vlad_a

What is UTQG rating on your tire? It will be stamped on the sidewall.

NateJG

What's the science behind the recommendation/insistence to shave a tire to match - on an open-differential system?

The 19" tire that came on my RXh has a new diameter of 29.2 inches. The tire starts out life with 10/32" of tread - with 8/32" legally usable.

Assuming that when the tire is worn down 8/32", the tire will then be 1/2" less in diameter (8/32" from the top; and 8/32" from the other side - since whe're dealing with diametert and not rolling radius) which means that the tire when legally worn out is then 28.7 inches in diameter.

That then becomes 98.3% of what the tire measured when new.

The 713 Revolutions per Mile when new then becomes 725 Revolutions per Mile.

So, for less than the maximum of just under 2% difference in size the recommendation is to throw away over half of the new tire's tread life?

I'm not convinced that there's enough difference to matter.

Would someone please point out the error in my thinking?

sktn77a

iTrader: (2)

Costco are notorious for pulling this scam with AWD vehicles. Next time tell them that the car goes round corners...... oh, wait, that's what a differential is for! And for the reasons stated in the post above, your imperceptibly different tire sizes puts a lot less stress on the diff than going round a corner!

fastnoypi

Good point from NateJG regarding the open differentials in the RX. As noted in my earlier post i've had to shave a tire to match my others in my subaru. I recall when i had my old Audi A6, the manual also mentioned that tire tread thickness has to match. According to some further research it appears the differential types that Audi and Subaru uses is a clutch pack type which can get damaged over time if you don't shave a tire. I've erred on this caution when i picked up my first RX300 and newer RX350.
.
The open diff type found in the RX's and Highlanders per the other Toyota forums should have no concern to put a new tire.
Good to know this now in the event i have a tire situation in either of my RX's.

jfelbab

That's 3/32nds used and something like 3/32nds to 5/32nds remaining depending whether you choose to replace at 4/32nds or 2/32nds. In the Tire Rack article linked previously, the stopping distance on wet pavement is substantially longer at 2/32nds. If you live in a rainy area this could be important.

This would mean you had between 50% and 62% tread life remaining if just using math. Yet there is more to this than just math. If you don''t rotate your tires regularly, if you don't check the tire pressure often or you have alignment or suspension issues your tread will wear unevenly shortening that tire life. I use an inexpensive tread depth gage to check the tread depth across the tire and at various spots around the tire to see that the tread is wearing uniformly. I check my tire pressures monthly. I have the tires rotated at every service. Finally I replace tires after 6 years regardless of tread depth. If you look to a used tire to fix your issue, check the tire date code and try to not buy old rubber.

Tire date code: http://www.tirerack.com/tires/tirete...151118160109:s

goodrx350

Treadwear - 440
Traction - A
Temperature - A

vlad_a

That means your tires are rated for 31,680 miles. You already put 25K on them. Another 7K miles remaining. At that stage, I would do all 4.

fastnoypi

How did you conclude that mileage rating from the UTQG? Michelin states the OP's model is warrantable up to 55k miles.

vlad_a

Warranty mileage is meaningless. It does not cover wear, so they could extend it to 100K if they wanted to - the tire won't last that long anyway.

Wear is measured in the UTQG Treadwear Grade. 7,200 miles (Total Test Mileage) * 440% (UTQG number) = 31,680 miles.

jfelbab

The Treadwear rating is a number based on a vehicle test where tires are compared to a control tire. The rating is based on a percentage in projected wear life. So a tire rated at 400, projected twice as far as a tire rated at 200. Since there are many factors that influence wear, such as vehicle speed, road surface, climate, vehicle alignment, and driving habits, these ratings are merely an indication of the wear characteristics of the tire.

7,200 is the distance of the test track used not the specific mileage one would expect based on a UTOG rating.

fastnoypi

Unless I'm interpreting it wrong, it looks like Michelin is covering wear.

"These MICHELIN® tires carry a 55,000 mile limited warranty in addition to the standard materials and workmanship warranty for treadwear or mileage."

UTQG rating is pretty much useless unless you want to compare compound softness to another like purpose tire. However you can generalize a higher UTQG numbered tire should last longer than lower rated UTQG number tire.

Kostyan

I think at 25k mi or 7/32 of depth, you are at approx 50% tire life, so it won't break anything if you replace just one tire.

For AWD applications, more drastic differences may cause problems, but this is exactly one of those where you should not have to replace all 4 tires.

ericsan13

At what point does the UTQG rating * 72 consider the tire to be done? At 2/32 or 0/32?

jfelbab

The UTOG rating says nothing about minimum wear. It is a government regulated test procedure to help consumers get an general idea of tread wear, traction and heat.
http://www.tirerack.com/tires/tirete...151119213904:s

The accepted minimum tread depth is usually quoted at 2/32nds but based on wet driving condition tests, 4/32nds could reduce your highway stopping distance by 100 feet. That could keep you and your family out of an accident and possible injury. If driving in snow, the most widely accepted minimum is 5/32nds.

nelsonsc

You started at 10/32 and now have 7/32. That's 70% of new. If you assume usable life is done at 2/32 then you are at 5/32 left or 50%.