I kept the same circumference (18 and 21 inch), but had to go for wider than stock rims (2.15 and 2.5) as the Excel rims smaller than 2.15 don't come with the safety bead for tubeless tyres.

Problems arose when, during fitting, it was discovered the spacers on the front wheel were the wrong dimensions to take the spindle. So, rather than spend weeks of back and forth with the suppliers, my mechanic (John) fabricated replacements after an attempt to bore out the spacers left them dangerously thin. This meant new, non standard wheel bearings for the front (Inner 17mm x Outer 42mm x Width 13mm). After putting it all back together, the ABS warning light came on, so the sensor had to be shimmed out. Not ideal.....but I took it for a test ride from London around the NC500 and back. All good.

I am very happy with them and would do the same again in a heartbeat.
Cheers.

Thanks for your reply...greatly appreciated.

I'm communicating second-hand with Hahn (through a local dealer) and on my initial enquiry they reported to me that Hahn talked about a 1.85x21 and a 2.50x18. I then bought to the attention of the dealer the Hahn website info you mention above. I've yet to hear back and suspect it may be a mis-communication. Also, no price details yet. I'm prepared for expensive but, of course, it could prove prohibitive.

I've spoken to a few wheel builders in Australia, buy yet to find anybody who regards tubeless conversion as a mystery.

Thanks for your reply...greatly appreciated.

Forgive my ignorance, but does that mean that your problems with the front wheel stemmed from the supplied hub being different from the original? New spacers and bearings and shimming the ABS ring sounds a bit beyond my scope.
My initial thought was to go for rear wheel only, believing that would reduce my chances of of a (tube) puncture by a factor of more than 50% and necessitating an easier repair in the event.
I'll continue my investigation and report back.

Yes, the supplied hub was not the same as stock. I don't know if that was a mistake on Hahn's part or just a standard size they use. Fortunately, I have a very good mechanic nearby who sorted out the fitting. I could have gone back to Hahn, but I didn't want to waste time going back and forth. As I say, very happy with the wheels.

Thanks again, I do appreciate your help.

I’d say it’s not a huge issue unless you’re really pushing the bike off-road. Slightly wider rim might change tire profile a bit, but on a CRF250 Rally, I doubt it'll mess with handling too much. Definitely not overthinking — better to check now than regret later.

If you're worried about the compatibility of 3rd party hubs, then just get your existing wheels re-rimmed with the the tubeless rims, or buy a set of stock CRF hubs and get those built as new wheels with the rims you need.

OEM CRF300 hubs are not expensive (and a lot cheaper than typical 3rd party billet hubs), and obviously everything will work with the stock hardware too of course.

Depending on which company you get to lace your nubs and new rims together (ie. usually based on your location), their is every chance they can install/seal them for tubeless too - but DIY sealing is not scary thing to do, particularly if you're doing it to brand new rims.

Jx