If I were to build a wheel for tyres 40-50c, would it be an advantage to get 700c rims rather than 29er? Price difference?

Better choice of tubeless rims in 29er and many people use stans crest and old race gold with 700c cx tyres

Depends what’s you want light cheap disc non-disc

The ability to go wider or narrower at some point

Mavic touring rims a319 or some of the ryde ones seems good

Yup it’s about width. Wider better if you want to lower pressures.

Some 29er rims are mega tight with CX/road tyres – Crest are a case in point. If you are going 40mm+ then they should be okay.

Stans arch ex running 700×47 and 700×42 here no probs. 38s fit too but probably not ideal. No issues seating them, not particularly tight.

I’ve Maxxis Raze 35s on Arch EX no problem.

The newer mk3 stans rims seem to wider so check forst

They’d be a second set of wheels. I’d have one permanently with narrow tyres on and one with MTB tyres.

Disc only of course. But would like tubeless.

I run Pacenti SL25 29er rims with 40mm G-one tyres, gives a nice profile, easy tubeless setup and not too heavy.

And there we have it. Where do you draw the line? I use Pacenti cl25’s which were a 29er rim and then became a CX rim.
Matt above is calling sl25’s a 29er rim yet they have usually be sold as a road rim.
Ignore silly labels. They are all 622. And buy the width you fancy.

Only issue with mtb rims is tyre pressure. Off the top of my head mtb pressures are around 50 psi. Road rims take over 100 psi.

I guess that’s why they weigh more.

It always frustrates me that you can get lighter 29er rims than road disc wheels.

Road tubeless tyres have a different bead ( carbon ? ) witch helps with the higher pressure as well as the rim

It’s why you can’t bodge any road tyre as tubeless

Easton Arc are £40 at CRC just now. A little narrower than Arch EX and Crest.

Perhaps I should be “googling” for the answer, but I saw this thread and so will ask the question. I have 700c rims on my CX bike, if space is available (currently running 40c Nano’s with no problems) can I fit any 29er tyre on these rims? For clarification, they’re a Giant P-X2 which came with the bike. Not even sure if I’m able to convert to tubeless?

Road rims are heavier as they have to cope with higher stresses – inflate a tyre beyond 60psi on many MTB rims and it’ll probably tear the rim apart.

I’m not sure if you are replying to my questions, or just a general statement about mtb rims. My question is whether 29er tyres will fit 700c rims? Specifically Giant P-X2 rims?

The answer is it depends. Although I think the rims you are referring to are mtb rims even if giant stick them on a CX bike.

The width of the rim will dictate the maximum and minimum width of tyre you can use. So for example with an 19mm wide rim would be suitable for 28-44mm tyres, although you can normally exceed that a bit, at your own risk

Apparently the P-X2 is a 20mm wide rim. So will say any 45 mm folding 29er tyre fit? Probably revealing my complete lack of knowledge on the 29er / 700c thing, are they essentially the same diameter wrt compatibility? There, I’ve said it!

are they essentially the same diameter wrt compatibility? There, I’ve said it!

Yes

IME once you try a tyre beyond 2x internal width its down to the individual tyre and rim combo, particulary if the rim has a good bead hook. The rolling of the wheel can result in the tyre bead coming off, the inner tube failing catastrophically and possibly the tyre bead too – inflate with caution.