Hi guys, I’ve just bought a new Ridley from Merlin cycles and it’s my first ever cx bike. It is a lowly model and comes with fulcrum dB cx wheels that seem to have a 20.5 mm external rim width. Does anyone know the widest tyre I can put on that rim? Frame clearance doesn’t seem to be an issue. Thanks. 

I have some with 40mmwtb nanos on (using tubes) . Nice wheels once you change the extremely crappy bearings out of them, the front on mine siezed fairly quickly

I’d guess the frame will struggle to clear anything more that 35-38 ish

and I’d guess your wheels will be fine

I used old mavic open pro (quite narrow internals) with 35mm tyres for years (did the 3 peaks on them too)

Thanks guys, my frame has lots of clearance with the standard fit 32 tyres so I don’t see a problem with 40 as long as my wheels can take it.

I use Stans Alpha’s with 40c tyres no issue and they’re pretty narrow