Gear Inches/Ratio

[migrantwing]

I've always wondered what constitutes a close gear inch or ratio, and how do you work ratio's out?

For instance:

50/ 21 = 62.6
34/ 14 = 63.9 or
34/ 15= 59.7.

I understand the basics but, physically speaking, how close or far away would these compare in relation to feel? At what point would I feel or notice a physical difference when pedaling? Are we talking within 1 gear inch or 5 or even 0.5 to feel a difference?

How does this equate to ratio?

TIA

 

[Dogtrousers]

Depends, really.

There are times when I'm toiling up a hill when I yearn for a gear that's half an inch lower. Hell, 3/8" a 1/16" ... anything. I've even considered stopping and letting my back tyre down to make the wheel a tad smaller

On the other hand, once you're over 100" they're all just "high" to me.

 

[migrantwing]

[QUOTE 3862927, member: 9609"]It is a rather curious figure of Wheel Diameter multiplied by the gear ratio.
52 chain ring feeding a 18 sprocket with a 26.7" diameter wheel
(52/18)*26.7 = 77.13 gear inches

the feel between gears is very much a percentage thing. 7% is a very close gear - 15% is a very noticable change.

changing between 52T chainring and 39T Chainring is 33.3% change
24T sprocket to a 21T sprocket = 14.2% which is fine for a tourer.
14T sprockt to a 13T sprocket = 7.7 % which is what flatlanders like.

Your figures 63.9 to 59.7 = 7%

gear inches is good for comparing different bikes - with the same bike just compare the percentage diff between srockets[/QUOTE]

Great explanation. Thank you, @User9609

 

[Ihatehills]

Thanks @User9609
I'd never heard of gear inches before but have been meaning to work out the gear differences between my old bike and the new one.now I can do it properly, I'm sure id have done the same thing but expressed in a much more complicated manner :-)

 

[mjr]

Now I'm used to 36% steps on the roadster, the 10% steps on the folding bike seem so small that I often change two at a time!

 

[Racing roadkill]

Put s Brompton rear wheel on your road bike, a 34T up front and a 34T big sprocket, you'll be flying up vertical cliffs in no time.

 

[ColinJ]

I make things easier for myself by thinking of a nominal 27" wheel, and I round the inches figure to the nearest whole number. That gives numbers which are near enough for my purposes.

 

[Cyphrex]

I truly find the gear ratio/inches knowledge-base very enlightening to study when I'm not on the bicycle, however once I'm in the saddle my only focus is to keep a steady cadence (which is made harder by the larger ratios of MTB triples), keep the shiny side of the cycle up and avoid hazards along the way. I think knowing the ratio helps me more to know the mechanical advantages I can gain out of different ratios that are available. Someone's tip I read to use lower gear ratios during headwinds has helped as well as GCN's tips on changing gears like a pro.

 

[Smurfy]

[QUOTE 3863353, member: 9609"]Sheldon Brown does an online calculator LINK
http://www.sheldonbrown.com/gears/
He has a few other methods of comparison to consider too.[/QUOTE]
I use the Sheldon Brown one, but this one is good for different reasons.
http://www.gear-calculator.com/
Just drag the chainrings and sprockets with your mouse.