How are treadwear ratings determined? It’s not how you think.

By Andy Hollis
Jan 9, 2024 | SCCA, tires, 200tw, Vitour Tempesta P1, Treadwear Rating | Posted in Features | Never miss an article

Photography Credit: Rupert Berrington

What if we told you that a tiremaker could put whatever treadwear rating it wanted on the sidewall of a tire? And that the National Highway Transportation Safety Administration does no compliance checking on that rating?

How would you then feel about motorsports rule sets that require tires rated at 200tw or higher? It’s the dirty little secret of the tire …

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Colin Wood
Colin Wood Associate Editor
1/8/24 1:34 p.m.

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David S. Wallens
David S. Wallens Editorial Director
1/8/24 1:57 p.m.

Reading this made me reach out my first Solo rule book. Some cool tire ads in there.

Andy Hollis
Andy Hollis
1/8/24 2:05 p.m.

SCCA's first National Solo rule book...


David S. Wallens
David S. Wallens Editorial Director
1/8/24 2:07 p.m.

I dig the small-format SCCA rule books. 

Javelin GRM+ Memberand MegaDork
1/8/24 2:26 p.m.

Honestly reminds me a LOT of the early "fastest street car" days with McCreary clay track tires, retreads, and then the emergence of the Mickey Thompson ET Street, then the discovery of 12" wide "10.5" tires leading to the "10.5W" classes and "true 10.5" classes. 

Keith Tanner
Keith Tanner GRM+ Memberand MegaDork
1/8/24 3:13 p.m.

In reply to David S. Wallens :

The artwork on that 1972 is great. MGs and a Manx, along with an intrigued lady.

Andy Hollis
Andy Hollis
1/8/24 3:16 p.m.
Keith Tanner said:

In reply to David S. Wallens :

The artwork on that 1972 is great. MGs and a Manx, along with an intrigued lady.

I can't speak to the lady, but MG TD was a real fixture in early SCCA Solo.  And the Manx was popular in A-Modified, believe it or not.  Who'd a thought that was "unlimited".

RobMason New Reader
1/8/24 4:50 p.m.

In reply to Andy Hollis :

This is why I built my MGA to run autocross, and why I'm helping my dad to upgrade his MGTD to bring it out too.

AnthonyGS (Forum Supporter)
AnthonyGS (Forum Supporter) GRM+ Memberand PowerDork
1/8/24 5:35 p.m.

My dad managed automotive testing centers for about 25 years and most of the testing is tire or durability testing.  Not all of the testing is out of San Angelo.  I lived there 4 years while dad was in this business.  This article is good but not quite there.  The standard tire was a bias ply design that dates back to the DOT reg.  The standard tire had a tread wear rating of 100.  New tires last a lot longer have better traction and use way better tech.  

No one puts a standard tire on a car today.  I sure wouldn't drive a bias ply tire with 3 modern tires.  The mileage life of the standard tire is well documented.  The tire testers take temperature measurements, inflations, treadwear measurements and even use laser holography if the contract specifies it.  They generally run fleets of four cars for each test in case of a failure.  The contracts usually go to a set mileage.  The cars typically see 500 miles a shift, two shifts a day 5-6 days a week. Off-road tires get totally different tests but have highway tests too.  

I've known of test fleets based out of San Angelo, Ft Stockton and the San Antonio area (Devine).  I don't know who is still in business or not.  My dad hasn't been in that business since 2006 or so.  

Dad was also a regional SCCA guy in TX back when those rules were written.  

nealt GRM+ Memberand New Reader
1/8/24 6:33 p.m.

In reply to David S. Wallens :

I dig the small depth.

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