I have a Pacific Reach folder that uses the 20 X 1 3/8" tyres. The ones I have at the moment are almost shiny smooth and I would like to be able to use it safely on the odd cinder track, canal towpath sort of thing. I'm sure it is the 451 size but don't know anything other than the old "Raleigh White wall shpper" stuff. Any good guides to a relatively good quality tyre with a bit of tread that wouldn't be like a Pig on roller skates on a Muddy track?