Mixing tyre brands
 

My X5 came with 20 inch M sport rims and Dunlop sport maxx tyres but I've just replaced the fronts with bridestone dueller sport hp tyres. The fronts have 8 mm of tread depth and the rears 3mm at the centre, 4mm at the sides. Is there going to be a problem with transmission wind up given the slightly different rolling diameters? Many thanks in advance for any advice offered.

WHAT ARE THE "Revolutions per mile" for the front tires and the rear tires, AS PUBLISHED ON THE TIRERACK WEBSITE????

What is the specific tire size?

While the tread depth difference is usually negligible, one mfgs tire may be quite different in rolling diameter from anothers, even for the same nominal size.

My car runs 275/40 20 in front and 315/35 20 at the rear. Just looked at the tirerack website. Dunlops run 721 revs/mile and bridgestone 726 revs/mile. Is the difference enough to cause a problem?

There you go. That is the definitive way to assess tire matching.

In your sizes, the sport max runs 721 for both sizes- a perfect match.

When the revs per mile are off, the difference in rotations must be 'absorbed' or 'dissipated' by the differential. A difference of 5 revs per mile, or one rev per 10 seconds or so, is fine.

Now to further split hairs, the bridgestone runs a tad smaller than the dunny (that is why the revs per mile is larger, it is minutely smaller) Hence since you actually have more tread on the bridgestones, the tread thickness variation is actually balancing out the difference.

Oh, and when the tire store tells you scary stories about "Oh, these AWD cars can be damaged if you don't replace them all", just laugh.

Thank you. I did figure if the revs/mile difference was large enough the traction control/stability management system could get confused but not at 5 revs/mile. Forgot about the tirerack website when I was trying to get more info about the tyres as I'm based in the UK and don't order tyres from them but they are a wealth of information.