Highpath Engineering : Cycle gear ratio chart : (wheel radius / crank length) = 2.9

Gear ratio chart

when (wheel radius / crank length) = 2.9

This chart shows gear ratios for different chainrings and sprockets on a cycle where (wheel radius / crank length) equals 2.9.

A gear ratio specifies how hard it is to push a particular gear. A ratio of 5 means that your cycle moves 5 metres along the ground for every metre you move the pedals, or 5 inches for every inch, or 5km for every km. Smaller ratios are easier to push and higher ones make you go faster.

              gear ratio   =   wheel radius  ×    no. of chainring teeth  
                               crank length     no. of rear sprocket teeth

		chainring (teeth)
		20	22	24	26	28	30	32	34	36	38	40	42	44	46	48	50	52
rear sprocket (teeth)	11	5.3	5.8	6.3	6.9	7.4	(7.9)	(8.4)	(9.0)	(9.5)	(10.0)	(10.5)	(11.1)	(11.6)	(12.1)	(12.7)	(13.2)	(13.7)
	12	4.8	5.3	5.8	6.3	6.8	7.3	(7.7)	(8.2)	(8.7)	(9.2)	(9.7)	(10.2)	(10.6)	(11.1)	(11.6)	(12.1)	(12.6)
	13	4.5	4.9	5.4	5.8	6.2	6.7	7.1	(7.6)	(8.0)	(8.5)	(8.9)	(9.4)	(9.8)	(10.3)	(10.7)	(11.2)	(11.6)
	14	4.1	4.6	5.0	5.4	5.8	6.2	6.6	7.0	7.5	(7.9)	(8.3)	(8.7)	(9.1)	(9.5)	(9.9)	(10.4)	(10.8)
	15	3.9	4.3	4.6	5.0	5.4	5.8	6.2	6.6	7.0	7.3	(7.7)	(8.1)	(8.5)	(8.9)	(9.3)	(9.7)	(10.1)
	16	3.6	4.0	4.4	4.7	5.1	5.4	5.8	6.2	6.5	6.9	7.3	(7.6)	(8.0)	(8.3)	(8.7)	(9.1)	(9.4)
	17	3.4	3.8	4.1	4.4	4.8	5.1	5.5	5.8	6.1	6.5	6.8	7.2	7.5	(7.8)	(8.2)	(8.5)	(8.9)
	18	3.2	3.5	3.9	4.2	4.5	4.8	5.2	5.5	5.8	6.1	6.4	6.8	7.1	7.4	(7.7)	(8.1)	(8.4)
	19	3.1	3.4	3.7	4.0	4.3	4.6	4.9	5.2	5.5	5.8	6.1	6.4	6.7	7.0	7.3	(7.6)	(7.9)
	20	2.9	3.2	3.5	3.8	4.1	4.4	4.6	4.9	5.2	5.5	5.8	6.1	6.4	6.7	7.0	7.3	7.5
	21	2.8	3.0	3.3	3.6	3.9	4.1	4.4	4.7	5.0	5.2	5.5	5.8	6.1	6.4	6.6	6.9	7.2
	22	2.6	2.9	3.2	3.4	3.7	4.0	4.2	4.5	4.7	5.0	5.3	5.5	5.8	6.1	6.3	6.6	6.9
	23	2.5	2.8	3.0	3.3	3.5	3.8	4.0	4.3	4.5	4.8	5.0	5.3	5.5	5.8	6.1	6.3	6.6
	24	2.4	2.7	2.9	3.1	3.4	3.6	3.9	4.1	4.4	4.6	4.8	5.1	5.3	5.6	5.8	6.0	6.3
	25	2.3	2.6	2.8	3.0	3.2	3.5	3.7	3.9	4.2	4.4	4.6	4.9	5.1	5.3	5.6	5.8	6.0
	26	2.2	2.5	2.7	2.9	3.1	3.3	3.6	3.8	4.0	4.2	4.5	4.7	4.9	5.1	5.4	5.6	5.8
	28	2.1	2.3	2.5	2.7	2.9	3.1	3.3	3.5	3.7	3.9	4.1	4.4	4.6	4.8	5.0	5.2	5.4
	30	1.9	2.1	2.3	2.5	2.7	2.9	3.1	3.3	3.5	3.7	3.9	4.1	4.3	4.4	4.6	4.8	5.0
	32	1.8	2.0	2.2	2.4	2.5	2.7	2.9	3.1	3.3	3.4	3.6	3.8	4.0	4.2	4.4	4.5	4.7
	34	1.7	1.9	2.0	2.2	2.4	2.6	2.7	2.9	3.1	3.2	3.4	3.6	3.8	3.9	4.1	4.3	4.4

Choosing your gears

Many cyclists like their 'normal' gear to have a gain of about 5.0, and an overall range from 2.5 to 7.0.
Gear ratios under 0.8 are too low for bicycles as it's difficult to balance at such slow speeds.
Gear ratios over 7.5 are too high for general use on bicycles (7.5 has been used to break World records!).

For derailleur gears:

Choose chainrings and sprockets that give your preferred top and bottom gears and a sensible spread inbetween.
Choose similar percentage jumps between your rear sprockets, not equal numbers of teeth.

For hub gears:

Choose a chainring and sprocket that give your preferred middle gear. Multiply this by the high and low ratios for your hub in order to find your top and bottom gears.

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