Has anyone heard of not mixing new tires with old if they are 2/32” difference?

[4S50]

So, I ruined a tire in Death Valley, (punched a rock through the center of a BF Goodrich KO2). The Tread measures about 9/32. I was given a pro-rated refund for the damaged tire but the salesman refused to sell me one tire. He claimed that due to this being a 4x4 that the store assumes liability for damage to the 4x4 system due to the tires being mismatched in diameter (by 6/32, I think).
I Have driven 4x4 of all makes, and conditions, with many different tire sizes and combinations, as well as being a mechanic and do not believe this at all. I was unable to talk the manager out of this course and they wore me down and I bought 4 more tires.
Has anyone else heard of this and, if so, can you point me to the source?

Sponsored

 

[NachoRuby]

Can't they shave it down? I've had to have that done before on awd cars.

 

[jac04]

If it is their policy, I guess you have no choice. If it were actually important, it would be in the Owners Manual. I can't find anything in the manual other than:

 

[MrFahrenheit]

I've anecdotally heard of this along with shaving the new tire down to the existing tread depth. I have 5 tires and wheels and do 5 tire rotations. If I had to replace one I would probably find a shop to shave it down to match the others.

But I'm on your side with this one. If I had 30K miles on my tires and never used the spare then got a flat, am I now not allowed to use this spare tire because it has full tread depth?

 

[4S50]

Out of curiosity I measured the circumference of the Falken AT spare on the driver rear and the BF Goodrich AT on the driver front (both at the same pressure per my digital gauge) and then calculated the revs per mile-
DR- 640.80
DF- 641.29
.076% difference
I could maybe agree with this on AWD, but on a standard 4x4 it makes no sense. But, like Del Gue said in the movie Jeremiah Johnson, “Their rules is their rules…”.

 

[ShadowsPapa]

I've covered this ad nauseum in the tire rotation threads. You would see MAYBE up to 5 rotations differences in a mile. In other words, the larger tire would rotate only 5 times less than the others. It's not a big deal at all.
And that's a max difference, most likely it would be less. You have more differences due to other things and nothing breaks or wears out.

 

[CerOf]

It’s really only an issue with full time 4wd/awd.

on a part time t-case, no real issue.

If you’re concerned, just shave the one Tire. That is the acceptable method on an AWD vehicle. (And is recommended by Subaru for their vehicles)

 

[4S50]

So, I am seeing the consensus being that this is BS and no one can cite a valid source other than the mythical lawyer said it is a liability dodge?
thanks!

 

[jac04]

I certainly couldn't find anything in the Owners Manual about it. The tire store may have a "valid source", but it would likely be in the form of a company policy. You could always ask to see it, but I'm not sure they are obligated to show it to you.

If you feel you were taken advantage of, I would contact someone at the company, explain the situation, and ask if there is anything they can do for you. It never hurts to ask.

 

[Hootbro]

If it was an issue, they would put it in the owners manual.

My wife drives a AWD 2021 Honda Ridgeline and there was a note about replacing all 4 if possible but if not possible, replace front or rear in matched pairs.

 

[ShadowsPapa]

Back on my math->


A difference of diameter of .18" is a whopping gear killing 5.4 revolutions per mile difference. (he says sarcastically)

Seriously, that means if you have a tread depth difference of 3/32", which is .09", between old and new tires you will see a difference of revolutions per mile of maybe 6. (a diameter difference of .18 means .09 worn off the tread)
3/32" is about .09"
6 revolutions at the most difference. You can drive a mile on an ordinary road and have many times that difference in rotations per mile because of other factors.
So what I'm saying is if you have 3/32" tread depth differences, you can't even see the difference in tire speed if you watched them over a mile's distance. That won't kill any vehicle. If it did, you would have to never take any curve, imagine how a simple exit ramp would destroy your car as you'd have several times that difference in rotation speed just taking an exit and making a turn.

If concerned, shave it, but frankly, I'd bet that if push came to shove, a set of tires may have a natural difference in diameter you could measure, then take into account road crown, curves or irregularities in a road, other factors.

Sponsored