So, I’m a complete amateur. This is my first proper project (lockdown special). I’m converting a late 80’s “racer” into single speed. I don’t think I can use the really good bb in it as too long? I think ss need shorter bb’s? I think I have Shimano 600ex 113mm and think I cannot use as too long for chain line etc? Please help. Thanks
Six speed to ss conversion and bottom bracket length
- Thread starter Kaufman
- Start date
It's going to depend on which ss chainset you're planning on using. There is a huge range, and no easy way to sort stuff out. One place to start to get a feel of the vital statistics is Sheldon Brown's page: https://www.sheldonbrown.com/bbsize.html. And then fall down the rabbit hole of the rest of Sheldon's pages... 
The type of taper on the bb is important: the two main ones are JIS (like your 600) and ISO (mainly Italian chainsets). The bottom bracket shell is also critical (2 main types). See Sheldon. If you can work out what you need, there is a large range of pretty cheap sealed bbs on eBay (I know you don't like it) of various lengths.
If you're looking to use an old chainset, it's worth asking on here if anyone knows what bb you need.
Depending on how you're planning to set up the chainline, you can use a double chainset to run single speed (put spacer washers in instead of the 2nd chainring). You've got scope with 126mm rear spacing. I've done that in the distant past (when I lived in flat Cambridge).
Nick
The type of taper on the bb is important: the two main ones are JIS (like your 600) and ISO (mainly Italian chainsets). The bottom bracket shell is also critical (2 main types). See Sheldon. If you can work out what you need, there is a large range of pretty cheap sealed bbs on eBay (I know you don't like it) of various lengths.
If you're looking to use an old chainset, it's worth asking on here if anyone knows what bb you need.
Depending on how you're planning to set up the chainline, you can use a double chainset to run single speed (put spacer washers in instead of the 2nd chainring). You've got scope with 126mm rear spacing. I've done that in the distant past (when I lived in flat Cambridge).
Nick
Re:
It also depends on the wheels and type of single speed, whether screw on in place of a standard freewheel which I know little about or later wheel with freehub where there is more flexibility as to where the spacers are which is what I do on my MTB single speeds. I guess with 126mm rear it's probably screw on. My point is you have to look at the whole picture, I would say the first iteration does not need to be perfect. On a normal 12 speed you only have a "perfect" chain line in two gears, just make sure not too far off.
Coincidentally in the distant past I ran a fixed gear while living in Cambridge - it is a great place for a fixed as it is very flat ! I had a wheel built with a flip flop hub, screw on one side and fixed the other. Wheel's still going strong although the bearings are a bit rough. The line was reasonable with just a slightly shorter axle although can't remember the details - it was over 30 years agochinr
Oh, you can also get chainring bolts for single speed that are shorter and don't need spacers. Stronglight make them for sure as I have a set.
It also depends on the wheels and type of single speed, whether screw on in place of a standard freewheel which I know little about or later wheel with freehub where there is more flexibility as to where the spacers are which is what I do on my MTB single speeds. I guess with 126mm rear it's probably screw on. My point is you have to look at the whole picture, I would say the first iteration does not need to be perfect. On a normal 12 speed you only have a "perfect" chain line in two gears, just make sure not too far off.
Coincidentally in the distant past I ran a fixed gear while living in Cambridge - it is a great place for a fixed as it is very flat ! I had a wheel built with a flip flop hub, screw on one side and fixed the other. Wheel's still going strong although the bearings are a bit rough. The line was reasonable with just a slightly shorter axle although can't remember the details - it was over 30 years agochinr
Oh, you can also get chainring bolts for single speed that are shorter and don't need spacers. Stronglight make them for sure as I have a set.
Re:
I would say before you go and blindly buy a whole load of kit, hoping that it will be the optimum fit, just assemble what you have and you then have a set up as a point of reference. You can then see that it needs a BB axle 5mm shorter or whatever and what you subsequently buy is an informed purchase
I would say before you go and blindly buy a whole load of kit, hoping that it will be the optimum fit, just assemble what you have and you then have a set up as a point of reference. You can then see that it needs a BB axle 5mm shorter or whatever and what you subsequently buy is an informed purchase
Re: Re:
absolutely this, I should have said, also you can play by 5mm or so by whether the chainring is on outside or inside of chainset ie in inner or outer position, assuming your chainset allows. Mine was an old stronglight 99 so had lots of flexibility. Also be prepared to play with gearing a bit, but ride for a while before spending.
pigman":1mbnthfk said:
absolutely this, I should have said, also you can play by 5mm or so by whether the chainring is on outside or inside of chainset ie in inner or outer position, assuming your chainset allows. Mine was an old stronglight 99 so had lots of flexibility. Also be prepared to play with gearing a bit, but ride for a while before spending.
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