A gear train is a series of gear pairs in diferent axes. The gear ratio of each pair is obtained dividing one gear number of teeth by the other's.

When you put more than two pairs you have to multiply each pair ratio.

And if each pair ratio is the same you can use

where n is the number of pairs.

For a example, check the model "Gear train" in phunbox. It has a 13/24 = .5417 ratio in each pair, and (13/24)^3 = .1589 in all the gear train.

http://www.phunland.com/phunbox/details/21047

--Ochoadavid 16:17, 6 May 2009 (UTC)