Replacing just the rear tires ok?
 

I just replaced the rear tires on my 01 X5 after doing some research that suggested that it is ok to have slightly different sized tires (due to older tires being up front). This is one article I read:

http://www.4x4abc.com/4WD101/diffautoAWD_AWD.html

Excerpt from that article.

"There are some AWD vehicles where it does not matter what you do. Replace one tire, replace 2 - it does not matter. Those AWD vehicles are true AWD, in the sense that they are full time 4WD or permanent 4WD powering all 4 wheels with about equal force. Most Subaru (except Impreza), BMW X5, Audi, some Toyota, Mercedes, etc. are in that group of true AWD. These AWD vehicles have a differential between the two permanently powered drive shafts. They are the ones that will survive a replacement tire that is slightly larger or slightly smaller (like when you have to buy a used (larger) tire in Mexico because nothing else is available)."

But searching around this site has made me question that decision. Any input from you guys?

With the X5, you run the risk of damage to the transfer case for pre x-drive models (2000-2003). It has shown up as damaged splines.

With x-drive models (2004 onwards), the clutch plates in the transfer case allow for some discrepancy, but if it is too large you wear the clutch plates.

With both transfer cases, you can get nuisance DSC errors due to tire size discrepancies.

BMW has the same spec for maximum differences for both versions.

If the tires are the same size and brand/model front and rear, and one end is new while the other is up to half worn, you should be fine. I would put the new tires on the front, however. You will often have higher inflation pressure on the rear due to load carried, and that helps compensate for wear differences. Apart from that, you depend on the fronts for steering and braking.

I'd put the new tires up front too...

Thanks JCL and Sprocket! I will go ahead and move the tires to the front, even though I do not carry heavy loads in my X5 (I use my pickup for that). In addition to your reasons, the fact that the rears wear down much quicker is yet another reason to put the old ones on the rear.

I did my best to measure the total circumference and I got about ½ inch difference. That still sound ok?

I did the tires 2 weeks ago, and took it on a 1000 mile road trip and I received no DSC errors, but a damaged transfer case would be scary!

How ? The planetary gear in the transfer box acts exactly like an open differential, there's no locking mechanism that will allow transmission wind up.

Due to my staggered set-up, I've done this twice (most recently about 15,000 miles ago) and have had no problems. I wouldn't waste time worrying about it.

A statement like that needs some context. What are your tire sizes?

I'm running the stock 4.4 sport package 19" staggered set-up.

I've changed the fronts tires only and the rear tires only, at different times, due to differences in treadwear b/t the front and rear.

Never had a problem.

Done exactly this with my 3.0i (06) and havent had any problems either. In fact when I bought my x5 there was a problem with one of the rear tyres and bmw changed the two rears and not the fronts. Ive since changed the fronts and never had a problem.

If you are sticking to the stock sizes then I'm not surprised you didn't have any problems. It's when you go +1 or +2 on the wheel sizes or go wider than stock that you can get into trouble since the correct tire diameters may not be available.