Chain length calculator

[RunForTheHills]

Or you could just wrap the chain around your largest rear sprocket, through the derailleur, and around your largest chainring, pull it tight, and then add two links and remove the rest. That's what I do.

 

[Stefan Mikes]

Or you could just wrap the chain around your largest rear sprocket, through the derailleur, and around your largest chainring, pull it tight, and then add two links and remove the rest. That's what I do.

Yes, of course. There are many techniques. The only practical use of the formula is to know the required chain link number if case you start from the clean sheet and want to be sure what chain to buy.

 

[Elyot919]

Over the years I've modified gearing on most of my bikes. What to do about the existing chain was always an issue; longer, shorter, who knew until you could wrap it around the biggest cog and front ring. So considering another change I (finally) did the obvious and Googled 'chain length calculator'. Some don't work correctly, some reference the tried and true method I've always done, and others didn't have enough tooth count range in the calculator.

But THIS ONE seems to meet all my needs. For my current setup (48t chain ring, 42t biggest cog, and 478mm chain stay) it correctly calculates the chain at 120 links. For the 46t cog I'm considering it calculates a 122 link chain. For a 50t cog I'd need to go with a 124 link chain, both doable with the replacement 126 link chain I have in the shop. Nice to know.

Unfortunately the 50t cog would require changing the medium cage derailleur to a long cage. More studying...

BTW - My bike is a hard tail. For a FS frame you would need to additional links to these calculated results.

Calculators are great for a baseline, but you're spot on about full-suspension frames. The chain growth during rear travel can easily snap a derailleur if you don't account for those extra links.

Going up to a 50t cog is a massive jump, a long cage is pretty much mandatory there to handle all that extra slack. It's a lot of trial and error once you start modifying the stock gearing like that.

 

[Stefan Mikes]

Calculators are great for a baseline, but you're spot on about full-suspension frames. The chain growth during rear travel can easily snap a derailleur if you don't account for those extra links.

Going up to a 50t cog is a massive jump, a long cage is pretty much mandatory there to handle all that extra slack. It's a lot of trial and error once you start modifying the stock gearing like that.

I used the calculator to get the value of chain link count for my two e-bikes (38-51T and 36-46T). The results were spot on. If it were an FS e-MTB, I would have added extra 2 links to the number already calculated for the SGS derailleur cage.