Tyre size (?) problems…..

[sevenfourate]

Just gone to mock up my new wheels and tyres on my latest BMX build - to find this happens:

Wheel rims are wide (40mm). That’s wide for anything but an extremely modern BMX made for ultra-wide rubber…….

And with these 2.25” United tyres - the total width when blown up is right on 60mm ! 😳

However - if I put a rim in central: but without a tyre on…..I have loads of room:

And looks like I have right on or just under my 60mm tyre width at the point the tyre is in the narrowest part of the frame:

So: As long as wheel / tyre run true I SHOULD be ok with a 2.0 / 2” / 51mm tyre ? But how does having a wide rim effect that ?

Am I better buying a pair of 1.75” tyres to be sure. And knowing they might come up fatter 🤷‍♂️ because of the wide rim ?

Desperate to order / get this thing built. All experience appreciated 🙏

 

[N0bodyOfTheGoat]

On a MTB, a typical good internal rim width for a 2.35" tyre would be ~25-30mm iirc. Narrower rims lower the real world tyre width and makes the tyre profile more tear shaped... Which can then lower their contact patch grip when inflated harder.

40mm IRW for a 2.25" sounds crazy, no wonder the tyre is measuring wide!😱

I recently had a 50mm Schwalbe Century on the rear of my Voodoo Marasa, iirc the replacement wheel was ~22mm IRW and the tyre only measured 46mm (some of that could be the tyre, manufacturers often give optimistically high width, which then makes them weight competitive with an accurate width tyre). If I put the Century on my Bolt's ~25mm IRW wheels, I'd expect it to be wider and become very borderline in clearance as the Bolt officially accepts 47mm.

 

[sevenfourate]

On a MTB, a typical good internal rim width for a 2.35" tyre would be ~25-30mm iirc. Narrower rims lower the real world tyre width and makes the tyre profile more tear shaped... Which can then lower their contact patch grip when inflated harder.

40mm IRW for a 2.25" sounds crazy, no wonder the tyre is measuring wide!😱

I recently had a 50mm Schwalbe Century on the rear of my Voodoo Marasa, iirc the replacement wheel was ~22mm IRW and the tyre only measured 46mm (some of that could be the tyre, manufacturers often give optimistically high width, which then makes them weight competitive with an accurate width tyre). If I put the Century on my Bolt's ~25mm IRW wheels, I'd expect it to be wider and become very borderline in clearance as the Bolt officially accepts 47mm.

Sounds like even 2” might get close to the frame with some tyre run-out / wobble - and the wide rims making the tyres come up large. Looks like I need to try some 1.75” in the first instance…….

Thanks for your thoughts 🤷‍♂🙏

 

[sevenfourate]

On a MTB, a typical good internal rim width for a 2.35" tyre would be ~25-30mm iirc. Narrower rims lower the real world tyre width and makes the tyre profile more tear shaped... Which can then lower their contact patch grip when inflated harder.

40mm IRW for a 2.25" sounds crazy, no wonder the tyre is measuring wide!😱

I recently had a 50mm Schwalbe Century on the rear of my Voodoo Marasa, iirc the replacement wheel was ~22mm IRW and the tyre only measured 46mm (some of that could be the tyre, manufacturers often give optimistically high width, which then makes them weight competitive with an accurate width tyre). If I put the Century on my Bolt's ~25mm IRW wheels, I'd expect it to be wider and become very borderline in clearance as the Bolt officially accepts 47mm.

It’s 40mm OD on the rims I have. **Just measured and it’s 33-34mm IRW.

Either way: I’ve now ordered some 1.75” / 44.5mm tyres. I figure if these grow a little on the wide rims - I’ll still have a little clearance. If I got 51mm / 2” tyres and those grew AND then had a little run-out / lateral wobble - I’d be back in the World of rubbing again………

Cheers for your thoughts.