Good day to you guys. I have this custom made steel gravel bike that currently has 700x35c tires on. I am planning on converting the wheelset to a 650b particularly the 650b WTB Horizon 47c. I have no problem with the fork since I know for a fact that it has a lot of clearance. But the frame builder told me that the max tire capacity of this frame is 700x38c but I figured that was just a conservative estimate since I already have successfully tried fitting a 700x41c Surly Knards in it but with very little room to spare.

The reason why I want to switch to 650b is because I find that the standover height of the bike is a little too tall for me and a mechanic told me that switching to 650b would reduce the standover height. None of my mates currently have a 650b wheels so fitting one at the moment is not doable.


Here are pictures of my seatstays and chainstays. The clearance for both stays is approximately
53mm.




Obviously, 53mm > 47mm but apparently, some tire measurements aren’t accurate at all. Was wondering if the WTBs is one of those tires. Am I able to fit 650bx47c in this bike? If no, what would be the thickest 650b tire that I can fit in this bike. Thank you all for your help. Much appreciated

With that setup you would have around 3mm of clearance on both sides of the tire if and only if whatever wheel you use sits directly in the middle of the chainstays. The reality is you can really only go through trial and error, if you can afford it. Long story short it could work but it looks like a 650b x 47 May be the max that could fit.