Well guys, I feel like a bit of a loser here because I've abandoned my R24 project. The choice of good HP narrow tyres for the 507 size I've got is very limited if not non-existant. Next time I''ll check these odd sizes better before I buy.....Anyone need a set of Velocity 24" MTB rims?
In the place of the R24 project I'm building up a R20 consisting of 451 Velocity rims with a Sachs 3x7 rear hub and a Shimano LX Deore front hub, not the same as a R24 but still fun to build.