You still don't get it. Good luck with everything buddy. :thumbup:

RPH74, you made the right decision by replacing all four, good piece of mind having good rubber all around. I was in the same situation a few years ago and just replaced the rears which ended up being fine for my situation - I have 117K miles now and no damage to the tranny or transfer case as a result. This past winter the fronts were getting a bit thin and were noticeable in the bad winter we had in the Northeast, the start/stops in the snow were just not very good. This spring, I replaced all four just to get back to a good rubber baseline even though the rears were just fine. I kinda felt bad about tossing out two good tires, but my wife drives our X5 alot with the kids, so I felt a few hundred $$$'s is worth it. Keep us posted on your ride!
:thumbup:

@JCL, your point regarding the x-drive models (2004 onwards) being afflicted by using differing tire size, mine (a nov 2004 built 3.0d) is not a xDrive no mention of this anywhere on 'packet' or manual, had a case over the last few years where left side tires were substantially more worn over the entire circufmerence of the tires than the right so rotated them (they werent directional), never had a dsc error popup, just be good to know if there is any hard fast empirical data for the e53 where owners have used mismatched tires (as you say most had 17" stock rear andt front) and has lead to transfer case failure and the like.. Reading online today have seen that some of the much newer bmws are more susceptible, but for our X5s is this something as I mentioned in another post that would just go kaput on the highway or would we get a warning?

Why make you say your 3.0d is NOT xDrive? It almost certainly is.

You have a "facelift" (LCI) E53 X5 and they all have xDrive. The xDrive driveline was fitted to all LCI E53 X5 produced, starting in late 2003.

And so yes, tyres are important. You need to keep the rolling circumference of all tyres with a couple of percent of each other or you risk wearing out the clutch packs in the transfer case.

Documented evidence of this happening...? Dunno. :dunno: But I don't want to risk it... ;)

So i found this:

That works out to just about 4/32" difference in tread depth allowed front to back. I don't believe the 3% of OE for overall size as long as they fit and are all the SAME size or within 1% rolling circumference.

That is for x-drive. i think the pre LCI can have up to 3% difference front to back axle.

Spoke to my mechanic and he confirmed seeing it (drivetrain issue) on X3s with mismatched tires, so gonna go get em changed today

Im late to the party here but here is my situation. A coworker gave me two tires for the front, Pirelli P Zero Nero 275/40R20. They are slightly used and were taken off a different car that got racing tires. So I looked up that same size tire for the back but found that Pirelli does not make any in my size. I ended up getting two Pirelli Cinturato P7 315/35R20 for the rear, although I haven't installed them yet. My concern after reading this thread is that my tires are 2 slightly used in the front and two new in the rear. Also the tire models are different. I thought it would be fine since my E53 has a staggered setup from factory and the tire sizes are already different. Also the tires are all made by the same manufacturer, although have different thread patterns being that they are different models. Should I just buy two new tires for the front and keep those other ones as spares or will I be fine with what I planned to do? I also really want to use Michellin but I am kinda stuck with the Pirellis since that is what my coworker gave me and I don't want to be rude if I don't use them. If I get new Pirellis in the front, maybe he won't notice that they are not the same ones he gave me.

Sorry for rambling, also forgot to mention I have an 06 E53 with the 4.8is engine.
Thanks

Since you say they came from a car, replaced with racing tires, I'll suggest to first check on the load rating of the tire. Not sure about your '06 4.8is, but my '01 3.0i specifies 103V in the front and 107V in the rear. The V speed rating means any of V W Y Z will work. And 103 or higher will work in the front, 107 or higher in the rear.

Ok, any clue where I can find the load rating that I’m supposed to have? Is it in the manual?

Should be. It might also be on the plate inside your driver's door jamb, along with the recommended inflation pressures. And of course the tires will have it on the sidewall.