Should all 4 tires be exchanged at the same time in order not to destroy the transfer
 

Hi, I thought about buying 2 new winter tires but on some 4 wheeler it's important to change all 4 at the same time so it does not hurt the transfer, this also applies to xdrive or it's okay to simply change 2 tires in front

X5 E53 2004 mod 3L diesel

Yes - it matters very much on xDrive.

It depends on the wear on the remaining two tyres and the overall rolling circumference.

Ideally, to ensure you don't wear out your transfer case, you need the rolling circumference of all four wheels to be with about 1.5% (or less) of each other.

Many tyres will change by more than 1.5% over the life time of the tyre, due to tread wear. Depends on the tread depth when new etc.

You can calculate the variation using a calculator like this one.

https://www.omnicalculator.com/math/circumference

In most cases, you should be OK just replacing two tyres (same size and spec etc.) , as long as the other two are very similar in rolling circumference. YMMV... literally....

Literally…awesome


Sent from my iPhone using Tapatalk Pro

Should all 4 tires be exchanged at the same time in order not to destroy the transfer
 

I just looked up for somebody this situation and wo xdrive it's apparently ok to have 3% difference as the manual spec allows 285/45-19 and 255/55-19 on as well as 255/55-18 square.

Look in your manual and see what it has for stagger options and find what BMW actually says is ok for front to back difference and use the tire calculator.

Should all 4 tires be exchanged at the same time in order not to destroy the transfer
 

I actually would not recommend different traction on front v back axle. The traction control and stability control will assume traction of same tires and it could put you in a ditch if the math is thrown off from different tires front v back. That said BMW says to only put chains on the back when necessary so go figure. Read what the manual says.


Sent from my iPhone using Tapatalk Pro

Have placed different tire brands and old vs new on axles for over 17 years on 7 different AWD vehicles. Not one issue, ever. I did run a larger than recommended rear setup (5% difference) on my 4.4 years back and after 10 miles the entire vehicle would shake violently and I had to drive very slow back home, swapped them out for tires within spec, and all was fine for another 30k miles (sold at 196k). It will not unknowingly destroy your vehicle, you will know. I also ran my 4.4 off road for over 25k of those miles, never any traction issues, or other annomalies.

Not a single AWD vehicle I have owned has worn front/rear tires evenly. So, when the rears are worn, I will buy new rears. When the fronts are worn, I will buy new fronts. Generally, my preference is to buy all 4 if they are available at the same time, not always the case, and I never allow tires get under 40% tread, I buy new tires. I also drive more aggressively than average.

Funny that you said not one issue ever then the next sentence describes an issue you had. Helpful feedback though interesting it took 10 miles to piss off the computer. Might have been able to just disable DSC.

They were size up tires, not recommended tire sizes, I should have stated that when I typed larger. Had nothing to do with the computer, it was the transfer case. It was also entertaining.......:)

I'm guessing your 4.4 was pre-facelift? The NV125 transfer case is a fixed power divider and would behave as you described ("wind up") if running with mis-matched axle speeds.

The later facelift cars, fitted with the ATC500 transfer case, would possibly behave rather differently. The clutch packs in the ATC500, which provide the variable power dividing ratio (xDrive), could just simply slip but could also suffer accelerated wear due to this slippage. Or worse... :dunno:

Post. It was very apparent the clutch packs were trying their best.

Good to know the ATC500 can take some abuse and still be good to go for many more miles!! :thumbup:

Difference of tire traction capability will not fool the computer. It senses loss of traction and compensates accordingly.

The wear difference side to side from a new tire to a tire that has a few miles left on it won't cause any problem.

On a square tire setup- If you change tire height of one end all four tires should be changed to match.

On a staggered setup- If you change tire height of one end you should also change the tires to the same height on the other end.

The factory handling characteristics include choice of tire size. When you change tire height or tread width it changes handling. If you change tire height it also changes final drive ratio. Taller tire will reduce acceleration and increase top end. Shorter tires will improve acceleration and reduce top speed. Shorter tires can reduce mileage.

I have no interest in taller tires as they also raise the center of gravity and stock tire size already allows a top speed I never should be going on the street.