A lot of the blame seems to be attributed to the run-flat tyres standard on the Z4 3.0, but the only way to find out for sure is to swop them for conventional rubber. That's why we've just fitted a set of Vredestein Ultracs.

Talking to Vredestein UK MD Bert Stellinga about run-flats in general is illuminating. He believes they aren't yet ready for the market as the ultra-stiff sidewalls of a run-flat are ride-wreckers. In fact, on the Z4 the sidewalls are so rigid that without the on-board tyre pressure monitor to warn you, it'd be easy to drive around without any air in the tyres. And if you do puncture a run-flat it can't be repaired, you have to junk it - and as a 255/35 R18 run-flat for the rear of the Z4 costs ΂£200 compared with ΂£137 for a conventional Vredestein Ultrac, that's quite a consideration.

The Bridgestone run-flats were wrapped so tightly around the Z4's rims it took two tyre fitters a whole day to prise them off. Once I've had a chance to drive around on the new tyres I'll let you how they've affected the Z4; whatever the outcome, I doubt we'll be fitting run-flats again.