What’s causing front-end shimmy?

Q. I am getting a slight front end shimmy at higher speed on my Honda CBR600F. The bike is fitted with Pirelli Diablo Rosso Corsas and I’ve done 1000 miles on them during which time they have been brilliant; very stable and with tons of grip. I did do a track day the other day.
Gareth Vaughan, email

A. If it had been in the first few miles during the ‘running-in’ process we’d say it could have been because the tyre hadn’t seated itself properly on the rim. Sometimes front end movement can be partly due to lifting the front of the bike at higher speeds.

In this case though, I think it’s your tyre pressures. Racetrack pressures can be up to 10psi lower than the road, and even if the front tyre is up to pressure, a reduction in the rear can set up a resonance through the chassis that you feel through the bars. Lower tyre pressures can also reduce the life of the tyre by 20%.