Well they are Avons.....but I am guessing you knew that.
They look like roadriders to me, which Avon sells specifically for the R100 in non metric sizes (3.25-19 front and 4.00-18 rear).
Roadrider | Avon Tyres
They look like roadriders to me, which Avon sells specifically for the R100 in non metric sizes (3.25-19 front and 4.00-18 rear).
Roadrider | Avon Tyres