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My bike has several gears labelled one to six. Do these numbers relate specifically to a certain standard? In other words, would a bike set to say gear four on one bike, perform in the same way as another different bike set to the same gear?

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Generally they're numbered such that #1 is the lowest gear. Other than that there's no rule. Even two bikes with an identical number of gears could have wildly different gear ratios. –  Daniel R Hicks Dec 4 '11 at 22:01
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1 Answer

up vote 9 down vote accepted

No.

The full gearing ratio of the bike (from your foot to the tire contact patch) is determined by four factors: the crank length, the chainring diameter, the cog diameter and the wheel diameter. Since these components can be changed independently, it is impossible to develop a uniform numbering system for a single component ("uniform" in this case means getting the same full gearing ratio from the same gear numbers selected for the chainring and for the cog).

I.e. even if you standardize the "front gear number to chainring diameter" and "rear gear number to cog diameter" relationships, two bikes with different wheel diameters will still perform significantly differently even when the same gear numbers are selected on both of them.

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