Ratio Query - Sorry don't undertand it all so any help greatly appreciated!

[nickyboy]

I don't think you're accounting for wheel size in that. For the same wheel size, then yes it's a rough comparison but you can't compare different bikes and wheel and tyre sizes that way.

Wheel diameter(inches)x(chainwheel/cog) is gear inches.

I think it's the use of inches that I object to. It's redolent of an era of salad cream, flasks of tea and tartan travel rugs

 

[Crackle]

I think it's the use of inches that I object to. It's redolent of an era of salad cream, flasks of tea and tartan travel rugs

Rhyl smells heavily of that era to me.

I'm sure you can use gear cm's if you like. Less furry dice, magnetic compass and more car DVD player and tablet.

Although I'm reminded by a quick memory refresh at Sheldon's page that none of that takes into account crank length!

 

[Dogtrousers]

All this talk of gear inches....makes my head hurt. Seems so archaic a system

I'm relatively new to cycling. All I work out in my head is the Teeth on Front Ring / Teeth on Back Sprocket as a ratio. This ratio accurately identifies how many times my back wheel rotates per turn of the cranks, no?

So 50/25 is the same as 34/17 for example.

Yebbut it doesn't work if you have two bikes and one of 'em has different sized wheels.

But if you always ride standard 622mm rims with the same sized tyres then the ratio alone will do fine.

If you don't want to smell so much of salad cream you could use "developpement" in cm (how far you go with each turn of the pedals). Or Sheldon Brown came up with a whacky thing that also takes into account crank length. http://www.sheldonbrown.com/gain.html

I'm an ardent metricist, but I use "gear inches" for gears. It's just a number.

 

[nickyboy]

I don't think you're accounting for wheel size in that. For the same wheel size, then yes it's a rough comparison but you can't compare different bikes and wheel and tyre sizes that way.

Wheel diameter(inches)x(chainwheel/cog) is gear inches.

If you ever see me on a Brompton you have my permission to shoot me