|gear ratio question||ballbite|
Jun 1, 2003 4:56 AM
|At least once a year I like to do some mountainous rides in New Hampshire. These usually involve stretches of up to 5 miles at a 9% grade. My older road bike has a triple with the lowest gear ratio being 30/25. I found I had to use this gear on a lot of the climb because of its length.
My new road bike has a double. I had it equipped with a 27 tooth large ring in the back so my lowest gear ratio is 39/27.
Since I don't have long stretches of 9% grade where I live, I don't know how this ratio is going to be if I try those New Hampshire rides again. Any ideas if this is going to be low enough for me to do these climbs?
|Try this:||Spoke Wrench|
Jun 1, 2003 5:19 AM
|Gear inches equals chainring teeth divided by rear cog teeth multiplyed by 27. That gives you a number that you can compare and it's a common bike term so most bike mechanics will know what you are talking about.
Your old bike had a 32 inch low gear. New bike has 38 inch low gear. That's quite a bit of difference. The cheap, dirty solution is to install a mountain bike cassette, rear derailleur and new longer chain. That can give you a low gear as low as 30 gear inches, will work fine with the shifters you have, and you can take it off after your tour is finished.
|Swapping the chainring would also work [nm]||bent_spoke|
Jun 1, 2003 7:43 AM
|38 is usually the smallest you can go...||CurtSD|
Jun 2, 2003 7:30 AM
|and that won't be enough. You could swap in a different crank, like a 110 bcd TA Zephyr (http://www.peterwhitecycles.com/zephyr.asp) and put something like 50/36 rings on it, but if you're doing that you might as well just go back to the triple.|
|No, it won't be||Alexx|
Jun 1, 2003 8:53 AM
|30/25 = 32.4 gear inches
39/27 = 39.0 gear inches.
You would need a 33 tooth cog to give you nearly the same gear with a 30 tooth ring. The other idea of switching rings is silly, since most road bikes can't take smaller than a 39 tooth small ring. Chances are pretty good that the 27 tooth is the biggest you can use with a short cage rear derailleur.
Jun 1, 2003 9:11 AM
|If you really needed the 30x25 then you are going to need a 12-32 cassette and a MTB rear deraileur to be able to get nearly the same gears. Even that is not quite as low as you had before, but your new bike is probally a little lighter and you should be able to make it up the hill in 39x32.|
|re: gear ratio question||firstrax|
Jun 1, 2003 10:41 AM
|Exactly where in NH?|
|re: gear ratio question||ballbite|
Jun 1, 2003 5:28 PM
|Kancamagus highway and from North Conway up to Pinkham Notch are a couple examples of 9% climbs I've ridden.|
|you can get a 38 tooth ring; will help a little nm||DougSloan|
Jun 2, 2003 6:32 AM