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650B Conversion / 6 spd to 10?

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650B Conversion / 6 spd to 10?

Old 06-29-08, 07:21 PM
  #1  
therentedmule
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650B Conversion / 6 spd to 10?

Back story:
I have an old road bike with 700c wheels and almost no clearance between tire and brake stay, fits size 25 tires if not too thick (I am currently running Armadillos in size 23). The rear is a 6 speed freewheel with a bent hub and a newly broken spoke. I'm thinking it's time for a new wheel. I found a guy that will build me a set for $283+ (he has some never been used 7 speed hubs) but...

Question:
If I do a 650B wheel conversion is there any way to make room for a larger freehub that can accommodate a 9 or 10 speed cassette?

I may do the conversion regardless because I would like to get fenders on this bad boy. I vaguely remember reading a post once stating that it was possible to "stretch" the rear fork so as to use a contemporary freehub. Is this doable? Would this significantly compromise frame strength? Any thoughts?
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Old 06-29-08, 08:01 PM
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HillRider 
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Since your bike is a 6-speed, the rear dropout spacing is most likely 126 mm while current 8/9/10-speed hubs are 130 mm. Further assuming your frame is steel, the width is easy to change by "cold setting" the frame to the wider spacing and any bike shop can do it or you can do it yourself. Sheldon Brown's web site (www.sheldonbrown.com) has detailed directions. BTW, cold setting an Aluminum frame is not recommended and a carbon frame is out of the question but there were very few 6-speed Al frames and NO carbon frames of that vintage.

Or you could do nothing. Flexing the frame by thumb pressure alone will let you install a 130 mm hub in a 126 mm frame. It's a bit of a struggle but quite managable. Even an Al frame can be used this way.

The big issue with changing from 700c to 650b wheels is brake alignment. 650b rims are 19mm smaller in radius than 700c rims so you will have to lower the brakes that far to align with them. Cantilever mounting posts would have to be cut off and rebrazed or caliper brakes with a very long reach or suitable drop bolts will have to be found.
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Old 06-29-08, 08:29 PM
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In my experience on the few bikes I've tried it on, a rear triangle with 126mm spacing can be easily spread to accept a 130mm hub (the width you'd need to get a 8/9/10 speed cassette in there). You shouldn't even have to worry about cold setting the frame as it will likely easily spread the 2mm per side with minimal force. Frame strength should not be an issue unless your frame had problems to begin with.

You might want to do a search on cold setting though as others experiences have differed from mine.
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Old 06-29-08, 10:03 PM
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Ah yes, the bike is in fact a 6 speed aluminum. A Univega Viva Tech a budget version of the popular steel Viva Sport, circa 1989 (or so the internet tells me). The brake issue I was aware of. I have side pull calipers, they may even fit 650B as they are adjusted all the way to the top at the moment and if not I suspect finding ones that fit should not be difficult given the position of the stay.

I may just go for it spread it myself.
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Old 06-30-08, 07:22 AM
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HillRider 
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Originally Posted by therentedmule View Post
The brake issue I was aware of. I have side pull calipers, they may even fit 650B as they are adjusted all the way to the top at the moment and if not I suspect finding ones that fit should not be difficult given the position of the stay.
Most sidepull calipers have a 10 mm total adjustment range and you need 19 mm. You will almost certainly need new, longer reach brakes.
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