Bike Forums - View Single Post - ''Double shift'' with a compact? huh?

07-16-13 | 10:33 AM

#2

merlinextraligh

pan y agua

Joined: Aug 2005

Posts: 31,812

Likes: 1,233

From: Jacksonville

Bikes: Willier Zero 7; Merlin Extralight; Calfee Dragonfly tandem, Calfee Adventure tandem; Cervelo P2; Motebecane Ti Fly 29er; Motebecanne Phantom Cross; Schwinn Paramount Track bike

The point is to ameliorate the big jump in gear ratios when you make the front switch..

For example, if you're in the 50/21 combination, and you shift just the front chainring, at 85 rpm, your speed is going to drop from 16mph to 11 mph.

In most cases, that's a bigger jump than you want; and your speed will drop dramatically, or your cadence will have to jump dramatically.

If you shift 2 cogs down on the back at the same time you go to the 34 in the front, you end up in the 34/16, and you get a smaller change in gear ratio, and s your speed only falls to 14mph.

You can play with this to figure out your desired shifting pattern:

http://www.gear-calculator.com/#

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Last edited by merlinextraligh; 07-16-13 at 10:36 AM.

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