Star Rated Tyres
- Thread starter ronk
- Start date
Scottish Borders
Star rated tyres as B21 are specifically compounded for BMW, however there is usually a list of preferred tyres in your handbook. If you have a lease car there may be a restriction on what tyre you can fit, if not then you can choose.
The issue B21 described was a thing with the original X5, that had no slip allowance between differentials, it does not apply to the modern xdrive system that can distribute torque between axles via a multi plate clutch. That’s why you can have a staggered set up, as per the 435xd, where there’s a 1.5mm difference in diameter.
I think the transfer box issue is a one that’s been hyped up by every BMW forum, reality is that any system that couldn’t take a small difference in diameter wouldn’t be in production for long as it wouldn’t stand up in court. One of the prerequisites of European standards is that obvious and foreseeable problems have to be designed into a product during development and this most certainly qualifies.
The issue B21 described was a thing with the original X5, that had no slip allowance between differentials, it does not apply to the modern xdrive system that can distribute torque between axles via a multi plate clutch. That’s why you can have a staggered set up, as per the 435xd, where there’s a 1.5mm difference in diameter.
I think the transfer box issue is a one that’s been hyped up by every BMW forum, reality is that any system that couldn’t take a small difference in diameter wouldn’t be in production for long as it wouldn’t stand up in court. One of the prerequisites of European standards is that obvious and foreseeable problems have to be designed into a product during development and this most certainly qualifies.