Correct chain length?

[Aedon]

I have changed the drive system on my  bike. When in bottom gear the chain scrapes on the bottom of the rear derauler so I will obviously have to shorten it. How do I calculate how many links to remove?

[Johan Bornman]

You don't want to calculate it. It's not a simple formula.  Shift to the biggest sprocket in front and biggest at the back. Now shorten the chain until your derailer cage makes a 45 degree angle with the horizontal. In 99% of the cases this will  be the ideal length of the chain, ensuring that it doesn't scrape in the configuration you describe.

 

Whilst youre at it, put a removable link in there.

Johan Bornman2008-08-28 03:56:50

[AndreZA]

When you purchase a new chain, it usually comes with extra length so that it is compatible with most drivetrains. How do you know how much length your bike will need? Well, it?s really quite simple?

The first step is to wrap the chain around the largest sprockets on the front and rear, so that the ends meet on the largest front chainring. For this step, it really important to not run the chain through the rear derailleur.

Next, position the chain on the chainring?s teeth at the tightest spot you could connect the chain. Now add one whole inner and outer link, so that you have approximately one extra inch of slack in the chain. That will be the optimal length for most systems.

http://bicycletutor.com/calculate-chain-length/

 

 

[Aedon]

Thanks,  Johan and Mampara.

Will give it a shot tonight.

[Racer X]

And if your really bored you can count how many links are on your old chain and then make em the same length. Use this as a last resort, Mampara's and Johan's idea is easier

[Minion]

 

And if your really bored you can count how many links are on your old chain and then make em the same length. Use this as a last resort' date=' Mampara's and Johan's idea is easier[/quote']

Or just lay the old chain next to the new chain and cut to suit. Just make sure the pins are approximately lined up. Otherwise, if your old chain is really worn, you might be out by a link or two.