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Gear Ratios(5 posts)

Gear Ratios8cht
Feb 19, 2003 3:36 PM
I've been using a 42T chainring with a 16T cog while commuting to work here in the Washington, DC area (fairly flat with some hills). A mechanic at a bike shop in DC that supports couriers stated that I need to be running a 3:1 ratio (apparently all the couriers run this mix). That would be a 48/16T. That's quite a jump from the 42/16T. What are your opinions on the 3:1 dictum and what is everyone else generally using? Thanks.
re: Gear Ratiosvelo_junkie
Feb 19, 2003 3:47 PM
You should have the gearing that suits you, not the messengers. I'm running 42/16 here in San Luis Obispo. It depends on how fast you wanna spin and how fast you want to ride. If you like 42/16 stick with it. Or experiment, but don't just go with what someone dictates. What works for some doesn't work for others. For example, my roomate runs a 52/17 (3.05) Which I can't handle around here.
Hope this helps.

velo_junkie
It's totally up to you...biknben
Feb 19, 2003 4:12 PM
I run a mix of gears between 42/15-17 for my commute. It's mostly flat with some rises equal to big highway overpasses.

I let cadence determine my gear size. I choose a gear that will keep me in a certain range. I don't want to be forced to grind gears to get up a rise. OTOH, I don't want to be spinning like a fool on the down side. I pick a gear that is acceptable for both. Actually, I pick the gear I want to climb in. I brake on the downhill if I can't spin fast enough.

What the messangers are riding shouldn't impact you at all.
2.5:1 is the traditional starting place ...Humma Hah
Feb 19, 2003 4:19 PM
... that is time-tested for 120 years or so as the all-around singlespeed/fixed mixed-riding road gear, with 2:1 being the starting point for cyclocross and other off-road applications. The conventional wisdom is to start at 2.5:1 for road riding, and adjust as you see fit.

But I can see 3:1 for DC. I've got a 46:16 combo for the cruiser that can manage a credible climb on a long 6% grade, so slightly higher gearing on a light bike with no big hills is probably workable, if you spend a lot of time going fast. If you need to do a lot of slow work picking thru crowds and other obstacles, you'll not have much of a spin going, and it will reduce your acceleration if you do a lot of stop-and-go.

Most riders have an assortment of rear cogs on hand and swap them to see what works best, but the great beauty of singlespeed and fixed is the realization that whatever gear you happen to have, within reason, will get the job done.
Calculate before you changebigrider
Feb 20, 2003 5:24 AM
Use the interactive tools at http://www.analyticcycling.com/ to determine your cadence from speed or speed from cadence given your chainring/cog combo. Climb a hill and determine the speed you want to go and then figure out your cadence with your combo. It is a good starting point rather than going out and buying a bunch of cogs and realize you can't tick over the pedals up the steepest hill in your commute or you are pedaling a 110 cadence on the flats going 18mph.

Hummah is right about the 2.5 to 1 as a starting point. If it is flat a 3 to 1 is great.