Why can't you get run-flat tyres for motorcycles?
Q. My BMW car is fitted with run-flat tyres which I appreciate as I got a puncture the other day about 60 miles from home. I was able to continue back home at 40 to 50mph, although I couldn't get it repaired.
Seeing as a puncture on a bike could be more dangerous, why haven't run flat tyres made it on to motorcycles yet?
James Cooper, email
A. The first run flat car tyres appeared 10 years ago and they achieved their aims by making the sidewalls double or treble the thickness of standard rubber. That makes the tyres much stiffer and those first tyres felt 'dead' with little feedback.
They are also a lot heavier than standard rubber, not so much of an issue on a two tonne car where the ratio of unsprung to sprung weight is quite low, but on a bike any increase in unsprung weight adversely affects the handling.
Bike tyres also have some flex designed into them as the demands on their performance change from upright to 45-degree lean angles.
It's taken a decade for run flat car tyres to have acceptable performance, so run flat bike rubber isn't going to appear any time soon.