Tires: Factory Ratings vs. Real World, treadwear rating, miles warranty

Question
Barry,

A question I've been kicking around for a while is how do various tire ratings compare in the real world.

For example, brand A has a treadwear rating of 600 and a temperature/traction rating of A/A.  The manufacturer offers a 60,000 mile warranty.  Assuming the owner of that tire follows the manufacturer's recommended inflation/rotation ballancing periods show I expect to get better life from that tire or Brand B which says it has a 450 Treadwear rating with a traction/temp. rating of A/B and an 80,000 miles warranty?

Answer
Richard,

Let me set some background:

Most tire wear occurs in the cornering mode, so the amount of miles you get mostly depends on how many turns you make.  So mileage warranties are more an insurance policy than anything else.

But the treadwear rating is based on a government mandated test, and if the rating is based solely on the results, then you should expect a tire with a 600 rating to wear twice as long as one with a 300 rating.

But there is a little more to this:  Because the test is supposed to be compared to an SRTT (Standard Reference Test Tire) and the test requires 2 identical vehicles with the tires swapped regularly between the 2 vehicles, you have to get a vehicle that is compatible with the SRTT - and for some types of tires that is impossible.  So the government allows the test to be run such that you can trace the results back to an SRTT - and that allows some fudging to go on.

Plus the marketing guys want to "position" all their lines of tires in a certain way, so while they can't over-rate a tire, they can certainly under-rate it.

So you have to take the ratings with a grain of salt.  There is some directionality, but accuracy is not there.