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converting 120mm hub to 126mm....

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converting 120mm hub to 126mm....

Old 06-27-22, 12:17 PM
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ehcoplex
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converting 120mm hub to 126mm....

I've got an early Shimano 600 hub that's 120mm I want to convert to 126mm (that's the frame's spacing & I want to use a 7sp freewheel). I've got the longer axle for it. I haven't built the wheels yet. Do the additional 6mm of spacers all go on the drive side? Is there any reason any spacers would get added to the NDS? I'm assuming the answers are yes, & no to these questions, but we all know what happens when assumptions are made.... And again, I haven't built up the wheels yet, so dishing will be dealt with when I do.... THX
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Old 06-27-22, 12:24 PM
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My approach would be to put the center of the hub as close to the center of the bike as possible. That would take into account the limiting factor of the freewheel dimensions. How close can you get the freewheel to the stays? The other consideration is chain line. Do you line up (chain line) the freewheel with the Crank set to avoid spacing the crank set?
Why? to minimize the offset of the hub from the center of the bike which in turn minimizes the difference in tension between the DS and NDS spokes.
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Old 06-27-22, 12:47 PM
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Campy hubs add all the spacing to the right/drive side FWIW

and there is plenty of room then for 7 spds
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Old 06-27-22, 12:55 PM
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- Put all additional spacers on the ds.
- Build wheel accordingly, but do not fully complete.
- Make fine adjustments to spacing with the freewheel and chain in place.
- Complete wheel build.
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Old 06-27-22, 03:53 PM
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I converted a Campagnolo Gran Sport hub to 126mm 7 speed recently (Sunrace 13-28 freewheel).
I found measuring the hub and cones and making a spreadsheet to play with the spacing worked.
Decided which option would work best and did a dry build (no spokes or grease) - came within 0.31mm of calculated OLD - and I could then check the chain clearance on the stays.
I've found my bike needs 5.5mm from the DS locknut to the face of the small cog with an 8 speed chain


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Old 06-27-22, 08:37 PM
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Originally Posted by Aardwolf View Post
I've found my bike needs 5.5mm from the DS locknut to the face of the small cog with an 8 speed chain.
This is pretty much what you need to focus on.

According to Sheldon, 5 speed freewheels are 24.0 wide and 7 speed are 31.9mm wide. The freewheel is adding about 8mm to the DS. I’m guessing you’ll need to add the 6mm to the DS.

Measure current locknut to 1st cog. That would give you a good idea what you need on the DS between the 1st cog and the dropout.

You “might” need to add more than 6mm to the DS and remove a mm from the NDS.

John

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Old 06-28-22, 06:26 AM
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You will have to re-dish the wheel to center it. Your dropouts added 3mm per side but your hub added all, nearly all, of it is on the DS.

I’ve done some 126 to 130, more specifically 130mm OLD hubs close as I could get to fit 126mm dropouts. I have not run out of spoke threads re-dishing. The tighter you can run the 1st position cog to the dropout, with clearance, the better.

I’m sure there are others who have done the 120 to 126, with a wider freewheel, and can chime in.

John

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Old 06-28-22, 08:56 PM
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Originally Posted by 70sSanO View Post
You will have to re-dish the wheel to center it.
Not if the wheels haven't been built yet.....
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Old 06-28-22, 10:42 PM
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Originally Posted by ehcoplex View Post
Not if the wheels haven't been built yet.....
LOL! You are quite right.

I’ll rephrase that. You’ll have to “dish” the newly built wheels.

John
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