maybe it was because Avon makes that 19" sidecar tire which has a flat profile versus the rounded profile of a motorcycle front tire. But a size that could fit a radial tire would be much improved (IMHO. There are shops that will re-lace a wheel, and so that is one option. However, lacing a wheel is not in my skill set
So what you are saying is that the wheels need to be relaxed for radial tires? Different spoke pattern?
