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700c to 650b conversion

Old 09-17-18, 08:27 AM
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700c to 650b conversion

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

Obviously, 53mm > 47mm but apparently, some tire measurements arenít 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

Last edited by manuelgabriel; 09-17-18 at 08:40 AM.
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Old 09-17-18, 01:59 PM
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You would have to do some calculations. - How to calculate Bicycle Wheel Size

700x42C has a diameter of 706mm. 650x1.9" has a diameter of 680.5mm. This puts a difference in radius of (706 - 680.5)/2. So I would put on the 700x42C tire and find the widest point that intercepts with your chainstays/seatstays. Then subtract the difference in radius and then measure again at that point. Hopefully there is at least 3mm of clearance assuming you have thru axles.
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Old 09-17-18, 02:10 PM
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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.
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Old 09-18-18, 05:51 AM
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Originally Posted by manuelgabriel View Post
Obviously, 53mm > 47mm but apparently, some tire measurements arenít 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
I've done the same conversion on one of my own bikes. The WTB Horizons are a rounded profile, and the 47 mm width won't occur at the very outer edge of the tire's diameter. Looking at one of my own bikes and measuring with a tape just now, the widest part of the tire appears to fall at around 330 mm from the center of the hub. And my experience with width is that the tires run close to their stated size, and maybe a touch under. I measured all four of my tires just now using a caliper, and their widths are 45 mm and 45 1/2 mm on the bike with narrower rims, and 46 mm and 46 1/2 mm on the bike with wider (28 mm internal) rims. I run low pressures, so it's possible I'd hit closer to 47 mm if I pumped in more air. Hope all this helps. Good luck in deciding. I'm pretty happy with my conversion. I was lucky when I started in that I had a 650b wheel on hand to test with.
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Old 09-18-18, 09:36 AM
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ISO standard is 6mm clearance on each side, so if it legally fits a 38mm it will have 50mm of clearance. I don't mind going down to 3mm clearance if there is no mud. I have some frames that flex a couple mm under high torque, and of course if you break a spoke or bend the rim the bike will be unrideable with tight clearance. You won't have this problem, but a tire with lugs is going to cause extra problems. So, it can probably be done with caveats...
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