Can't say I notice a problem with sidewall flex in the rear tyre Martyn, the back end slides around quite easily and also squirms with wheelspin off the start line, which is great fun but not the fastest for acceleration. My main reason is for the lower gearing which might gain me quicker acceleration (if I control the wheelspin) and allow me to make far more use of third gear in hillclimbs and sprints.

I ran out of revs in second gear at Loton Park, but found no gain in changing to third to then very quickly brake and downshift back to second at Triangle bend. Lower gearing might not reduce my times, but if I don't try I wont find out....