Tire pressure and diff wear

[JHZR2]

Is this really a consideration? I've read warnings of driving some awd systems with mismatched or improperly rotated tires. I'd imagine that pressure can make a bigger difference on circumference.

So two different pressures on a drive axle and what happens? Is the metal sufficiently hard and the adds sufficiently good that it just promotes more wear on one tire than the other? Or can the diff actually exhibit wear?

 

[RiceCake]

I think your tires would have to be considerably out of whack to really make a major enough change in tire circumference, but the difference exists. As tires heat and cool the pressure changes by a few PSI anyhow. If one tire is 15 though and the other is 45, you'll likely be causing an issue.

Realistically speaking every time you turn a corner, the tires have to spin at different speeds. The differential compensates for that but that change in tire speed can cause wear on different components because of the way it manages torque around the AWD system and whatnot.

It won't likely promote more tire wear, it will just make the AWD system work a little harder, which *may* contribute to excessive differential wear. Usually driving straight on the highway for hours on end with the differential having to compensate for different tire sizes can burn out the system.

It would be like doing a wheelspin on a posi and only one tire spinning. The diff has clutches to shift torque and if you're working against that, hard, and for a long time, you'll cause excessive wear.

 

[Kuato]

IMO if your tires are the same (make, size, pressure, miles on them), then you will have no issues due to manufacturing differences, and any differences will average out as you rotate.

I rented a Dodge Durango a while back with AWD. The fronts were different manufacturer than the rears, and on the highway running straight ahead got a "thrum thrum thrum" from the center differential working constantly. I test drove the same vehicle off of a dealer's lot, and no thrum.

AWD can be picky about tires, I know a guy that replaced two tires and had handling problems on his BMW.

Caveat: AWD = replace all tires at same time.

 

[Astro14]

For a regular differential, it's no big deal. For an LSD, it could be...depends on what the manufacturer says...

For the viscous coupling (center diff, essentially) on the Volvo XC, it's a very big deal. Maximum tread difference is 2mm, about 3/32", with identical tires required. Plenty of these cars on the used market with fried VCs because the owners didn't follow that requirement....

 

[chevydude]

what do you do if a tire gets damage and there is a 10000 mile difference between the rest of the tires. Is it ok to buy the one tire and still rotate as normal on front wheel drive. I ran into this on my car. the tire was the same brand and size that I replaced. should I worry about any premature wear on front end?

 

[Mopar618]

I drove a 2001 Honda CR-V for a few years that was AWD and had some issues with this topic.

At one point in time we had all tires replaced and had no issues whatsoever for a while. Eventually the tires were rotated, and suddenly the vehicle had TONS of feedback from the steering column, and on hard turns the tires seemed to suddenly start rubbing inside the wheel well. I never did have the time to figure out the issue, and it never created a hazard, but it could be why the OP stated they had read warning about "improperly rotated tires".

As for pressures on each tire from the axle, I can only envision it the way I do in my head, which makes sense to me at least.

The way I view it is, if you have four new, matching tires, they all have equivalent contact points at the same PSI. Therefore, the ride height and pressure of the entire vehicle should be balanced all the way across. If the PSI in one tire is lower than the rest, it's going to have a greater contact point on the road because the rubber is going to stretch out, instead of up, so you're already getting more wear on the rubber of that tire. On top of that, the vehicle would no longer be balanced in general and would literally be leaning in toward one corner, most likely putting more wear and tear on the axle components as well.

I have no clue if that makes sense to anyone else, but eh, just my two cents.

 

[Kuato]

Originally Posted By: chevydude
what do you do if a tire gets damage and there is a 10000 mile difference between the rest of the tires. Is it ok to buy the one tire and still rotate as normal on front wheel drive. I ran into this on my car. the tire was the same brand and size that I replaced. should I worry about any premature wear on front end?


Front wheel drive I wouldn't worry about it. If you are rotating 5 tires, just leave the newest one on, and don't put it into the spare position for a couple of rotations. If you're only rotating 4, then just rotate as normal.





Originally Posted By: Mopar618
I drove a 2001 Honda CR-V for a few years that was AWD and had some issues with this topic.

At one point in time we had all tires replaced and had no issues whatsoever for a while. Eventually the tires were rotated, and suddenly the vehicle had TONS of feedback from the steering column, and on hard turns the tires seemed to suddenly start rubbing inside the wheel well. ...


IMO on the Honda you could have avoided all the tugging by rotating earlier. When I lived in a suburban area, I rotated every 5k; if I didn't, the edges of the front tires would begin to feather badly. Now that 99% of my miles are highway, it's more like 15k or even greater.

 

[HerrStig]

Originally Posted By: chevydude
what do you do if a tire gets damage and there is a 10000 mile difference between the rest of the tires. Is it ok to buy the one tire and still rotate as normal on front wheel drive. I ran into this on my car. the tire was the same brand and size that I replaced. should I worry about any premature wear on front end?
Unless you play with tire pressure down to the pound, the difference in loading front to rear will result in different rolling diameters. There has got to be 1000 miles worth of slack in the system. Even four new tires won't wear at the same rate. How close do you have to watch them?

 

[rationull]

My Subaru (viscous coupling center diff, open front and rear diffs) recommends 1 PSI higher tire pressure in front vs in back. My assumption is that this is due to the effect the weight of the engine has on the contact patch size, but I don't know for sure.

I'd like to know how big a deal this is, too.