (great car!!!) and recently had a flat and had to buy new tires.
The Mini uses run-flat tires.
When I went to my local dealer, there was only 1 model of tire available, and they cost about $200 each (including mounting). They had to order special and I had to wait about a week.

The cost prevented me from buying all 4 tires. But I would like to replace the other 2 tires soon.

Could you please post some information on these tires? I dont expect a full review, but would like to know what's available and some information on the technologies.

Thank you.

[Dovidan]

I am purchasing a 2010 Subaru Outback Limited. I live near Seattle & my concerns are in order of priority: Traction & stopping on wet pavement, noise, comfort, handling, ice braking, & fuel economy. Your testing suggests that the Michelin Primacy MXV4 would be my best bet. The OEM tire size for the 225/60 R 17. The closest MXV4 size is 235/55R17. Any reasons I should not use this size?

Other than the MXV4 what would you recommend for my new Outback?
Thanks