[urbaindk]

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.

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.

 

[cmc]

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.

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]

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.

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]

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

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.

 

[sittingduck]

Very cool!

It's working for me using the Create a Copy method.

 

[urbaindk]

Awesome! I just emailed you a copy as well.

 

[sittingduck]

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]

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!

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.

 

[sittingduck]

I checked the links on my Majesty and it was right.

 

[sittingduck]

http://software.bareknucklebrigade.com/rabbit.applet.html
This is a nice gearing calculator.
Between this, and the chainstay calculator, figuring out the ideal gearing for that new build should be a cinch!

 

[Cru Jones]

Bikeguide has a similar chart for ratio vs chain length (all 20"). I'm too lazy to check it, but I wonder if it works out the same as your calculator?

http://www.bikeguide.org/guides/drive/gearchart.php

 

[sittingduck]

Bikeguide has a similar chart for ratio vs chain length (all 20"). I'm too lazy to check it, but I wonder if it works out the same as your calculator?

http://www.bikeguide.org/guides/drive/gearchart.php

It's off by about 1/4"
At least they put a disclamer on it!

Gear Ratio Vs. Chain Length
All is based on a new chain, and is approximate (in other words, if its wrong.. sorry).

 

[sittingduck]

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.....

 

[nwd_26]

Bumping with the calculator I use....

It's proven very accurate, I slotted and chopped my drops based on it and it's perfect.

 

[sittingduck]

Bumping with the calculator I use....

It's proven very accurate, I slotted and chopped my drops based on it and it's perfect.

Very nice!

 

[martin]

Nice man, thanks.