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Chainstay length calculator

urbaindk

urbaindk

The Real Dr. Science
Jul 12, 2004
4,819
0
Sleepy Hollar
sittingduck said:
I was thinking it would be really sweet if we had some kind of calculator for different chainring combos and how they work out with chainstay lengths.
Click to expand...
I saw your post in the majesty thread....

With a little rudimentary geometry I was able to put together a spreadsheet that you can enter an approximate chain stay length, front and rear sprocket size, and wheel size that will calculate the gear inches, number of links, and actual chain stay length.

I uploaded it on google docs.

http://spreadsheets.google.com/ccc?key=r8FV6xqSjdu1WM6ea6UAbFw
Please create your own copy (ctrl-shift-S) it before playing with it. Let me know if it works. If anyone wants to check the math, that would be good too!

I used some very basic assumptions such as 1 full link = 1 inch and that the circumference of a chain ring is equal to 1/2 the number of teeth. I put in a rounding function that rounds number of chainlinks to the nearest 1/2 link.

It's very basic but it should give a good estimate. In other words, don't be a dumbass and cut your chain based on this calculation and come back and blame me later. Check it first.
 
Last edited:
cmc

cmc

Turbo Monkey
Nov 17, 2006
2,052
6
austin
urbaindk said:
I saw your post in the majesty thread....

With a little rudimentary geometry I was able to put together a spreadsheet that you can enter an approximate chain stay length, front and rear sprocket size, and wheel size that will calculate the gear inches, number of links, and actual chain stay length.

I uploaded it on google docs.

http://spreadsheets.google.com/ccc?key=r8FV6xqSjdu1WM6ea6UAbFw
Please create your own copy (ctrl-shift-S) it before playing with it. Let me know if it works. If anyone wants to check the math, that would be good too!

I used some very basic assumptions such as 1 full length = 1 inch and that the circumference of a chain ring is equal to 1/2 the number of teeth. I put in a rounding function that rounds number of chainlinks to the nearest 1/2 link.

It's very basic but it should give a good estimate. In other words, don't be a dumbass and cut your chain based on this calculation and come back and blame me later. Check it first.
Click to expand...
Glad you gave it a shot !

What do you mean by "1 full length = 1 inch" ?

Estimates/rounding etc are okay....but the goal here really has to be the exact cs length.... I mean, with any gear combination you just break your chain at the appropriate spot and you're in the ballpark.... It's within that inch or so of +1 link or -1 link that things get hairy.

I must be a dumbass because I cant figure out how to enter numbers into your calculator and make it do anything.
 
urbaindk

urbaindk

The Real Dr. Science
Jul 12, 2004
4,819
0
Sleepy Hollar
cmc said:
Glad you gave it a shot !

What do you mean by "1 full length = 1 inch" ?

Estimates/rounding etc are okay....but the goal here really has to be the exact cs length.... I mean, with any gear combination you just break your chain at the appropriate spot and you're in the ballpark.... It's within that inch or so of +1 link or -1 link that things get hairy.

I must be a dumbass because I cant figure out how to enter numbers into your calculator and make it do anything.
Click to expand...
Typo... it should be "1 full link".

Were you able to save it? I turned off editing, I think you have to save it first to your computer or own google docs account. Let me try logging out of google and open it as an anonymous user and see if I can get it to work. I repost instructions...
 
urbaindk

urbaindk

The Real Dr. Science
Jul 12, 2004
4,819
0
Sleepy Hollar
cmc said:
I must be a dumbass because I cant figure out how to enter numbers into your calculator and make it do anything.
Click to expand...
Better instructions:

If you don't have a google docs account.
click link posted above.
click File -> Export -> and select .xls
hit okay. Should open up in excel.

If you have a google docs account
click link posted above
click File -> Create a Copy

That should let you edit it. Sorry, I haven't done this before, so I'm trying to figure it out on the fly.


If that still doesn't work PM me your email addy and I'll send you the xls file.
 
Last edited:
sittingduck

sittingduck

Turbo Monkey
Jun 22, 2007
1,958
2
Oregon
Thanks. It seems to be pretty accurate. It's within .05" on all the combos I've physically measured. Chain stretch could account for some of that, since the calculator is consistently very slightly shorter than actual measurements.
Nice job!
 
urbaindk

urbaindk

The Real Dr. Science
Jul 12, 2004
4,819
0
Sleepy Hollar
sittingduck said:
Thanks. It seems to be pretty accurate. It's within .05" on all the combos I've physically measured. Chain stretch could account for some of that, since the calculator is consistently very slightly shorter than actual measurements.
Nice job!
Click to expand...
Sweet. I just sat down with a piece of paper, sketched it out, and used a little 7th grade geometry to figure it out. Glad it works in real life. If I was savvy I'd make a little gui for it with VB, but I'm lazy. Maybe another day.

Edit: I know it's tedious, but did you happen to count the links? I'm curious to know if that part of the calculation works.
 
Last edited:
sittingduck

sittingduck

Turbo Monkey
Jun 22, 2007
1,958
2
Oregon
sittingduck

sittingduck

Turbo Monkey
Jun 22, 2007
1,958
2
Oregon
I just threw a new chain on my NS, and it's now slightly UNDER 15". Just like the calculator said it should be.
I think the thing is dead on.....
 
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