# different tread depth front vs rear



## TheBusDriver (Jan 23, 2018)

2018 540d xdrive 20" staggered set up

Rears: have 5/32nds tread left

Fronts: need to be replaced (out of alignment caused one tire to wear unevenly, and now road noise).

Question: have an opportunity to purchase 2 front tires (PZero, which is what's on the rear) with 8/32nds remaining.

Being an xdrive, will the difference in tread depth, (and thus tire circumference) cause any drive line damage?


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## Doug Huffman (Apr 25, 2015)

If excessive difference, yes. 1% circumference MAY be acceptable.


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## NytWolf (Mar 25, 2020)

The seriousness of this thread and the answer(s) boggles my mind. So you're telling me that BMW's xDrive system and possibly ABS system is so sensitive that it is affected by one (or two) of my tire(s) were off by a couple psi due to temperature difference? That's literally the same idea as the tires being off by 3/32 of an inch.

If you were changing tire sizes that would effectively increase/decrease the circumference of the tires, then yes, absolutely. But treadwear difference? A mere 3/32", at that. You're overthinking it.


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## Autoputzer (Mar 16, 2014)

Here's a blurb from TIS. It says the acceptable difference in tread depth for xDrives is 2mm (~2.5/32").
So, you'd be just out of the BMW spec at 3/32". Even with xDrive, the rears usually wear faster. That's to a large part because over 60% of the engine's torque goes to the rear wheels.

At 5/32", you've got most of the use out of your rear tires. Those used (?) 8/32" fronts and new rears (9/32" according to TireRack.com) would be just about ideal.

With staggered set-ups, sometimes the nominal rolling diameters (based on size, not accounting for tread depth). are different. That seems to be the case with yours; the rears having a nominal (theoretical) smaller rolling diameter of 0.25" (~1%) to start with. Although, that might be mitigated by more weight and lower air pressure on the front tires. Excluding that, you're putting a small but steady grind on the clutches of the xDrive case. Who knows if it's severe enough to cause a transfer case replacement (~$4k USD) in your future.

We bought an X3 xDrive for our eventual move north to a place with steep hills and snow. I specifically got a square set-up to have the same rolling diameters front and rear, and to be able to rotate the tires to maintain the same rolling diameters. I recently measured my tread depths. At 22k miles, the average in the front was 7.22/32" and the rears were 6.98/32". I'm due for a rotaton in about 2k miles. After the next rotation, the front and rear average tread depths sould be just about equal.


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## NytWolf (Mar 25, 2020)

So BMW wants you to buy new tires when there is a 1% difference in tire tread because their xDrive system is _that_ sensitive but want you to wait 10k miles for an oil change. So OP has 3/32" currently. When he buys new rear tires and keeps his used front tires, there will definitely be more than 1% difference in front-back tread depth, at which time he'll then be recommended to also buy front tires.

No wonder people think BMWs are unreliable and expensive to maintain.


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## Doug Huffman (Apr 25, 2015)

xDrive uses a clutched transfer case rather than a central differential. Different circumference front and rear will cause different relative speeds in the clutch members driving and driven. The transfer case clutch is a lubricated wet multi-plate clutch with variable engagement pressure, and it can tolerate considerable ‘wear’ - just not THAT much.

BMW does make 2WD vehicles.


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## Autoputzer (Mar 16, 2014)

NytWolf said:


> So BMW wants you to buy new tires when there is a 1% difference in tire tread because their xDrive system is _that_ sensitive but want you to wait 10k miles for an oil change. So OP has 3/32" currently. When he buys new rear tires and keeps his used front tires, there will definitely be more than 1% difference in front-back tread depth, at which time he'll then be recommended to also buy front tires.
> 
> No wonder people think BMWs are unreliable and expensive to maintain.


In the case of 20" wheels on xDrive G30's, the car rolls off the assembly line with a 1% difference, and it increases as the car is driven (as the rear tires wear faster). Nothing good comes form staggered tires and smart AWD. But, dealers love to sell tires, and really love to sell transfer cases. Also, people love the look of a staggered set-up.


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## billyjoe (Dec 13, 2020)

TheBusDriver said:


> 2018 540d xdrive 20" staggered set up
> 
> Rears: have 5/32nds tread left
> 
> ...


So, did you ever buy your new P Zero's?


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