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how many cogs possible on 126mm freewheel hub?

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how many cogs possible on 126mm freewheel hub?

Old 11-09-16, 11:55 AM
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how many cogs possible on 126mm freewheel hub?

I have an old 1989 mountain bike that has a 126mm hub with a 5-speed freewheel. Will the hub work with 6-speed and 7-speed freewheels or is it limited to 5-speed? Sheldon's website mentions 7-speed freewheels fitting on 126mm hubs but doesn't state if that's universal or just some hubs.
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Old 11-09-16, 11:57 AM
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I know the 'Ultra' Suntour freewheels were meant to allow more than 6 cogs in the freewheel with 126 spacing. They also require a slightly narrower chain.

Edit: I believe all 6-s freewheels are designed to work with 126mm spacing, along with most 7-s. I think the Ultra freewheels are actually meant to allow 6 cogs on 120 mm spacing. Sorry for the confusion.

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Old 11-09-16, 11:59 AM
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7-speed freewheels fit on a hub with 126 spacing.

8 and up require 130.
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Old 11-09-16, 12:02 PM
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Up to 7 will work for 126 mm. Caveat that some frames might be a tight squeeze depending on the "stack height" of the 7 speed freewheel, meaning the chain and or small cog might rub on the dropout. I had that problem with my Tommasini, ultimately getting a Regina CX to work. There's a thread around here somewhere about it.
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Old 11-09-16, 12:23 PM
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With a freewheel hub, any freewheel (FW) can screw onto any hub. (As long as were are talking the common English threads that all Japanese and Italian and SunRace and ... FWs use. Old French - be careful!) It is then just a matter of arranging the spacers (and perhaps swapping out the axle itself) to get the hub to be positioned to put that FW in the proper location.

Seven speed FWs have the narrow spacing of the early Ultra 6 FWs of the late '70s and will fit in the 126 mm dropout spacing of the traditional 6-speed bikes so you should be good on that score. If your hub was sold as a 126 spaced 6-speed hub, you should be just fine. But look at how close the small cog is to your dropout and stays. It is possible you may need to take one thin spacer from the left side of the axle and put it on the right or simply add a new spacer. Adding a spacer will make getting the wheel in a little harder. Moving a spacer left to right will redish the wheel a hair. Perfectionists will say you have to loosen the left spokes, tighten the right and retrue. Realists will say that if you never think of it again, you will never notice the difference.

I reread your post. I was thinking road bike. A 126 road bike would have a 6-speed hub ready to go. Mountain bikes use wheels with less dish as this makes for a stronger wheel, hence they use the wider road 6-speed dropout spacing, 5 speed FWs and less dish. (I am guessing this. I have no experience with mountain bikes but I have known they have used wider frame spacing for years which makes perfect sense if you are an engineer and think about the abuse those wheels get on mountain bikes.) You could go to a narrow 6-speed making no changes to your hub dishing and spacers. You could go to old 6-speed spacing and use a 7-speed FW but this will require moving a significant amount of spacers and a redish of the wheel. (And a step down in wheel reliability.) If it is a steel frame, you could respace it to 130 mm, put in a longer axle and spacers, screw on a 7-seed FW and have a good strong mountain 7-speed.

I am sure other posters more familiar with mountain bikes will have moer (an better) to say.

Ben
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Old 11-09-16, 01:38 PM
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I've done it to road bikes with QR axles. Need a longer axle & at least one spacer. Spread the rear dropouts & mount it up. Hope that limit screws & cage length on RD will work with bigger freewheel. Some will say you don't need a longer axle. But, if you only have a couple mm's making contact with the dropouts - that's not good. I like to have at least 4mm on both sides. (Forget about everything I just said if you've got a solid axle back there).
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Old 11-09-16, 01:46 PM
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Originally Posted by Spaghetti Legs
Up to 7 will work for 126 mm. Caveat that some frames might be a tight squeeze depending on the "stack height" of the 7 speed freewheel, meaning the chain and or small cog might rub on the dropout. I had that problem with my Tommasini, ultimately getting a Regina CX to work. There's a thread around here somewhere about it.
Yup. I have had mixed results with 7 speeds on a 126mm OLD axle -- sometimes you need that additional 1 or 2 mm on the drive side to prevent chain rub. (Not having a dork disk helps immensely, of course, but even that is not always sufficient.)
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Old 11-09-16, 02:08 PM
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While 7 cogs is certainly possible, and 8 may even be finagled into working, keep in mind that there's a reason why a 1989 MTB has a 5-cog cluster. The more cogs you pile on the back, the further the locknut is from the bearing, creating a longer lever arm for axle flex and exacerbating axle fatigue and eventual failure. This is more of an issue with MTBs than road bikes, as off-road conditions are harder on axles than most roads. Depending on the type of riding you intend to do, trying to maximize the number of cogs may not be the best idea.
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Old 11-09-16, 02:10 PM
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Thanks for the replies! Every bike I've owned has been 135 spacing with a 7,8 or 9 cog cassette so this older stuff is a mystery to me. After posting, I looked up the catalog (1989 Univega Range Rover ES) and it lists the bike as being equipped with a 6-speed freewheel. I could have sworn I counted five but the election kept me up much of the night and I'm a little foggy.

I'm hoping to us the Univega as a donor bike and use the rear wheel on a 1984 Trek 830 ATB frameset that I might be purchasing in the near future. I've got a 135 rear 26" wheel and at one time I had an 83 MTB that I had cold-set to 135 and I later mangled the chainstays. I don't know if the cold-setting had anything to do with the later chainstay damage or if it was all due to my mechanical ineptitude. That's why I'm a bit reluctant to consider cold-setting the Trek. It's a bit of a Grail bike for me and I don't want to do anything to jeapordize it's condition.
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Old 11-09-16, 03:35 PM
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This is very useful: Sheldon Brown's Bicycle Frame and Cassette Spacing Crib Sheet
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Old 11-09-16, 06:24 PM
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I dug up the thread which has excruciating details on my 7 speed freewheel problem. Nevertheless a lot of useful info in it.

https://www.bikeforums.net/classic-vi...l-problem.html
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Old 11-10-16, 04:48 AM
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Some good suggestions but several things to consider:

There was never much of a real width standard for freewheels.

I have a milk crate full of freewheels and even some of the same model, same brand freewheels vary in width by as much as 2mm!

Some have deeper reliefs in the back side, some are flush.

5 speed freewheels run from 24mm to 26mm wide.

The bottom picture shows a comparison of standard 6 speed, narrow 6 speed and a narrow 7 speed freewheels. These dimensions vary!

There were lots of variations in the "D" width dimension on hubs - see attached drawing. The width of old hubs was frequently modified by adding or removing washers so they would better fit a frame.

You can run into interference problems on some frames because the chain can hit or rub on the end of the seat stay and sometimes the chain stay. I've filed a little material off the tube ends to provide some clearance on lots of frames.

Trial and error is usually the best way to tell. If you can get another 126mm wide hub with a 6 or 7 speed freewheel you can easily measure the clearances and dimensions.

Last consideration, get a new chain made for 6-7-8 speed freewheels. I like SRAM PC870 chains but there are other good ones available.

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Attached Images
File Type: jpg
Freewheels126mm.jpg (77.6 KB, 241 views)
File Type: jpg
7SpeedFW-Widths.jpg (40.0 KB, 241 views)
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Old 11-10-16, 05:47 AM
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Originally Posted by corwin1968
After posting, I looked up the catalog (1989 Univega Range Rover ES) and it lists the bike as being equipped with a 6-speed freewheel. I could have sworn I counted five but the election kept me up much of the night and I'm a little foggy.
So somebody squeezed a 5-sprocket FW into the space intended for a 6? Can you do that?

FWIW, my Motobecane has 124mm spacing so I tried two different 6-spd's. Neither fit because the seat stay bulged out too much to the inside. But the FW's were different enough that one almost fit while the other clearly didn't.
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Old 11-10-16, 06:59 AM
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There were anomalies like the 8 speed Sachs Maillard Helicomatic freewheel which did fit 126 spacing, friction only.
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Old 11-10-16, 08:20 PM
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Originally Posted by jimmuller
So somebody squeezed a 5-sprocket FW into the space intended for a 6? Can you do that?

FWIW, my Motobecane has 124mm spacing so I tried two different 6-spd's. Neither fit because the seat stay bulged out too much to the inside. But the FW's were different enough that one almost fit while the other clearly didn't.
My freewheel is 6 cogs. I just remembered it incorrectly.
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Old 11-11-16, 04:28 AM
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Thank you for a very helpful comment. This type of response is the reason to hang out here.

Originally Posted by verktyg
Some good suggestions but several things to consider:

There was never much of a real width standard for freewheels.

I have a milk crate full of freewheels and even some of the same model, same brand freewheels vary in width by as much as 2mm!

Some have deeper reliefs in the back side, some are flush.

5 speed freewheels run from 24mm to 26mm wide.

The bottom picture shows a comparison of standard 6 speed, narrow 6 speed and a narrow 7 speed freewheels. These dimensions vary!

There were lots of variations in the "D" width dimension on hubs - see attached drawing. The width of old hubs was frequently modified by adding or removing washers so they would better fit a frame.

You can run into interference problems on some frames because the chain can hit or rub on the end of the seat stay and sometimes the chain stay. I've filed a little material off the tube ends to provide some clearance on lots of frames.

Trial and error is usually the best way to tell. If you can get another 126mm wide hub with a 6 or 7 speed freewheel you can easily measure the clearances and dimensions.

Last consideration, get a new chain made for 6-7-8 speed freewheels. I like SRAM PC870 chains but there are other good ones available.

verktyg

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Old 11-12-16, 03:49 AM
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Originally Posted by jimmuller
FWIW, my Motobecane has 124mm spacing so I tried two different 6-spd's. Neither fit because the seat stay bulged out too much to the inside. But the FW's were different enough that one almost fit while the other clearly didn't.
Jim,

For many years the French standard for 5 speed rear hubs was 122mm wide. At some point they started making 124mm wide hubs - before 126mm hubs became the De rigueur standard for 6 speed freewheels (later 7 speed narrow too).

Many older rear hubs had the widths changed by adding or removing washers to better fit in a particular frame....

I've been gradually putting together a 1970 Motobecane Grand Record - just have to put on the pedals and tape the bars.

I like 13-28T 5 speed FWs for my classic bikes but good one are getting expensive and hard to find in French thread. I had a very nice Atom 77 13-28T 6 speed narrow freewheel.

Everything looked like it would fit without any problems but I had to add a 1mm spacer behind the freewheel for spoke clearance.

That reduced the clearance between the small sprocket and the dropout so I added a 1mm washer to the drive side of the 122mm wide Normandy Luxe Competition hub.

Next, the bottom inside of the seat stay interfered with shifting up from the small cog. Had to resort to the old fix: file enough clearance into the seat stay.

Domed stays have enough metal where the dropouts enter the stay that filing 2mm-3mm off at an angle wont cause any problems. See pictures.

Square end stays may not have enough braze up in the tube so be careful when modifying them.

Everything is working great now but I had to play around with chain length and axle position to get the Campy NR derailleur to play nice with the 13-28T FW and 50-38T chainrings.

verktyg

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Last edited by verktyg; 11-12-16 at 03:57 AM.
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