I was experimenting in getting 650b wheels on a 700c cross bike, and its generally went well- but clearance on the chainstays with 42mm tyres is tighter than I’d like. It will be fine in good conditions, but with clag added- maybe not.

Has anyone seen any decent 650b 40mm tyres for sale anywhere?

Think you might struggle a bit there. Smallest decent tyre I can think of is a resolute at 42mm. I tried them but it was the worst of both worlds, smaller wheel and small tyre, resulting in an overall wheel circumference that meant it was bloody hard work trying to keep up with mates on 700c.

Thanks TW. Indeed, and its 42mm Resolutes that I have on the bike right now :/ ah well…..

Out of interest whats your 700c clearance? And why did you want to try 650b?

No probs, thanks for asking.

Its a Raleigh CX frame, the “Team” one, so fairly racey. It takes a 35mm 700c tyre with not bad clearance, but thats it. Its really designed to go fast on a CX course, something that rarely happens with me, and with 35mm being the UCI mandated max width then the frame is obviously designed with this in mind.

I’ve been using it pretty much solely as a gravel bike for well over a year. I’ve got an enjoyable out and back local loop of 36 miles or so with about 7 miles of B road, then 11 of windfarm tracks. Its kept me fittish for a while, I get an uninterrupted couple of hours with no hassle with a decent climb thrown in. All good.

However, I had a loan of a Vitus gravel bike a few months ago with 42mm tyres and was impressed at the difference. It was definitely faster and more comfortable, and completely puncture free. So I imagined that bigger tyres= way forward, but the chainstay clearance was the kicker- so 650b & 42mm tyres seemed the way to go about it.

What I clearly need is a different frame :/