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700c to 650b Conversion Questions

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700c to 650b Conversion Questions

Old 03-25-21, 01:02 PM
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700c to 650b Conversion Questions

Hey everyone -

So I got into gravel riding last year and I love it. Since I bought my bike, I've put way more miles on it than my road bike by about a 3-1 ratio. Unfortunately, I didn't really know what to look for when buying a gravel-specific frame, and so the bike I ended up with (Scott Speedster Gravel 30) has geometry that makes toe-overlap a bit of an issue. On most trails this is not a problem, but I like to ride a lot of singletrack with switchbacks and on any sort of tight switchback, I ended up hitting my tire with my foot which is scary/dangerous. I've learned to deal with it to a certain extent, but it still bugs me and prevents me from taking really tight turns.

Part of me wants to just get a new bike without this issue, but that's another big expense that I can't really justify right now. Before making a purchase like that, I'd like to try and solve the issue with the current bike.

I've found a set of 650B/27.5 wheels locally that would work with my bike (correct thru-axle specs and all) for a fair price (about $200 for DT Swiss rims + hubs) but I would need some tires for the wheels.

My questions are as follows:
1. Is this conversion likely to solve my issue? I tried moving my cleats forward on my shoes but that puts me in a weird riding position and hurts my knees - I have them as far forward as possible while still being comfortable. The toe-overlap is a matter of probably a 1 cm or 2 at most.
2. What size tires would be recommended? I'm currently running 700x37 WTB Riddlers which basically max out my frame clearance. The bike came with 700x35 Schwalbe G-Ones. I'd obviously like to stay as wide as possible, but eliminate the toe-overlap issue.
3. Is there any reason I would not like 650b tires even if it does solve my issue? I tend to mostly ride dirt on my gravel bike, but obviously I do ride tarmac to the trails as well. I know 650b will probably be slower on tarmac, but I'm ok with that if it solves the toe issue.

Thanks everyone!
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Old 03-25-21, 01:26 PM
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The 650b wheels will definitely help with the toe overlap, unless you put on much larger tires.

The wheels will effectively decrease trail, so the bike will likely be more nimble/twitchy.

Personally, I would put as wide a tire on there as fits the frame (while paying attention to the toe overlap issue).

Rene Herse tires:
https://www.renehersecycles.com/prod...ts/tires/650b/

I would go with Pumpkin Ridge to begin with. The beauty of these tires is very low rolling resistance, so they will be ok on road too. (Tires are much more likely to slow you down than wheel size).
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Old 03-25-21, 01:27 PM
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From the master;
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Old 03-25-21, 01:28 PM
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When switching over to 650b, I would hope you could put on a fatter tire than a 37, if no then you are just going to lower your bottom bracket and make ride quality worse - in which case I would look for a new frame.
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Old 03-25-21, 01:33 PM
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650x48 is about the same height as 700x28. You will be lowering your BB height and clearance going to 650b
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Old 03-25-21, 01:37 PM
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I had this same issue with toe overlap and my 700c wheel set, and while I didn't switch to 650b because of the overlap, it was a nice surprise to not have it any longer. I went from 700x45 > 650x47(which actually measure out at 50) and I've been really happy with it(so have my hands and bum).
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Old 03-25-21, 02:01 PM
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Originally Posted by franswa
I had this same issue with toe overlap and my 700c wheel set, and while I didn't switch to 650b because of the overlap, it was a nice surprise to not have it any longer. I went from 700x45 > 650x47(which actually measure out at 50) and I've been really happy with it(so have my hands and bum).
Awesome! Did you notice any adverse effects?
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Old 03-25-21, 02:02 PM
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Originally Posted by Elvo
650x48 is about the same height as 700x28. You will be lowering your BB height and clearance going to 650b
Is there a conversion "ratio" or whatever to figure out what the similar size would be?
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Old 03-25-21, 02:05 PM
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Originally Posted by tdilf
When switching over to 650b, I would hope you could put on a fatter tire than a 37, if no then you are just going to lower your bottom bracket and make ride quality worse - in which case I would look for a new frame.
Yeah I've been drooling over a Santa Cruz Stigmata or Ibis Hakka... but probably shouldn't spend that much after having just bought the Scott 6 months ago. About how much would my bottom bracket drop assuming I use 650b x 42 or 48 tires?
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Old 03-25-21, 02:14 PM
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Originally Posted by speedyspaghetti
Awesome! Did you notice any adverse effects?

Nothing but positive effects so far! Yea, this did lower the BB but pedal strike hasn't been an issue and my bike does feel more alive.
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Old 03-25-21, 02:36 PM
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Originally Posted by Elvo
650x48 is about the same height as 700x28. You will be lowering your BB height and clearance going to 650b
So based on an online calculator a 700x37 wheelset would give me a diameter of 696mm (diameter is what I need, right? Not circumference) and a 650b x 42 tire/wheel combo would give me 668mm in diameter which is a decrease of 28mm, which is a bit over an inch - that has to be enough, right?
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Old 03-25-21, 03:13 PM
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I had a very similar thread a few weeks ago, and it is quite possibly the most helpful, thoughtful collection of replies I have ever experienced on Bikeforums:

Should I get 650b wheels?
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Old 03-26-21, 02:23 PM
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Originally Posted by speedyspaghetti
So based on an online calculator a 700x37 wheelset would give me a diameter of 696mm (diameter is what I need, right? Not circumference) and a 650b x 42 tire/wheel combo would give me 668mm in diameter which is a decrease of 28mm, which is a bit over an inch - that has to be enough, right?
... Then divide by two to get 14mm/side, so 14mm less height, and 14mm father from your toe. I looked up your BB drop as 67mm, which isn't terribly deep (my bike is 61mm and advertised as dual wheel compatible). You should be ok with the swap as long as you have the side clearance? Also I'm a complete lay person on this since I haven't tried 650b.
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Old 03-27-21, 03:07 PM
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650b on that frame is going to increase pedal strikes. The BB is not so high.
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Old 03-28-21, 07:06 AM
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When I look at that bike's geometry it shows a pretty high bottom bracket at 11.1 inches. This of course changes with different tires. Also don't confuse bottom bracket height with bottom bracket drop. The first is dynamic, the second is static. By looking at bottom bracket drop, 67 mm, that is what you would normally find on a 650b bike anyway.

I would have no qualms of changing to 650b and if it was my bike that would be the first thing I would do. Pedal strike is so over rated. In racing it is of concern, for the average gravel cyclist it will never be an issue. If I had to choose between the rare possibility of pedal strike over toe overlap, I will take pedal strike every time.

The issue of trail was raised above and that may or may not be of concern. Sometimes it is just a matter of trying and seeing if you can live with it. I have done quite a few 700 to 650 conversions and it has never bothered me. Most times I don't notice, especially with the type of riding I do. On my Trek Domane I noticed, the bike was different but I get used to it quick.

I think you are on the right track of fixing your problem. Good luck.
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