Don't forget, these tyres came out I think in the late1950s, and were also used as a " universal"Avon works hard at confusing you! The tyre names are often close to each other: SM = Speed Master or Safety Mileage?
I have the 400-18 Safety Mileage on the back of the 69 Interceptor. If you look at the profile it is rather square and although I no longer am
a foot rest dragger it does make you wonder about laying WAY over at the roundabouts. It also has the most rigid sidewalls on
any tyre I've ever used.