Having managed to fit a 26″ tube in my 29″ wheel on my 69er I’m sure it’ll be fine and I would just give it a go but now CRC do free returns I’d send them back and re order more carefully if they won’t work.

Unfortunately they are 28-35’s for the cx bike so the really obvious solution of going out and buying a 650 mountain bike to make use of them isn’t an option. 🙂