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cervantes3773 07-18-09 05:43 PM

Gear Ratios
Not being an engineer and having never really been into cycling before, I need some help getting a handle on gear ratios. Can someone give a quick breakdown of the ratios with regard to front/rear gear size?

Thank you very much!

coldfeet 07-18-09 06:47 PM

As always Sheldon to the rescue. How we miss him.

Don't know exactly what you're after, but this chart can give various answers. Perhaps the most meaningful is what a given ratio will deliver in terms of how fast for a certain pedal cadence.

That's available to select from the 3rd option.

KevinF 07-18-09 06:52 PM

There's a good explanation here:

Edit: coldfeet beat me to it!

coldfeet 07-18-09 07:45 PM

Originally Posted by KevinF (Post 9306708)
There's a good explanation here:

Edit: coldfeet beat me to it!

Actually, I didn't. My link was just to the chart, yours is to the page of explanation, which has a link to the chart.

big chainring 07-19-09 04:32 PM

I have always measured gears in terms of gear inches. The range of gears is between 53" and 94" on my bike. When looking at Sheldons chart, calculate for gear inches. I think this is still the most used system. Am I correct?

alhedges 07-19-09 08:16 PM

Most people I know use gear inches.

It's not that gear inches measure anything particularly useful, but they do give you a nice range with a lot of discrete numbers, which is fairly easy to understand.

My bike's range, in gear inches, is something like 22-100. Dividing my 27 gears among the 78 available inches gives me lots of whole numbers I can use to describe my gears, without requiring the use of decimals.

In gain ratios, my bike's range is 1.7 to 7.5, approximately. I still have the same 27 gears, but now I'm dividing them up among 5.8 spaces (rather than 78). Although my bike travels the same distance in any system, for me it is more intuitive to think of some of my lower gears as being 26, 30, 31, 35, 36, etc. gear inches, as opposed to having gain ratios of 2.0, 2.3, 2.4, 2.7, 2.8.

These numbers are arbitrary, I suppose, and if I grew up using gain ratios, maybe I would prefer it. But most people seem to be used to gear inches...

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