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Converting 5 sp to 7 sp how much to widen rear triangle

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Converting 5 sp to 7 sp how much to widen rear triangle

Old 08-20-21, 05:39 PM
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sortieavelo
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Converting 5 sp to 7 sp how much to widen rear triangle

Hi all, Im hoping to convert this sweet old fuji 10 sp to a 650b ride. But my 650b rear wheel is a 7/8 Shimano and is too wide for the frame. Rear dropouts are about 125mm? And new rear wheel looks to be about 140mm. My question isnt so much how to widen dropouts (Im going with the RJ bike guy threaded rod method) but more whats the rule of spacing between the smallest cog and the right chainstay? Do you go by a set range of mm/inches btw cog and frame or do you just go by the chain line?




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Old 08-20-21, 05:45 PM
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If it were my bike, I would not respace the frame at all. I would remove that big honkin' spacer on the left side of the hub, trim that amount off the axle, and re-dish the wheel so that it will fit in the bike with a minimum of effort. The cassette will overhang the end of the freehub body, so you need a couple mm of locknut sticking out...

Unless you're mountain biking, 7-speed *should* be 126mm in my book.
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Old 08-20-21, 05:57 PM
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If you just want to go to 7 speed, there is no need to mess with the frame. Just swap to a 7 speed HG hub. The RSX, RX100, 105 and 600 groups all had 7 speed HG hubs in 126mm width. Another option is to buy a 7 speed freehub body and swap it onto your existing hub.

Another way is to take the original freewheel hub that came with the bike, and swap a 7 speed freewheel on there. You might have to reshim the hub to the left though.
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Old 08-20-21, 08:19 PM
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I found an old Trek 620 frame with a 5 speed Helicomatic hub, and 126 mm spacing. I also found an old 7-speed freewheel hub with 126 mm spacing. Good, easy match.
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Old 08-20-21, 09:44 PM
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Originally Posted by ThermionicScott View Post
Remove that big honkin' spacer on the nds. Hacksaw the axle. Re-dish the wheel.
^ This!

And hope your spokes are long enough/not too long, 'cause that's a huge spacer.
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Old 08-22-21, 02:18 PM
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thank you. Is the 126mm spacing measured from outside of R hub to outside of L hub?



Originally Posted by andrewclaus View Post
I found an old Trek 620 frame with a 5 speed Helicomatic hub, and 126 mm spacing. I also found an old 7-speed freewheel hub with 126 mm spacing. Good, easy match.
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Old 08-22-21, 03:05 PM
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Originally Posted by sortieavelo View Post
Is the 126mm spacing measured from outside of R hub to outside of L hub?
Sheldon is your go-to on hub spacing (o.l.d.) and most all things basic or vintage:

https://www.sheldonbrown.com/frame-spacing.html
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Old 08-22-21, 04:05 PM
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I have a different view. I would respace the frame to the likely 135 that the new hub has. This way the wheel dish won't become way steep. Or in other words the spoke tension difference between the two sides of the new wheel will remain less then if the spacer is removed and the RH spokes need further tightening to shift over the rim into the "new dished: centering. Of course this assumes that the OP knows how to respace the frame so the rear end is still centered and the drop outs remain parallel to each other. Andy
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Old 08-22-21, 04:51 PM
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Originally Posted by SurferRosa View Post
Sheldon is your go-to on hub spacing (o.l.d.) and most all things basic or vintage:

https://www.sheldonbrown.com/frame-spacing.html
that was SUPER helpful. Thank you. Now I need one of those calipers w the long arms!
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Old 08-22-21, 05:26 PM
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Originally Posted by sortieavelo View Post
Now I need one of those calipers w the long arms!
Those are good tools to have on hand. My super cheap one from eBay (under $4) works great. However, you can usually measure the o.l.d just by using a table top, metric ruler, sheet of paper, and a pencil. Or put the hub in your rear dropouts and compare those two measurements (o.l.d and frame) using the ruler. If the hub is in a wheel it can be a little more tricky.
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