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I went to a shop to get two new front tires, as the ones on the rear have about 15K miles worth of good, even threads left. The shop recommended that I replace all four tires, the offered logic being "on all-wheel drive vehicles mismatched tires could have catastrophic handling difficulties". I said thanks, but I'll just take two. Then the manager comes to his salesman's aid and says, "we would be held liable if you had an accident", implying it's four or none. So I shrugged and walked.

I think it was pure sales pressure BS aimed at increasing their bottom line,
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Oops, tapped Submit instead of Preview. My question was going to be, is there any merit to the tireman's claim?

Thanks

RayB
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I found article. According to them mismatched tires could lead to drivetrain problems.
Some car brands more sensitive than others.
https://www.souzastireservice.com/tires-101/tire-matching-aw...

Good Lord! If true that’s a good argument for not buying an AWD vehicle. What about mismatched air pressure in the tires?
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Thanks for the link. The warnings are not as dire for all brands. Subarus are singled out as having less tolerance in matching tires, while others are subject to the manufacturer's recommendations. My owner's manual states only that replacement tires should be type 103T, and does not specifically state the requirement of replacing all at once.

RayB
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I think you were treated to a bait and switch sales tactic.

You usually can avoid this problem with regular tire rotations. Once a year. Every 20K miles or so.

They have been making this sales pitch ever since radial tires replaced the old bias belted tires. But then what happens if you have a spare tire in the trunk and need to use it.

I suspect its mostly sales pitch for most careful drivers. Maybe a concern at high speed or on difficult terrain.
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It’s absolutely essential to check your vehicle’s owner’s manual to see if it recommends replacing all four of your AWD tires at once. Look in the tires and transmission sections. Or call your auto dealer for your make and model and ask the service department.

Ignoring this advice may result in costly damage to some of the most important driving components of your car, like the transmission. Any reputable tire dealer will follow what the car maker says to do. And almost all manufacturers agree that you should replace all four.
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I think it was pure sales pressure BS aimed at increasing their bottom line,


https://blog.tirerack.com/blog/todds-tire-decision-guide/rep...

It's a legitimate concern, although not exactly safety related or increasing the bottom line (margins on tires are very small compared to most other auto repairs/parts). Many tire wholesalers offer a shaving service to match the tread on one tire to the rest rather than replace all 4.
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We WOULD be held liable is not necessarily accurate. They COULD be held liable possibly.

If the front and rear tires are 1mm different in diameter, it's not going to suddenly snap your car in half and cover the highway in blood. Depending on the design of your 4-wheel drive system, it could result in very slightly more heat being generated in a viscous coupling, or a bit more pressure being put onto gear teeth and slightly more tire wear. Worst case would be in something like a Jeep Rubicon where it's got completely mechanical drive and both sets of axles can be fully, mechanically locked, and you're driving on concrete with pretty sticky tires. In THAT case, it would eventually wear out or break something, and could cause the car to drive wonky in the meantime.

But there is a chance - in our overly litigious society - that some idiot could have an accident and sue the company that sold him tires. So they've got a corporate policy not to fit them piecemeal. And sure, if it happens to work in their favor with regard to sales, they certainly aren't going to be motivated to back off of it. They could probably do what you want, and have you just sign a release that says they've warned you, but if it's helping their sales they aren't motivated to allow that.

I know several larger, chain type stores do this. But there are plenty of smaller local shops that will do whatever you ask them to do.

xtn
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How does a 4 wheel drive vehicle get uneven tire wear front to back. Clearly this vehicle is driven mostly in 2 wheel mode with 4 wheel used only occasionally.

4 wheel drive may not have been a good choice for this driver.
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How does a 4 wheel drive vehicle get uneven tire wear front to back. Clearly this vehicle is driven mostly in 2 wheel mode with 4 wheel used only occasionally.

4 wheel drive may not have been a good choice for this driver.


I rarely use 4wd in my vehicle but I still like the choice I made.

PSU
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What kind of car is it?

With part time 4WD (Transfer Case) you want the tires to be the same diameter since the front and back tires are rigidly locked together at the transfer case. Having them different diameters strains the transfer case, because if the fronts are rotating slightly faster than the rears, something has to give. This also happens when going around corners, so you never want part time 4WD on dry pavement. Snow, mud, and dirt only.

With all wheel drive the transfer case slips, so it should not be that big of a deal. But I imagine compensating for the front and rear different RPMs all the time could cause things to heat up a bit to much.

I would replace all 4. Cheaper then fixing the tranny, transfer case, or both.
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"What kind of car is it?"

It's a 2004 Chevy Equinox AWD I bought used from a friend six years ago and had all four tires replaced at the time. It's never been off the road, and I don't race it. We had since put 36K miles on it, and whereas the rear tires look near-new, the fronts had worn down to the warning strips.

Today I had the front tires replaced, and while on the lift I measured the circumference of front vs. rear tires. As it turns out there is less difference between the new front and the rear than there was between the old front and the rear, except now it is the front that's larger by a fraction. Handling is noticeably smoother, and the ride cushier. Driven at moderate speeds as we do I don't expect any problems out of this.

Thanks for all the responses.

RayB
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How does a 4 wheel drive vehicle get uneven tire wear front to back.


Really? 4-wheel drive does not magically mean that all four corners will experience the same weight loading, the same camber and toe setting, the same scrub during turns, the same applied torque, the same air pressure, the same temperature, etc., etc., etc.

There are a LOT of factors related to how much a tire wears besides just whether or not they are driven.

xtn
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We had since put 36K miles on it, and whereas the rear tires look near-new, the fronts had worn down to the warning strips.

Do you rotate your tires, front to back? You should. I do mine every 10,000 miles because it is easy to remember.
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Do you rotate your tires, front to back? You should. I do mine every 10,000 miles because it is easy to remember.

Bought my last set at Costco and they re-balance and rotate ~7,000 miles and so do
most tire shops around me.

George
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Bought my last set at Costco and they re-balance and rotate ~7,000 miles and so do
most tire shops around me.


Yep - they do.
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Your tires were 6 years old. Tread & matching isn't the only concern.

https://www.edmunds.com/car-maintenance/how-old-and-dangerou...

Age can also be an issue.
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""How does a 4 wheel drive vehicle get uneven tire wear front to back""

Easily on gravel roads. The front tires under the weight of the engine rarely spin. In contrast, rear wheels tend to spin more often as they lose traction with less weight for friction with the road surface.


c
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