AWD and changing less than 4 tires?

[Siciliano]

I have read that for ICE cars, changing just one or even two tires at a time (if they're just different brands, but the same exact size) could seriously mess with the car - alignment, transfer case, etc... There is quite the debate online about whether or not it's ok to do it (for ICE cars). I dealt with this with my Jag, but I haven't found anything regarding EVs, of course more specifically the M3.

Does anyone know if it messes with alignment or any of the components if you just change out one or two tires and they don't exactly match the others?? I'm just trying to think ahead!

TIA

 

[jrweiss98020]

Last time I had to replace a tire on my AWD Passat because of a tread separation, they (Les Schwab) told me I had to get all 4 new tires because they were worn more than 2/32" (NOT "down to 2/32"), and the different rolling diameter would damage the differentials.

Since the front and rear axles are not interconnected in any way on the M3, you can replace 1 pair. Put them on the back, because that is where most of the power (and regenerative braking) goes.

 

[camalaio]

The reason I've normally heard and experienced is related to traction control.

Different size tires less to slightly different speeds between the tires that aren't expected, which can trip traction control. Sometimes it just makes it touchier. For example, my smart car's traction system would light up going over speed bumps. But sometimes it can really cripple a vehicle until addressed.

Don't know how the Model 3 does with it. Many reports that you might lose regen until the car figures it out though (for much the same reason).

 

[grmdl3]

"Damage to differentials" seems like nonsense: difference in diameter would be akin to making a slight turn instead of driving absolutely straight. Are we supposed to only drive straight all the time to avoid that?

camalio's explanation is likely closer to the truth.

 

[stevegu]

"Damage to differentials" seems like nonsense: difference in diameter would be akin to making a slight turn instead of driving absolutely straight. Are we supposed to only drive straight all the time to avoid that?

camalio's explanation is likely closer to the truth.

Way back when I had one of the original (1983, in US) Audi Quattro Coupes (it was red, as they all were). To engage the 4-wheel differential lock, one had to be driving very straight as the system would wait until all wheel were turning in sync before engaging, and there was indeed a warning not to use the system on dry pavement unless one was going to drive very straight.

 

[grmdl3]

Way back when I had one of the original (1983, in US) Audi Quattro Coupes (it was red, as they all were). To engage the 4-wheel differential lock, one had to be driving very straight as the system would wait until all wheel were turning in sync before engaging, and there was indeed a warning not to use the system on dry pavement unless one was going to drive very straight.

Locked differentials are a different thing entirely, just as 4WD systems are different from AWD systems. Even a clutch-type limited slip differential is going to see minimal wear caused by a slight tire diameter difference.

 

[stevegu]

Locked differentials are a different thing entirely, just as 4WD systems are different from AWD systems. Even a clutch-type limited slip differential is going to see minimal wear caused by a slight tire diameter difference.

Yes, I know, but thanks for adding this clarification. Locking is for loose/wet/icy surfaces only; I just thought it was an interesting variation, and perhaps explains why somebody might give such an explanation.

 

[Gasaraki]

Minimum 2 tires. I always change all 4 tires at the same time.

 

[Siciliano]

Last time I had to replace a tire on my AWD Passat because of a tread separation, they (Les Schwab) told me I had to get all 4 new tires because they were worn more than 2/32" (NOT "down to 2/32"), and the different rolling diameter would damage the differentials.

Since the front and rear axles are not interconnected in any way on the M3, you can replace 1 pair. Put them on the back, because that is where most of the power (and regenerative braking) goes.

Yes that's exactly what I've heard, with such a minute difference in tread depth, it seems comical. By that same logic, everyone with RWD that have tires on the rear that are just slightly more worn than the front would ALL have issues.

I simply don't know much of anything about the mechanics and complexities of the M3, so I would have been scared either way to replace just one tire. I wasn't thinking of wear, I was just thinking if one of the tires blew, or had an unrepairable flat, would I have to match all the other tires.

 

[jjrandorin]

Yes that's exactly what I've heard, with such a minute difference in tread depth, it seems comical. By that same logic, everyone with RWD that have tires on the rear that are just slightly more worn than the front would ALL have issues.

I simply don't know much of anything about the mechanics and complexities of the M3, so I would have been scared either way to replace just one tire. I wasn't thinking of wear, I was just thinking if one of the tires blew, or had an unrepairable flat, would I have to match all the other tires.

If you have a flat tire in a model 3, and have 20 inch wheels, Tesla authorizes all wheel replacment tow trucks etc to put a 19 inch tire on there. In fact, I was told all roadside wheel replacement loaner tires from tesla for model 3s are 19 inch wheels, as their engineering stated that a 19inch wheel can be mounted on any model 3 with factory tires on it, no matter whether the car has 3 other 18s, 19s or 20s on it.

I asked for that in writing, and they sent it to me. They (tesla) state there is no issue with motors etc so any issue you would be worried about would be strictly traction related to wear. There is no issue with "the car" having only one wheel replaced, per tesla, specifically in writing to me, when I asked.

Unfortunately, me and tesla roadside are very wheel acquainted, as I have had to replace 4 tires and 3 rims total on this car already due to potholes, where I have never had to do that on other cars on same roads over 20 years of driving.

Anyway, on thread topic, TL ; DR, tesla says its fine, there is no AWD issue to worry about, unlike other cars, but I would still think about wear. No transfer case issues etc on this car.

 

[animorph]

The advice not to change just one tire has been around since long before traction control. The differential story made some sense, and handling and alignment makes some sense. Don't want it turning left differently than turning right.

I used to change just two tires (on the same axle) all the time. The main problem with that was different traction at the front or rear. Your normal understeering car could change to oversteer and the driver might not expect that or be able to react appropriately. For me, it was fun.