[crazybeach]

So I found a magic gear ratio on my 2002 Gary Fisher Supercaliber, it is 30x19, which is too small for my liking. My question is if I bring the front ring to 31 and drop the rear to 18 I won't have to change my chain length, right? Sorry if seems like a dumb question but any help is appreciated!

 

[fishcreek]

31x18 will be hair tighter. If you have a little slack right now it MIGHT work.

 

[Saul Lumikko]

For very small adjustments you can file the dropouts and/or axle.

Adding and deducting teeth to chainrings and cogs has a different effect because the relative change in diameter and amount of chain wrap varies. It's fairly complex but thankfully there are calculators to make toying with numbers easier.

 

[alixta]

If you know the chainstay length then you can calculate how close each chainring/cog combo will be to *magic*. Park tool has the formula on their website, I'll try to dig out my spreadsheet.

 

[Thor29]

31 teeth chainrings are gonna be hard to find. Surly makes one for a 94mm BCD crank but not for the standard 104mm BCD.