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Gear inches

Old 09-24-21, 05:51 PM
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Mike Disco
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Gear inches

I've been looking for a chart on gear inches. How to determine what's the best gear inches and how many patches do I have on my fixedgear. 🌀
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Old 09-24-21, 06:30 PM
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sovende
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Go to Sheldonbrown.com for gear inch info.
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Old 09-24-21, 06:35 PM
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Sheldon or here: https://www.bikecalc.com/skid_patch_calculator
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Old 09-24-21, 06:39 PM
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I like Sheldons online gear calculator also but K Gear Software is a windows program and was written by KINETICS recumbent shop. They even have the Schlumpf gears included.
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Old 09-24-21, 08:54 PM
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Use a 17T or a 19T cog with any chainring and you'll always have 17 or 19 skid patches!

Gear inch charts do a good enough job, but if you have 650b wheels they usually don't list many tire sizes.

If you learn the gear-inch formula and know the actual wheel + tire diameter, you don't need a chart. More accurate, too.

To get the actual diameter: Rim Diameter + (Tire Width X 2) X .03937 = Actual Diameter (in inches)
700c = 622 Rim Diameter
650b = 584 Rim Diameter
26" = 559 Rim Diameter
To get gear inches: Actual Diameter X Chainring Teeth / Sprocket Teeth = Gear Inches

Last edited by Rolla; 09-24-21 at 08:58 PM.
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Old 10-02-21, 08:34 PM
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Originally Posted by oldbobcat View Post
Don't forget. To get gear inches you have to convert the millimeters to inches. 1 inch equals 25-POINT-4 mm.
FTFY Just in case.

Also, gear inches has nothing directly to do with how many skid patches you get. The same gear combo on any tire or wheel size will yield exactly the same skid spots locations.

Last edited by DiabloScott; 10-02-21 at 08:40 PM.
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Old 10-03-21, 07:47 PM
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Traditionally, racing cyclists started winter/spring riding with 70 inches (equivalent direct-drive wheel diameter) and adjusted up or down as needed. Usually, changing the rear cog by one tooth is enough to notice and matter.

That 70 inches is for racking up the winter/spring miles on the road. For stunt riding, the usual choice may be lower, perhaps 63 inches. I wouldn't actually know, but maybe somebody here does. For in-town commuting or errands, with lots of stops at lights etc and often carrying a load, I do know that 67-68 inches makes more sense than 70 inches. Pick a gear, build it up and ride it, ask yourself after a week or two if you want a higher or lower gear more often, and go up or down a cog tooth accordingly. Then it will really be your bike.
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Old 10-04-21, 04:32 PM
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If you have a prime number tooth count on either the chainring or the sprocket, the number of skid patches will be equal to the number of teeth on the rear sprocket.
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Old 10-04-21, 09:25 PM
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I'm a middle-aged fat slow guy. Also, though I've ridden fixed gear and singlespeed both on and off-road, and I raced track as a junior, I actively dislike fixed and singlespeed bikes these days, and will likely never own another one.

All that said:

On my sport-touring / commuting bike, on 700cx23s, I spend most of my time, when not climbing or descending hills, in one of three gears: 42x18, 45x18, and 42x16. Or, 61.28, 65.75, and 69.17 gear inches respectively. My #1 flatland gear is the 45x18 (65.75"). A significant headwind or a long false flat will see me in the 42-or-45x20, but my 18T cog sees the most use.

All of this is on a 45/42/30x14-16-18-20-23-26 half-step triple, but I hope it might be useful to your situation.

--Shannon
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