Soundtallica

My carbon disc braked CX bike that I use for gravel unfortunately has woeful tire clearance in the back. In the image below, you can see while it can clear a 38c tire (true width, it's listed as 42c), it's not enough to actually ride the bike. I'd say the max you can fit is a 36.

I want to put wider tires on my bike, so I've been toying with the idea of converting to 650b. My question is how does tire clearance for a 38c tire translate to a 650b wheel, and does anybody have experience with such a conversion? Will this amount of clearance allow me to clear at least a 650x42c tire (like the Cannondale Slate), since that's what I want to run? If not, how wide of a 650b tire can I use with this amount of clearance?

God bless disc brakes. The 650b conversion would not be possible on a rim braked bike without lots of extra headache.

shoota 

Brake out the digital calipers and start measuring.

justin1138

Ive been toying around with doing a 650b conversion on an older frame I have sitting around. This article has helped figure out what to measure and where. Good luck.

https://www.bikeman.com/bikeman-blogs...sion-guidlines

Tim_Iowa

Measure the width of the seat stays, chain stays, and fork 19 mm lower (closer to the axle) than the widest part of your current tire. That's where the widest part of a 650b tire will fit.
650b (584 mm) rims are 38 mm smaller in diameter than 700c (622 mm) rims, which equates to a 19 mm smaller radius.

Looking at your picture, the stays look pretty narrow for quite a ways. They're designed this way to improve heel clearance, but it does you no favor for tire clearance.

So, it looks like you wouldn't gain much in tire clearance with the smaller wheel diameter. You might be able to fit 650 x 42 mm tires, but maybe not.

Also, changing from 700 x 33 tires (what your bike is designed around) to 650 x 42 tires would lower the whole bike about 1 cm. Not a ton, and CX bikes usually have relatively high bottom brackets. So, probably not a big deal, except at CX races where you'd want the pedal clearance.

shoota 

Much better answer than mine, well said.

DarKris

Another note on BB Drop: I converted my bike with a 68mm BB Drop and 170mm cranks to 650Bx42 tires and occasionally had my foot hit the ground when pedaling. I was also running flat pedals so running clipless should yield better results. If you have a 60mm BB drop you should be fine.

Also since you didn't mention the fork I assume you have ample clearance there...