Chain measurement..

[mickeyc]

Can someone give me a way to measure for a chain? I have an old skip tooth bike that needs a chain but all I have is a bunch of 1/2" pitch chains. Tried using one of them to go around the sprockets but with it not fitting the teeth properly, it's difficult to tell what I need for actual length. A 55" 1/2" pitch came up a couple (about 3 or 4) inches short but again hard to tell as it didn't fit the teeth on the sprockets. The rear sprocket on the wheel is an 11 tooth, a bit bigger than normal I think but one I want to use.

Any help greatly appreciated.

 

[Archie Sturmer]

An approximation that I use considers the sprocket sizes and the frame measurements; (assumes normal tire clearance).
Half the number of teeth of both sprockets, (e.g., half 26 + 11 = 18.5") plus 2-times the distance between the center of the bottom bracket, and the axle sweet-spot on the rear drop outs or forward-release fork-ends, (e.g., 18.75" x 2 = 37.5"). If a fraction results for the overall result, then round-up to nearest 1".
The half-X factor is because the chain only contacts about half of the teeth at one time; the 2-X factor is to account for the upper and lower segments of chain, between the 2 sprockets. The round-up is due to steel chains not stretching during installation, and the rear drop outs (or forward-release fork-ends) allowing for adjustment for a longer chain, (i.e., axle sweet-spot).
It is an approximation-only, mostly because of the angles of the chain line, and less-so their tangents to the sprockets.
For a perfect un-worn chain, the length (e.g., 18.5" + 37.5" = 56"), in inches, would equal the number of link pairs (e.g., 56 big and small).
Worn chains may measure in-inches more than the number of link pairs.

For half-inch pitch chains the general method is similar, with some math differences due to the number of teeth per inch, and allowance for half-links.

 

[bloo]

...

 

[piercer_99]

for a boys bike, they were typically 56", in my experience. most of the girls I have had the chain off of, were 54".

both my Pierce's and my Westfield, with 28" wheels, are 56" chains. I have 2 with 26t chain wheel and 10t rear cog, from center of crank to center of rear axle it is 18-5/8". The one with an 11t rear cog, is 18-3/8" center of crank to center of axle.

My brides 41 Elgin ladies ballooner has a 54" chain on it.

None of the chains are stretched, they have dead on measurements to them.

Good luck.

 

[mickeyc]

WOW...thanks for the info. Will give that a try for sure. Stand by for results....

 

[mickeyc]

Just did my measuring, came up with this....26 tooth plus 11 tooth divided in half equals 18 1/2". My frame must be a bit longer than the examples above as it measures 20" from middle of BB to middle of axle. That gives me a measurement of 40" plus 18 1/2" is 58 1/2" or rounded to 59". So now I need to get a 59" skip tooth chain.
Agree?

 

[Archie Sturmer]

Sounds longer than most but a good estimate. If the axle could be moved forward by a fraction or so, maybe a 58” might squeeze on? Not sure how common 58” or 59” chains are, but I believe that a member Scott McC had some Diamond No. 61 1” pitch 3/16” wide roller links, that may each be used with a (separate) master link, to add length to a shorter chain.

 

[mickeyc]

Guess I'll see what I can shake out in the parts wanted section. Thanks again for your help.