The Friday Cyclotouriste

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Archive for the ‘gear ratios’ tag

Gear Gallery……Freewheels and Gear Ratios

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I once avoided anything having to do with gear ratios as the subject would make my eyes glaze over, but they’re obviously really important. The late Sheldon Brown — expert on everything bicycle related — created a simple and useful gear calculator which helped reduce my fear of the arcane subject.

My Guerciotti originally had a rear cluster of cogs ranging from 13-23 teeth, as seen on the freewheel on the right, which is a good set-up for racing on mostly flat or rolling terrain.

But here’s the problem: this gear range — coupled with 42t and 52t chain rings in front — is horribly suited for Marin County’s mountainous terrain (remember: the more teeth, the bigger the cog, and the easier it is to pedal. For the front chain rings — the opposite is true).

The solution: ditch this set-up and replace it with a cluster with a 25t as the largest cog. This worked much better, but I still yearned to spin an easier gear up Bolinas ridge and other tough climbs. I discovered that some 6-speed freewheels were made with a 28t cog, which seemed just perfect and wouldn’t require a special long-cage rear derailer (necessary for rear cogs above 28t).

A Suntour freewheel with a 28t cog is pictured on the left.

I can’t wait to install it!

Technical Note: According to Sheldon’s calculator, with the new Suntour freewheel my drive wheel has an equivalent diameter of 40.1 inches (i.e. gear inches) compared to 48.9 inches using the original 23t freewheel, resulting in about a 20% improvement. Still, the low gear of a typical mountain or touring bike is another 50% or so lower, at around  20-25 gear inches.

Written by fridaycyclotouriste

January 28th, 2010 at 11:29 pm