and the 650b conversion begat the 650a conversion

The hard-to-find (but worth the effort) Schwalbe Marathon Plus in 650a (ERTRO 590-40) is a beaut. For those wanting to give to 26 x 1-3/8" shod Raleigh Sports Bikes greater rough-road capability, or for those wanting to effect a 700c conversion al a 650b, be sure to check it out.

Schwalbe even boast: "the SmartGuard® layer made from a flexible, special rubber offers particular resistance to shards of glass and flints. Even a thumbtack cannot penetrate this protective layer. The SmartGuard® belt does not increase rolling resistance."
I don't know about that yet, but I like Schwalbe, as who else offers a fat 650a tyre?