4 new ones to replace the ONE (1) with a staple on the edge of the tread/sidewall.
Tire monitor says R front low, stop in at Discount tire prior to getting on the freeway for a short trip. Watched from above as the tire came off and the area of the tire damaged was "chalked" . Thinking it looks really close to the sidewall, meaning not patch able by law. Suspicion confirmed as the worker came back and went straight to the computer, looking up options for replacement prior to giving me the bad news. I understand the need to have the same tires per axle. But now they are STRONGLY recommending changing out all 4 tires. As I am being told this, i was reading the same info on a small desk pad near the computer. Apparently the drive train could be damaged with mismatched tires. So is this guy / business shooting for sales quotas, or can mismatched tires cause problems down the road...
2015 GMC Terrain AWD

I'm no expert, but I have a hunch your AWD status plays a roll in all of this.

He's going for the cruise. Buy the same size and style and you will be fine.

It can screw up some AWD systems. Not sure about the Terrain's system.

The dealer may not be giving you the entire truth upfront but very well might be.

I drive an AWD vehicle and for the AWD, traction control and all the other safety features to work and in harmony with each other, the tires must be within a 1/4" in overall height otherwise the car systems start to go wonky.

Your choices are:

1. If the tires are close to a shallow tread then go ahead and replace them all.

2. If the other 3 tires have a lot of tread life but the new tire will be more than 1/4" difference, the dealership can shave down the new tire to match. This is not uncommon but the dealership doesn't make the money they would off a full set.

Buy the one tire that needs replacing and tell them to shave it to match the other side.

Assuming the other three still have decent tread life left.

dang, flashlightboy beat me to it

It is the awd. Depending on how worn the tires are it can make a huge difference. It might work but it might not, in fact I’ve been told it’s possible that it could break expensive parts like transfer cases etc. As far as discount is concerned they are absolutely going to suggest you change all 4 if you don’t and it breaks something it’s no longer there fault.

ETA they beat me to it.

quote:

So is this guy / business shooting for sales quotas, or can mismatched tires cause problems down the road...

If all the tires are fairly new, say, <20% worn, there is some wiggle room. In that case, replacing just the one tire shouldn't harm anything. If they are all significantly worn, one new tire, because its circumference is different, will cause problems with AWD differentials. The different rotation speeds will heat up the fluid or clutches (whatever it uses, if any) in the center and rear differentials and shorten their life. Similarly, you never use different sizes of tires on a RWD limited-slip differential. This is unfortunately the price you pay for AWD.

How worn are your other tires? If they’re quite worn, then I can see how one brand new tire among three worn ones could be an issue. However, if the other three are pretty good, I would just replace the other side of either the front or rear, whichever one has the hole, so that both tires in the front and both tires in the back have equal tread. As long as the tires are decent, it’s my understanding that it’s more important to have the same tread on the left and the right, but not so critical for the front and the rear.

BMW doesn't recommend tire rotations. So when the tires get a little wear you replace them.

Some AWD vehicles can get screwed up with too much difference in tread depth between tires. Check with the manufacturers specs.

quote:

Originally posted by doublesharp:
He's going for the cruise. Buy the same size and style and you will be fine.

All depends on tread depth of the rest of them.

My Audi was very very picky. Had fairly new tires and lost one. Replaced just that one and the AWD system was not happy.

I bought a used Explorer and they dealer I bought it from only replaced the rears. A no go it sent it into wonky land. Dealer put new fronts on and it was right as rain.

Do you have a full size spare? If so it should have full tread on it. Have them swap one of the partially worn tires with the tire on the spare. That leaves only 3 to replace.

Can you get a used tire somewhere. I used to buy them when I was young from Goodyear.

OK the above is truly and totally BS.
Every manufacturer of a modern FULLTIME AWD system has a specification for the amount of difference in rolling diameter that is acceptable for that system. Sometimes its a pain in the ass to find out what that measurement is, but there is a spec. At least in the cars I have owned and researched it is nowhere near an inch if we are talking circumference. On my particular current car it happens to be .3 inches, but as I said every mfg differs depending on the type of system. Do not assume different sizes are OK they are not. This is the price you pay for a good AWD setup.
The second type discussed simply is not relevant to this discussion and is also inaccurate. These are a part time 4WD system, you engage the 4WD system when you want it. Tire circumference simply doesn't matter as there is NO central differential. The issue of bind is not a tire size issue but one that there is no slippage anywhere in the system so torque can build up that has nowhere to go.
Correctly stated in such a system should not be used on dry roads.
Typically today these are part time 4WD trucks. It takes awhile to get serious problems if you are driving on dry roads but you eventually will, but you don't have to worry about small tire diameter issues.

Oddly the post I responded too is gone.
In any case I'll reiterate, find the spec difference allowable for your car and act appropriately. It will be a PIA to get the actual number out of GM, but it is available.
Conservatively I would do 4.

AWD I have always heard you replace all 4.

What does the owners manual say? Follow that recommendation.

I've got a 2013 Jeep Patriot & I had a tire dealer try to get me to replace all 4 tires saying because of the 4WD. My owners manual only recommends replacement in pairs. Needless to say that shop lost a sale & any future business.

Subaru strongly recommends replacing all four. Tires should be within about 5% of each other for computer. I have had to do it twice with about 35k on the set.

quote:

Originally posted by mrbill345:
What does the owners manual say? Follow that recommendation.

I've got a 2013 Jeep Patriot & I had a tire dealer try to get me to replace all 4 tires saying because of the 4WD. My owners manual only recommends replacement in pairs. Needless to say that shop lost a sale & any future business.

4wd and Awd are different systems. I believe most Awds are controlled be computer as to which wheels to send power to. Having different size tires messes with the calculations. Most 4wds don't lock the front and rear driveshafts together in high range hence the
per axle requirement.