Single-speed Chain-length Calculator?

Postby hagfish on Sun 21/Sep/14 11:06am

Years ago, I converted my commuter bike to a singlespeed. I run the original triple chain ring on its largest cog (48-tooth), back to an 18-tooth sprocket. By happy accident, it's the perfect chain length, and I don't need a tensioner.

The gearing is a bit short for my cruising speed, and I find myself bobbing out, so I would like to run a smaller sprocket, but I would also like to retain the 'perfect' chain length.

There are lots of ratio calculators out there, but I am wondering if there's a chain-length calculator - one that will tell me which ratios will lenghen/reduce the overall chain length by an even two links, given that 48/18 is a starting 'perfect' length. I expect the only way to be sure will be to break out a bunch of sprockets and my chain-whip :)
Member for: 11 years 5 months

Re: Single-speed Chain-length Calculator?

Postby Simonius_Titius on Sun 21/Sep/14 3:05pm

Here you are:
Given the chainstay length this gives you the exact chain length for each combo, so you can see whether it is within your wriggle room in the dropouts.

The amount of slop is also calculated but only in the downloadable version of the program:

Measuring your chainstay length accurately enough might be hard, it may be easier to work it out backwards from your chain length and how much slop you have with a new chain and good sprockets. gives both the simple and the exact formulas. The simple one should be fine for you.
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Member for: 12 years 0 months

Re: Single-speed Chain-length Calculator?

Postby hagfish on Sun 21/Sep/14 4:19pm

Thanks for these links - that's just what I was after. I shall have a play.
Member for: 11 years 5 months

Re: Single-speed Chain-length Calculator?

Postby musta on Sun 21/Sep/14 9:15pm

There are so many ways to get around this, having made countless single speeds myself all with tensioners.
You have to also factor in that a chain will lengthen over time as it wears...
It sounds like you are riding on the road, for a SS commuter you don't really have to have as much tension compared to a mountain bike.


1) use single speed specific rear sprockets in particular - greatly increase chain retention even with a slightly loose chain. (don't just use one from a cassette, the ramps etc cause easy chain loss and the teeth aren't that high)
2) half links for chains
3) filing dropouts / filing axles

or the expensive eccentric bottom bracket.

see my ghetto eccentric bolt up axle I made. still yet to see anything similar.
Had zero issues with it, even ran it will a disc brake so alignment was perfect.
Member for: 12 years 1 month

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