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Talk to me about 650b/27.5 wheels
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I have a Santa Cruz Stigmata gravel/cross bike that will clear 700x40mm tires, but if I mount anything more than 35mm, I felt the wheels are too big and unwieldy, and also causing toe clearance problems. That got me thinking about putting some 650b wheels. Unfortunately by the look of it, the rear chainstays will probably only clear 40 or even less for smaller diameter (see the picture below). In that case, is it still worth going to 650b?




Last edited by: dalava: Feb 21, 19 7:50
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Re: Talk to me about 650b/27.5 wheels [dalava] [ In reply to ]
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well they make 650b x 38 so that might work for you.. granted not all brands will have that size. My smallest 650b tire is 42mm (Donnelly MSO) they are 43.5mm on 24mm wide internal rims. My WTB byways are now 48.1 on 27mm internal rims...but they are a little over inflated currently. I have a Parlee which is supposed to clear 700x40 and like your stiggy is more of a CX bike then one that was designed for 650b. I have almost no clearance ~1.5mm when running the 47mm Byways so I stay away from mud when running those.
Last edited by: spntrxi: Feb 21, 19 8:43
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Re: Talk to me about 650b/27.5 wheels [dalava] [ In reply to ]
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You're going to reduce the trail of the front end making the bike quicker to respond. How much depends on the exact geometry.

Make sure you are OK with that.

Since a 650B rim is 38mm smaller than a 700C rim, the radius will be 19mm smaller putting that rear tire closer to the narrower part between the chainstays.

With that said, try ro borrow a set of wheels and see if it fits.
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Re: Talk to me about 650b/27.5 wheels [jaretj] [ In reply to ]
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Yeah, that's what I am going to do, borrowing a set with at least 40mm and see how they fit. I think the front-end control won't be an issue.
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Re: Talk to me about 650b/27.5 wheels [dalava] [ In reply to ]
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dalava wrote:
Yeah, that's what I am going to do, borrowing a set with at least 40mm and see how they fit. I think the front-end control won't be an issue.

good idea... I couldn't find anyone so I bought a cheap set ~$400 then upgraded. Ofcourse I knew I had room for 42's easy peasy.
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Re: Talk to me about 650b/27.5 wheels [dalava] [ In reply to ]
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I switch tire and wheel sizes quite a bit on my mixed condition bike. I have a custom bike and it was built around performing best (handling wise and rough road wise) with 700x38 and 650x42 setups. In 650x42 mode, the wheel diameter is closer to the equivalent to a 700x25mm setup, so the trail is lower and consequently handles a little quicker and snappier. One thing I have found using the smaller wheel size with wider tires (42mm) is that: even though the trail is reduced and the steering is quicker, this effect is somewhat offset with the extra rubber on the ground - so the quicker steering settles down with the more "grabby" rubber on the ground and you get the benefits of more natural turning and retaining the snappy bike feel - plus the volume for rough surfaces.

I'm not sure what a smaller 650 setup would feel like, but I suspect the handling would be worse and maybe a little too twitchy. On the other extreme, I frequently used 650x48mm and they definitely make the bike handle different on the road. Cornering isn't as precise and the amount of rubber on the road is noticeable in terms of self-steer (depending on pressure). They perform very well in rough conditions though where volume is your friend.

Edit: keep in mind, the BB height will be a lot lower going from 700x38 to 650x38 - could be a serious pedal strike issue.

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Last edited by: Bonesbrigade: Feb 21, 19 11:14
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Re: Talk to me about 650b/27.5 wheels [Bonesbrigade] [ In reply to ]
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The SC Stigmata BB drop is 69mm and I use a 170mm crankarm, so that won't be an issue. What I am worried the most if where the chainstays pinch in, I am not sure if anything bigger than 40mm will fit, and if not, it may not be worth going to 650b because I would like to run wider tires.
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Re: Talk to me about 650b/27.5 wheels [dalava] [ In reply to ]
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dalava wrote:
The SC Stigmata BB drop is 69mm and I use a 170mm crankarm, so that won't be an issue. What I am worried the most if where the chainstays pinch in, I am not sure if anything bigger than 40mm will fit, and if not, it may not be worth going to 650b because I would like to run wider tires.

BB drop and BB height from the ground are two separate things. The drop refers is in relation to the axle height. A smaller wheel/tire diameter will lower the whole bike, thus lowering the bb height. Pedal strikes can definitely be an issue depending how and where you ride it using smaller wheels and tires.

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Re: Talk to me about 650b/27.5 wheels [Bonesbrigade] [ In reply to ]
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So if I am ok with 700x25 now in cross setup, then 650x42 would get me to the same BB height, right?
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Re: Talk to me about 650b/27.5 wheels [dalava] [ In reply to ]
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dalava wrote:
So if I am ok with 700x25 now in cross setup, then 650x42 would get me to the same BB height, right?

Yep, they are about the same. I’m pretty sure your stigmata will do 650x42. I have a friend that’s runs that, but not sure what frame year he has.

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Re: Talk to me about 650b/27.5 wheels [Bonesbrigade] [ In reply to ]
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So I measured the narrowest point where the chainstays pinch in, it's 46mm wide. Would I be able to run tires that will actually measure to 42mm wide when inflated?
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Re: Talk to me about 650b/27.5 wheels [dalava] [ In reply to ]
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dalava wrote:
So I measured the narrowest point where the chainstays pinch in, it's 46mm wide. Would I be able to run tires that will actually measure to 42mm wide when inflated?

You should be alright - but if it were me, I'd try to test it by borrowing a 650b and see where the tire lines up.

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Re: Talk to me about 650b/27.5 wheels [dalava] [ In reply to ]
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dalava wrote:
So I measured the narrowest point where the chainstays pinch in, it's 46mm wide. Would I be able to run tires that will actually measure to 42mm wide when inflated?

this is rim/tire dependent. my 42's ballon to 43.xx on 24mm internal as I stated but I have not measured them in a few weeks. The might have grown.

if you have tires that actually measure 42 you could run them, but I wouldn't do any mud.
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