# Singlespeed & Fixed Gear - for those of you who like math

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View Full Version : for those of you who like math

TimeZer0
08-13-05, 03:46 PM
I have one bike running 44/16 with 180 cranks, my new bike is running 42/14 with 165 cranks.
I thought they would feel very similar but it's like night and day- the new set up seems much easier. can anyone tell me what im pushin as far as gear inches for these?

ryan_c
08-13-05, 03:54 PM
what size tires?

165 and 180 are massively different cranks...

TimeZer0
08-13-05, 03:57 PM
700x30 on the 44/16, and 700x25 on the 42/14

bostontrevor
08-13-05, 04:12 PM
Your GI remains the same because it doesn't count crank arms, just the wheel size and gear ratio. Something like gain ratio is a more useful comparison.

http://www.sheldonbrown.com/gears/

Aeroplane
08-13-05, 06:08 PM
I have one bike running 44/16 with 180 cranks, my new bike is running 42/14 with 165 cranks.
I thought they would feel very similar but it's like night and day- the new set up seems much easier. can anyone tell me what im pushin as far as gear inches for these?

That's kind of messed up. They shouldn't feel the same, that much is for sure. Since they have the same sized wheel, you can neglect that in your calculations. So, the 44/16 gives you a ratio of 2.75, and the 42/14 has a ratio of 3.0. So, the new bike should be harder. And, the older bike has longer cranks, which should make the pedaling even easier. If you take gain ratio (gear inches w/cranks) the old = 5.1; new = 6.1. So, the new one should be way harder to pedal. And, if you take into account that most folks say a smaller ring/cog setup is harder, the new one should be even harder yet.

But you say that it's easier. My brain just melted.

r-dub
08-13-05, 07:08 PM
the tire width thing matters, though...unless you're pumping the 30's up to super high pressure there will be a lot more contact with the ground on the old bike that the new one. Less contact=less friction=easier to pedal.

queerpunk
08-13-05, 08:49 PM
hey Time, maybe the issue isn't gain ration, but muscle use... maybe the 165 offers you a pedal stroke that's better for your legs, more efficient, more muscles, blah blah something.

maybe.

queerpunk
08-13-05, 08:51 PM
also:
easier/harder isn't the same as gain ratios. easier/harder speaks to efficiency, which, like my last post hinted at, can be affected by subtle changes in geometry, and can also be affected by things like chainline and the state of your bottom bracket, hubs, and rims.

two bikes with the same gain ratios can have wildly different feels to the ride due to the efficiency, or lack thereof, of the bike--the amount of energy that's lost due to friction at various points in the bike.

Ceya
08-13-05, 10:23 PM
have one bike running 44/16 with 180 cranks, my new bike is running 42/14 with 165 cranks.

44x16 is =72.4,

42x14 is =81.0

longer cranks means you can push a larger gear, shorter cranks means push a sprint gear.

so the longer crank arms and low ratio mean you can go up hills alot easier and spin alot.

now you are pushing a harder gear and can put more power behind the gear now.

S/F<
CEYA!

TimeZer0
08-14-05, 10:17 AM
thanx for the calculations and info, makes more sense now. I knew the crank size would make a difference, guess i didn't realize the more aggressive track geometry
on my new ride would would have such an impact. It's been a blast having two totally different rides.

stevo
08-15-05, 09:55 AM
"Since they have the same sized wheel, you can neglect that in your calculations. So, the 44/16 gives you a ratio of 2.75, and the 42/14 has a ratio of 3.0. So, the new bike should be harder."

dont forget, wider tires typically have significantly higher profile. Theyre most probably NOT the same wheel size. Having said that, there's no way that the profile dif between the two will acount for the 6-or-so gear inch difference.

eddiebrannan
08-15-05, 11:14 AM
it's nothing to do with gear ratios, tire pressure or any of it. the answer is simple: new bikes are always better/easier/faster/sexier and make you more attractive to potential partners