Yes...ALL X5s are AWD.

Unfortunately, no one knows what the long term ill effect would be running the 0.45" differential. I supposed it's equivalent to running an almost bald set of fronts with a brand new rears with full thread thickness.

Frankly, I'm not sure where your tire guy got those tire sizes from. The OEM sizes would work on all X5s, whether 3.0i, 4.4i, 4.6iS, or 4.8iS.

FYI...the differences in side profiles between the 295/40-20 and 315/35-20 is negligible as my above calculation showed. Why? 40% of 295mm is your side profile (295/40-20) versus 35% of 315mm side profile (315/35-20).

Here is the fix (DKL, I think you will agree - I hope so anyway and I am very eager for your reply) :

We replaced the front tires this morning, with 265/50/20 and kept the rears with 295/45/20. All the tires fit the rims well, and all tires have wheel well clearance.

The overall diameter on both sizes are now identical at 30.6" and the revs per mile are also identical at 679. I could not figure out your formula for determining the rolling diameter, but do know according to the revs per mile and the overall diameter they will mathematically get the same rolling diameter, for each size.

Here is the specs for the Yokohama Parada Spec-X:
http://www.yokohamatire.com/tires/sp...ARADA%20SPEC-X

I hope my "crisis" is avoided and I can get on enjoying the X5 ride...:D

It looks like that combo will work. My theoretical calculations are:
265/50/20=30.43"
295/45/20=30.45"
Tires from different manufacturers will vary slightly even for the same specified size (due to different thread depth, etc...). That's why you don't want mixed tires from front to back or side to side on AWD.

Your new tires are still a bit taller than the factory 17s (235/65/17=29.03"), so it will throw off your speedo a bit (you'll be going slightly faster than what's indicated). But that's no biggy since the factory speedo is a bit optimistic to begin with anyway.

I just got lazy and copied this from the training book for you, this is for post facelift X5's with xDrive only, itis hard parts failure on pre-xDrive X5's.. enjoy!

http://i140.photobucket.com/albums/r.../xdrive015.jpg

W, Thanks for the excellent info! I learned something new about the X everyday. Even though it's designed into XDrive to allow for slight tire circumference deviation, prolonged transfer case clutch slippage cannot be a good thing on the TCase when the differential increases, right?

Correct. Just think of it in terms of clutch wear, but the clutch packs are loaded by electric actuation and connect your front wheels.

I had excellent results using 295/40-20s F&R on staggered 20" wheels. I had no circumference issues. See the FAQ page for more info on my experience and that of others who have done this mod.

Wild-one, you're fortunate to have such a friend who would swap you out after mounting and installation of the first set of tires! I'm glad it worked out.

If you used the same size tires front and rear, then why in the hell did you buy staggered wheels?!? That kinda defeated the purpose of having the wider wheels in the back!

Yeah, I did get lucky. He said it was no big deal and did not charge me anything at all, to do the swap... thanks for the replies everyone - this was definately a good learning experience.

I am feeling a very slight "shimmy" now while driving at highway speeds. Is this suspension parts wearing because of the larger wheels/tires?