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Why not 650b??

Old 06-30-20, 05:30 PM
  #1  
showlow
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Why not 650b??

In the marketing material for my bike frame it says that 650b isn't recommended because the frame isn't "designed" for it. Given that a slightly larger tire on a 27.5/650b wheel has the nearly the exact same diameter as a 700c wheel with a smaller tire, then what could the issue possibly be? What is meant by the bike not being "designed" for 650b?

Edit- sorry, wrong forum. Possible to move to mechanics?

Last edited by showlow; 06-30-20 at 05:39 PM.
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Old 07-01-20, 09:23 AM
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friday1970
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What I know about converting to 650B is really about two things. Brake reach and pedal-to-ground clearance.
I recently converted an older Trek 330 to 650b. My only issue was the original brakes didn't reach far enough, so I had to modify the frame for modern recessed screw brakes and then use a pair of Tektro brakes that did reach. I can fit 38mm tires with no issue. I might be able to fit 42's too, but haven't tried.
I use 170mm cranks, and since the bottom bracket is high enough on this "sport touring" frame, I've had no issues with pedals hitting the ground.
So really, the frame wasn't exactly designed for 650b per se, but it does work with well as a 650b. I am loving the plush ride of larger tires and lower pressures.

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Old 07-01-20, 02:20 PM
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fietsbob
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27.5" is same as 650B smaller rim fatter tire ..
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Old 07-15-20, 05:28 AM
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shelbyfv
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Did you ever determine why?
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Old 07-15-20, 10:13 AM
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ClydeClydeson
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Could be there is no specific reason why not, but the company just never tested the frame with 650 wheels. If you put 650 wheels on and the bike handles a bit funny and you end up getting run over by a dump truck, you can't say it was their fault because they never told you not to use 650 b wheels.

If you've got 650b wheels on hand that will work, and you acknowledge that you are taking the (admittedly very small) risk yourself, then go for it.

It also could be an issue of geometric limitations. Yes, putting 42mm tires on a 650b rim will give it a similar diameter to a 700c wheel, but what if such wide tires don't fit... maybe the space between the chainstays will only allow 32mm tires at the point where 650b tires would be, so you can't physically fit the hypothetical 650b wheels with the same diameter.
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Old 07-15-20, 11:41 AM
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sean.hwy
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It's a lot easier to say no dog allowed in the park than to say "only good well behaved dogs allowed".

You have to get a lot of things right when swapping to 650b wheels. As others have said if you have rim brakes they will not work. You might be lower to the ground where you pedals might hit on some turns or terrain. Seems like most 650b rims tend to be wider ( moutain/gravel bike ) so maybe the tires or too wide. Seems like a lot of 650b wheels have 9 Spd cassette vs 700c wheels that have 11+ speeds. Of course you can get around all that but it's a lot easier to say it's not recommended.
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Old 12-26-21, 08:44 AM
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I'm pretty sure those disclaimers are CYA for someone unfamiliar with the lower BB height. Just in case someone litigious were to clip a pedal and crash in a corner.
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Old 01-19-22, 06:15 PM
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Nothing really to add to this discussion, just a comment
I'm building another classic MTB drop bar conversion and I'm stuck between getting 650b wheels or sticking with 26" and going with slicks. I'll figure it out.
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