Originally Posted by TaMbALoLoNg

I agree pretty much 100%, but the difference between 275/40 and 295/40 is only 8mm, which is practically nothing and you can pretty much balance it out if you have less PSI on your rear tires. It shouldn't put significant amt of stress on the drivetrain worth worrying about.

Originally Posted by weasel56

The wheel sare all tied together through the drivetrain, all pushed at equal speeds by the engine. The bigger diameter of a tire, the further it rolls per one rotation. If one set of tires are bigger than the other, the bigger set will push the smaller set and the smaller set will drag the bigger set... putting LOTS of stress on the drivetrain.

The tire sizes work probably different than you think. The 1st # is the tread width in millimeters, the 2nd # is the aspect ratio and works off of a percentage of the treadwidth... so a 275/40 is different height from a 295/40 and so on. The 275/40 and 315/35 are at the same rolling diameter which is why they are the best tire size option.

If you go on a site like tirerack.com and click "specs" when looking at a tire, it will give you the overall diameter and revs per mile for each tire size. Here's some to look at.

Dunlop did their homework to make tires the same size: http://www.tirerack.com/tires/Spec.j...e1=yes&place=0

Yet look at the different #s on the yokos:http://www.tirerack.com/tires/Spec.j...e1=yes&place=0

Originally Posted by gatchalian

is it a problem if you use 295 40 20 on all corners

Originally Posted by TaMbALoLoNg

Will a 315/35/20 tire fit in a 20x9.5 wheel, what will be the con?

Originally Posted by X5-limo

I assume that there's some equation that the tire techs use when they make their tire combo recommendations(?)

Originally Posted by rayxi

It's not rocket science - just simple geometry. Check here. There are other sites with similar pages on the Web.

Originally Posted by weasel56

The difference between 275/40 and 295/40 equals out to 18 full rotations per mile!!! I have personally seen and had to fix the problems created by this, namely... transfer case. In 2000 - 2003 X5s it usually strips the splines at the front output shaft of the case costing you a front driveshaft and a transfer case. In 2004 - 2006 X5s it causes substantial wear to the clutches in the case where it transfers torque split to the front wheels, causing once again the transfer case to need replacement.

It would be like having different gear ratios front and rear of your 4 wheel drive... you just don't do that.

Originally Posted by TaMbALoLoNg

Have you had any drivetrain problems with your set up? (295/40)

Originally Posted by TaMbALoLoNg

Makes perfect sense. The above is my current set up but I'm going to replace my rears to match my 275 fronts, I certaintly dont want future transfercase problems. So far I dont notice any problems right now and my X runs great. So i guess its either 275 or 295 all around. What do you think? This have been a very informative thread..great job guys:thumbup: