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Converting Speedster to 650b

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Converting Speedster to 650b

Old 09-28-21, 03:05 PM
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bobh123
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Converting Speedster to 650b

To add to the knowledgebase:

I have a CoMotion Speedster I purchased in 2018. It came with 700c wheels (Velocity Dyad rims), and I have been running Schwalbe 700cx35 tires. Without looking, I think they are Marathon GT HS480. The actual width is around 37 mm. We are a ďheavyĒ team with combined weight around 350 pounds. We typically run them at around 70-75 psi (the maximum psi is 80)

I wanted to try 650b wheels for several reasons. The reasons arenít that important at the moment. Getting and installing the wheels has taken several twists and turns, but they are on the bike now. I have 650bx42 Panaracer Gravelking slick tires on Velocity Atlas rims. The actual width is around 42 mm. I have been running them at 55 psi (the maximum psi is 60). I was surprised that, compared to the 700c tires at 75psi, the 650b tires feel very firm at 55 psi.

The 650b tires are noticeably wider than the 700c tires. The 650b wheels feel lighter, but I havenít weighed them to be specific. Side by side, the 650b wheels are a little smaller, but not by a huge amount.

With the 650b wheels Ė
  • There is now adequate room for fenders. Yeah!
  • I have a SON dynamo hub on the front wheel with only 36 spokes (thatís as big as they come in a disc version), and the wheel feels satisfactorily strong. The 700c wheels have 40 spokes in front.
  • The bottom bracket is a little lower (theoretically around ĺĒ) so I am more careful to raise the inner pedal when going around sharp, fast turns. We havenít had any pedal strike going around modest turns at modest speeds.
  • The wider contact patch results in a little more tire noise on asphalt roads. Some of that also could reflect different tread patterns on the tires.
  • With the smaller wheels, the gearing has gotten a little easier. I havenít done the math, but it is similar to all gears shifting one position easier. Thatís good.
  • I havenít noticed any appreciable difference in pedaling effort or speed over the ground. A friend told me that smaller wheels will be harder to pedal and slower, but I havenít perceived that pedaling effort has increased and it doesnít seem that times over distances ridden with the 650b wheels are different than times over the same courses pedaled with the 700c wheels. The differences in times are close enough to be within normal variations.
  • The wider tires and lower pressure smooth out bumps, cracks, twigs and other irregularities. Going over a crack doesnít result in a sharp jolt, just a gentle nudge. Thatís nice.
  • Compared to the 700c wheels, the smaller wheels with wider tires have, I think, less trail and also less pneumatic trail effect. In combination, the effect is that the bike is more agile. Going straight is no problem. Turning is easier that with the 700c wheels. However, I find that when I turn I have the sense that the front wheel wants to turn even more to the side. Itís not neutral. It isnít a problem to control, but I am aware of it. Maybe it just another way of saying the bike is more agile. Or maybe it is just saying I am too used to higher-trail bikes and need some time to get used to it. Perhaps somone can do some calculations on trail and flop factor any be more quantitative
The tradeoff for a stronger wheel with the dynamo, room for fenders, smoother ride and lower gears so far seems to be a net positive.

So, if you are considering converting from 700c to 650b, I say ďgo for it.Ē
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Old 09-29-21, 08:55 AM
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Paul J
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Thanks for sharing this bobh123

We have a mid-teens Speedster and I've thought about 650b for a second set of wheels. Is yours the newer model without the diagonal tube and with 35c as stock?
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Old 09-29-21, 10:28 AM
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No diagonal tube. Not sure what your are referring to as "35c as stock."
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Old 09-29-21, 11:46 AM
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Originally Posted by bobh123 View Post
No diagonal tube. Not sure what your are referring to as "35c as stock."
Ours came stock with 700 X 28c tire size from the factory and wasn't really sold as a touring bike though many were using them for that. The newer ones are showing 35c in the spec sheet from Co-Motion.
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Old 09-29-21, 12:02 PM
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I don't recall what tires came with the bike. I've had 700c x 35 since the beginning. I think they were the tires that came with the bike, but don't specifically recall. That is as big as the bike will fit and still leave a little room for tires.
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