Roger,
Most of us in the UK run on Avon tyres - a 3.25 x 19" Speedmaster ribbed on the front, and a 3.50 x 19 Safety Mileage on the rear. Originally a 3.25 x 19 was fitted to both wheels but Avon no longer make the Safety Mileage in that size - so we have gone up one size.
Regards,
Eddie.