Ratings Formulas: The Math NHTSA is Doing to Help You Make Better Tire Choices

Tire Efficiency Consumer Information BETA

This summary of the agency’s reasoning lets you react to specific paragraphs. For example, to react to the third paragraph, click either “Paragraph 3.” or the on the right margin. To see what others have said, click either the phrase “x comments” or the beside it To see summaries of other issues in the rule, go to the Rule Map.

Ratings Formulas: The Math NHTSA is Doing to Help You Make Better Tire Choices

Dig In

Ratings Formulas: The Math NHTSA is Doing to Help You Make Better Tire Choices
Moderator – 10:00 am, November 14, 2009

The proposed new consumer tire label would use three 0-100 ratings scales because NHTSA’s consumer research showed people found these easiest to understand. Behind the rating numbers are complex formulas that rest on data collected by NHTSA and the California Energy Commission, which is working on a similar tire consumer information program.

The “Fuel efficiency” rating is based on measuring the tire’s “rolling resistance force” (RRF) – the amount of force required to make the tire roll on the road surface. The lower the RRF, the less energy (fuel) required to move the tire. The formula factors in a comparison between the particular tire model’s RRF measurement and the best and worst RRFs of all tire models tested. NHTSA calculates that every five points on the scale translates to fuel savings of about 3 gallons of fuel per 10,000 miles per 4 replacement tires.

The “Safety/wet traction” rating measures how well the tire performs on wet concrete and wet asphalt. Again, the underlying formula factors in testing data from multiple tire models. Information about traction performance is already available on every tire: it’s part of the code of numbers and letters stamped into the sidewall. But most consumers don’t know about, or understand, the code, so NHTSA hopes that the 0-100 rating on the new label will make the information more accessible.

The “Durability” rating measures how long the tread should last. Like traction, treadwear information is already stamped into the sidewall code. NHTSA proposes to convert the existing measurements to the basic 0-100 scale. The durability scale is relative: A tire with a durability rating of 20 should last twice as long as one with a rating of 10.

What do you think? Would a label like this help you to make a more informed decision when purchasing tires?

HAVE YOUR SAY by replying below, or DIG IN to the rating formulas the new label.

Tags: upcoming

It looks like you are using Internet Explorer. During the beta test, Regulation Room will work best with Firefox, Chrome, or Safari. We will have multiple browser compatibility for the first "live" rule, which is scheduled for early 2010.

NYCMuscleman18

10:16 pm November 14, 2009

I think standardized ratings are a problem for me because the difference between 40 and 100 re. efficiency will almost never be the same as the difference between 40 and 100 re. traction. Depending on the distribution of each measure, the difference could be drastic. So when I’m evaluating all three and considering the tradeoff, I don’t have as much information to compare.

8:45 pm November 14, 2009

I don’t know how to measure the tradeoff between traction and fuel efficiency, and the lack of real units probably won’t help. I assume NHTSA makes it illegal to sell tires with dangerously low traction, but what’s the difference between a score of 40 and a score of 100? Without that information, I have more information when I make my decision, but I’m probably not using that information well. en

Moderator

9:50 pm November 14, 2009

Hello NYCMuscleman18,

You make an interesting point about the qualitative and quantitative differences in scoring. If NHTSA created a standardized metric on which all tires would be measured, some tires would receive a higher score, perhaps a 100, and other a lower score, such as 40. Would that be enough information that the first tire would serve the consumer better for fuel efficiency than the second tire, or would you prefer a more concrete quantitative approach?

You must be logged in to post a comment.