Explain to me, gear inches
03-21-07 | 02:44 PM
#8
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From: GA
Originally Posted by cphfxt
How else to make a schematic comparison of ,say 44x17 and 50x19. Which is bigger? How would you measure if not in distance travelled?
well if the wheel size is the same it's easy
2.58 vs 2.63
03-21-07 | 02:45 PM
#9
domestique
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From: off the back
Originally Posted by William Karsten
Perhaps I'm getting old an onerous, like 165.
But really, why do gear inches matter to people? I can't for the life of me understand why it @#$@# matters. It seems people obsess over it. I started 42x16. It got easy. I bumped up once to 44x16. Things weren't hard. I built some stamina, some speed, got comfy and went 48x15. Which seems plenty. How would gear inches play into this? It seems to me that it really superflous information.
Or, I'm the last man out of the cave.
But really, why do gear inches matter to people? I can't for the life of me understand why it @#$@# matters. It seems people obsess over it. I started 42x16. It got easy. I bumped up once to 44x16. Things weren't hard. I built some stamina, some speed, got comfy and went 48x15. Which seems plenty. How would gear inches play into this? It seems to me that it really superflous information.
Or, I'm the last man out of the cave.
03-21-07 | 02:46 PM
#10
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Its a way of expressing how easy or hard a gear is. Since there are many equivalent gears, for example a 51/17 is exactly the same as a 48/16, its easier to talk about gear inches, which is the number of inches the bike travels with one revolution of the pedals, than it is to talk about specific CR/cog combinations.
In general, a 70 inch gear is a pretty easy around town gear for the flats. The 42/16 gear you started with is about 70 inches. Track racers usually ride something in the 88-92 inch range. Your 48/15 is about 86 inches, so you are getting up there with the track racers.
Easy to calculate, Cr teeth divided by cog teeth times 27 gives you gear inches.
In general, a 70 inch gear is a pretty easy around town gear for the flats. The 42/16 gear you started with is about 70 inches. Track racers usually ride something in the 88-92 inch range. Your 48/15 is about 86 inches, so you are getting up there with the track racers.
Easy to calculate, Cr teeth divided by cog teeth times 27 gives you gear inches.
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Il faut de l'audace, encore de l'audace, toujours de l'audace
1980 3Rensho-- 1975 Raleigh Sprite 3spd
1990s Raleigh M20 MTB--2007 Windsor Hour (track)
1988 Ducati 750 F1
03-21-07 | 02:46 PM
#11
lunatic fringe
Joined: Aug 2005
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From: Miles from Nowhere, Columbia County, OR
Bikes: 1980 Schwinn World Sport, 1982 Schwinn Super Le Tour, 1984 (?) Univega Single Speed/Fixed conversion, Kogswell G58 fixed gear, 1987 Schwinn Super Sport
Originally Posted by moe sizlack
it's another way for people to be vague.
03-21-07 | 02:49 PM
#12
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Originally Posted by William Karsten
I started 42x16. It got easy. I bumped up once to 44x16. Things weren't hard. I built some stamina, some speed, got comfy and went 48x15.
and some will say that gear inches is useless without taking crank length into account. hence sheldon's gain ratios.
03-21-07 | 02:49 PM
#14
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From: GA
Originally Posted by Dogbait
There's nothing vague about a system that measures exactly how far down the road your particular set-up will carry your butt for each turn of the crank.
03-21-07 | 02:50 PM
#15
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From: under bridge in cardboard box
except gear inches doesnt equal distance traveled per crank revolution
circumference= Pi * diameter
gear inches = gear ratio * wheel diameter
actual distance traveled per crank revolution is gear ratio times circumference
circumference= Pi * diameter
gear inches = gear ratio * wheel diameter
actual distance traveled per crank revolution is gear ratio times circumference
03-21-07 | 02:54 PM
#17
blah
Joined: Oct 2005
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From: Oakland, CA
read this: https://www.sheldonbrown.com/gain.html
03-21-07 | 02:54 PM
#18
nothing but a gnab gib
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From: Rock City
Bikes: The Heart of Gold starship bicycle
Originally Posted by Dogbait
There's nothing vague about a system that measures exactly how far down the road your particular set-up will carry your butt for each turn of the crank.
03-21-07 | 03:06 PM
#19
jack of one or two trades
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From: Suburbia, CT
Bikes: Old-ass gearie hardtail MTB, fix-converted Centurion LeMans commuter, SS hardtail monster MTB
Originally Posted by William Karsten
But really, why do gear inches matter to people?
I agree with you for on-road stuff though, not many folks go between 650c, 650B, and 700c at all.
03-21-07 | 03:53 PM
#21
Originally Posted by bonechilling
Totally OT, but you know that you spelled "Szyslak" wrong,
right?
right?
Sleestaks
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This is Africa, 1943. War spits out its violence overhead and the sandy graveyard swallows it up. Her name is King Nine, B-25, medium bomber, Twelfth Air Force. On a hot, still morning she took off from Tunisia to bomb the southern tip of Italy. An errant piece of flak tore a hole in a wing tank and, like a wounded bird, this is where she landed, not to return on this day, or any other day.
This is Africa, 1943. War spits out its violence overhead and the sandy graveyard swallows it up. Her name is King Nine, B-25, medium bomber, Twelfth Air Force. On a hot, still morning she took off from Tunisia to bomb the southern tip of Italy. An errant piece of flak tore a hole in a wing tank and, like a wounded bird, this is where she landed, not to return on this day, or any other day.
03-21-07 | 04:02 PM
#22
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Originally Posted by Aeroplane
One valid reason I can think of is going between offroad 26" and 29" wheeled bikes. In order to keep your gearing consistent, you figure out the gear inches and keep that the same.
I agree with you for on-road stuff though, not many folks go between 650c, 650B, and 700c at all.
I agree with you for on-road stuff though, not many folks go between 650c, 650B, and 700c at all.
03-21-07 | 04:18 PM
#24
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Originally Posted by San Rensho
Since there are many equivalent gears, for example a 51/17 is exactly the same as a 48/16,
can someone sum up the advantage/disadvantage (if any) of 2 different combinations that have the same gear inches?
