[Chris65LeMans]

Along the lines of this other thread, but slightly different, I have a 2017 GMC Yukon that will need new tires soon. 2 of 'em have more life in 'em then the others, so I'd rather just buy 2.

Since I drive full time in "auto" on the 2WD/4WD selector (I only have 4WD when I need it), I figure this is fine. A google search turns up tons of pages promising dire consequences if I do this: but those all seem to be published by tire stores.

What are some of your opinions?

[The Champ]

I buy tires 4 at a time even on 2WD vehicles. Might just as well have 4 matched, equally worn tires for normal driving... If two are worn out, most likely the other two are getting old enough to replace anyway.

[77 TRASHCAN]

The factors of tire age are just as important as wear. There's several threads here, where the horse went dead, early.

the instinct to be wise with money is a good thing, but not concerning tires...JMO

[Chris65LeMans]

My car is a 2017, so tire age isn’t an issue.

[mgarblik]

The Yukon line has several different transfer cases. So not exactly sure what your truck has. If it has any mode that allows Full Time 4-wheel drive and you drive it in that mode, especially on the highway, that's when the transfer case is really working hard with mismatched tires. If you can drive it in 2-wheel drive mode, the mismatched tires are not near as much as an issue. Of course 4 nice, new tires with the same tread depth makes for a nicer driving truck.

[71GP76TA]

Originally Posted by Chris65LeMans

Along the lines of this other thread, but slightly different, I have a 2017 GMC Yukon that will need new tires soon. 2 of 'em have more life in 'em then the others, so I'd rather just buy 2.

Since I drive full time in "auto" on the 2WD/4WD selector (I only have 4WD when I need it), I figure this is fine. A google search turns up tons of pages promising dire consequences if I do this: but those all seem to be published by tire stores.

What are some of your opinions?

Why do you drive around in "auto" ? Why not 2WD? Isn't like you get snow and ice in LA..

[Sirrotica]

Tires never seem to wear out evenly, on my 1993 K3500 dually 4X4. I replace them when they get below 4/32 in. whatever position they're in. New tires are 11-12/32 when new. Conceivably I could have 8/32 difference between a new tire and a used tire, or 1/2 inch in total diameter, or 1.57 inches in circumference. I guess if money is no object than buying 6 tires at once is just fine, but I'm far from wealthy. At $200 per tire that's $1200 to even out all six tires, that's not in my budget.

This truck is part time 4 wheel drive and has the original transfer case and rear axle in it. It has IFS and I have replaced both CV axles in it because the boots ruptured and lost all the grease. It has 270,000 miles currently. Only replacing tires as needed has had zero effect on the longevity of the drive components. 9200 GVW.

If you engage four wheel drive on a hard surface the lack of a middle transfer case will bind up the driveline and it will jump and hop when turned because of driveline wrap up. Any 4x4 without a center differential does the same thing if the tires can't slip on the road surface. All the older 4X4s had a warning to not engage the front axle on hard surfaces as damage may result. It's been that way ever since I was old enough to ride in a Jeep.

I also own a 1995 C3500HD dually 2 wheel drive truck that has had tires replaced as needed by the former owner. I know that they only replaced tires as needed because there are 3 different brand tires on the truck. The truck takes 225/70r x 19.5 tires. They retail for roughly $250 to $300 per tire, or $1500 to $1800 per set. That doesn't include labor balance and taxes, you could easily be right in the neighborhood of $2000 for 6 new tires. 230,000 miles, all original running gear. 15,000 GVW.

Last truck is a wrecker, 1988 IH S1600 dually 2 wheel drive, ex U Haul 24 foot van shortened frame to accommodate the wrecker body. It takes 245/70R x 19.5 tires. It currently needs 4 drive tires, the fronts are used, but still good. These tires retail for $350-$400 per tire. For just the 4 drive tires I could spend between $1400 to $1600 before mounting, balance and taxes. 18,000 GVW. Original running gear.

From this list of my trucks, I will replace tires on an as needed basis.

My cars,

2008 Vibe FWD, usually get 4 tires at a time.

2005 GTO RWD, rears wear out at 2 to 1 compared to the front, I have wider tires in the rear, so they cannot be rotated. Replaced on an as needed basis.

1999 Pontiac GP FWD, last time I went from 15 inch wheels to 16 inch wheels, so it got 4 tires, but I still have saved 2 of the good 15 inch tires, they will probably go on my single axle utility trailer.

If the tires are below 4/32 they get replaced, not necessarily all at the same time.

I guess an AWD vehicle is out of the question for me, because I will not replace all 4 tires, because one blows out. I won't replace all 4 tires to keep the PCM happy, and the current transfer case differentials are obviously poorly engineered. A differential is supposed to be able to make mismatched speeds not harm the component, evidently the engineers can't make them work as intended.

This is the definition of a differential:

The differential is a device that splits the engine torque two ways, allowing each output to spin at a different speed.

The differential is found on all modern cars and trucks, and also in many all-wheel-drive (full-time four-wheel-drive) vehicles. These all-wheel-drive vehicles need a differential between each set of drive wheels, and they need one between the front and the back wheels as well, because the front wheels travel a different distance through a turn than the rear wheels.

Why is it that current differentials don't work as intended? They absolutely aren't working as per definition, and doing the job of splitting torque to front and rear axle revolving at different speeds, and not harming the driveline components. Gotta have tire circumference within 1/3 of 1%, or they disintegrate. Total junk designs that do not work as differentials.

There will be no AWD vehicles residing in my driveway, unless they build a real differential for the transfer case, that will split torque between unmatched speed axles, and wont disintegrate.

[72projectbird]

I just replace the two that need it, doesn't matter if it's a 4x4/AWD.

[lust4speed]

My wife's Yukon XL is older, but bet it's the same system. For others, the computer senses different driveshaft speeds and locks the front wheels if needed when running in Auto. It's not an all-wheel drive and simply chooses between rear wheel drive and locked 4-wheel drive.

There's a lot of weight on the back of our Yukon and most of the time the only reason it goes out of 2-wheel drive is to exercise the system when I borrow it. The last 1/8 mile portion of our 1 mile dirt road is 12% and the Yukon never spins in 2-wheel drive. I always have to lock up my 2500HD long bed in 4-Hi for the last stretch or I would quickly wear out my rear tires.

Anyway, back on the subject, I'm wondering if the system wouldn't think the difference in front/rear driveshaft speeds with old/new tires might not engage 4-wheel drive when not needed or wanted.

[The Champ]

Originally Posted by Chris65LeMans

My car is a 2017, so tire age isn’t an issue.

Date codes on tires may change your mind on age. Don't assume the tires are from 2017.

[Chris65LeMans]

Date codes 30 and 3117. Newer than I expected. One of the better ones is from mid 2018. (Ran over the pin in a parking block and ruined a tire. )

[GTOnly70]

Originally Posted by Sirrotica

2005 GTO RWD, rears wear out at 2 to 1 compared to the front...

Interesting, my 2015 Challenger RT is the same way.

[Sirrotica]

Originally Posted by GTOnly70

Interesting, my 2015 Challenger RT is the same way.

Funny how that happens..................

[71GP76TA]

Originally Posted by Sirrotica

Funny how that happens..................

My '05 GTO and '09 Challenger R/T had the same problem and I don't understand why.

[Chris65LeMans]

Originally Posted by Sirrotica

Funny how that happens..................

I’ve got a lead foot, so I’ve had that problem with every car I’ve ever owned. (With the front tires on the fwd ones, too.). Which is why we’re talking about this with my Yukon, too.

[Formulabruce]

Leave it 2wd or auto 4wd, and buy 2 tires same size And Pattern. The sensors compensate for rotation on corners already. Don't use 4X4 unless off road or on snow. You will be fine.

[Chris65LeMans]

That’s what I was thinking. Thanks, all. When I had to replace one tire, I searched the owners manual and found no mention of it.

As for the auto 4wd - it’s an XL, the biggest on the road, with a 420 hp engine. When taking off briskly from a stoplight, especially around corners, the momentary 4wd comes in handy.