E83 X3 transfer case issue and tyres

[e460rob]

Can someone clear something up for me, I'm having the classic signs of problems with transfer box from mismatched tyres. It makes a clunk when driving in slow traffic or mostly in second gear (auto). I have Dunlops on the front 235/50/18 and Avon 255/45/18, all mostly worn to about 4mm depth. I'm lead to believe problems occur due to rolling radius differences. Am I right in saying if I went for a 50 profile back and front I would no longer have a problem? Do the tyres have to be star rated or will the problem dissapear along as the tyres are same brand, tread depth, tyre pattern etc? Only reason I ask is I really want to sort this before the box chucks itself out but I really can't run to £110+ per corner at the moment. I've always used avon or nankang! Any help much appreciated. Many thanks

[rassi]

The E83 X3 is known for a troublesome transfer case when using mismatched/not evenly worn tyres which leads to a significant difference in rolling radius, even more so when it has the staggered setup like yours.

Some have cured it with 4 new tyres of the same brand and model, others by fitting new tyres that are * marked.

The jury is probably out in which one is necessary. Your idea of fitting non staggered tyres is not a bad one, as it is the easiest way of ensuring equal rolling radius, but you will find that the rear wheels are wider, so ideally would want the wider factory sized tyre too. However, it should technically be possible to do so, but you will need 4 new tyres in any case.

[Origin Unknown]

OP, did new tyres solve the transfer case issues?

I have an e70 X5 with the same symptoms. Rears are due for replacement (30k out of them isn't bad) and I'm wondering if I should replace the fronts at the same time.

[e460rob]

I haven't had the time to do anything about the tyres yet, but I am very tempted to go for non star rated just as long as they are same brand, correct size and same tread