[hunter8793]

Is a 1% difference in tire diameter ok for the transfer case?

I was at the dealer and overheard a SA telling a lady the possible reasons why her transfer case needs to be replaced. He mentioned aftermarket tires having a softer sidewalk than BMW spec tires. I nearly LOL’d. Maybe he is right, if so, what a fragile system.

[ResIpsaLoquitur]

Originally Posted by hunter8793

Is a 1% difference in tire diameter ok for the transfer case?

I was at the dealer and overheard a SA telling a lady the possible reasons why her transfer case needs to be replaced. He mentioned aftermarket tires having a softer sidewalk than BMW spec tires. I nearly LOL’d. Maybe he is right, if so, what a fragile system.

This is a good question for pbonsalb. IIRC, the number he has mentioned for the variance is up to 1.4%. If that’s the case, you are probably good with 1%. It might be helpful for you to share the diameter of the tires you are considering vs. stock.

[hunter8793]

295/35r20 front and 305/35r20 rear continental extremecontact sport 2

Rear 28.41 inches
Front 28.1 inches

[ResIpsaLoquitur]

Originally Posted by hunter8793

295/35r20 front and 305/35r20 rear continental extremecontact sport 2

Rear 28.41 inches
Front 28.1 inches

Ah okay, you’re going wider than stock. I’m definitely not qualified to speak on this any more. I don’t know if there could be rubbing issues or the like. There are some knowledgeable folks on here who will certainly know this.

[hunter8793]

Another member had this wheel and size setup before and he even lowered it. Titan 7 wheels. He used a different brand of tires though.

I think he said the front wheels rubbed at full lock a little.

[Patton250]

Originally Posted by hunter8793

Another member had this wheel and size setup before and he even lowered it. Titan 7 wheels. He used a different brand of tires though.

I think he said the front wheels rubbed at full lock a little.

Do you think using these wheels he would have rubbing had he not lowered it also? I was thinking about getting these exact wheels with Michelin tires. I don’t need any headaches. I do not want to spend money to give myself a headache.

[pbonsalb]

The no risk sizes are 285/295 from all the research I have done. 295/305 may require fiddling with spacers depending on wheel offset, alignment, tire brands since the same size tires can vary from one brand/model to another, and ride height. You won’t find any definitive answers on 295/305 — the experiences vary and issues have been reported for both front and rear. For a lightly loaded car not lowered much, I think the problems will be the front, and mostly at significant turning angles that you may be able to avoid in routine driving if you are mindful.

305 effectively lengthen the rear drive ratio from 3.15 to 3.09. Better for fuel economy, worse for torque multiplication. I believe the front to rear difference increases more significantly over stock than the 285/295 difference, but it has been a while since I looked up all the sizes on a tire calculator. The front to rear difference is probably programmed into the traction control and ABS, so deviating would theoretically affect the reactions of those controls. Some also say deviating much more than stock can damage the AWD system. I have not read any reports of that actually happening on these cars, though.