Gear range of a drivetrain

The gear range of a drivetrain is its highest gear divided by its lowest. The highest gear is the largest chainring on the smallest cog; the lowest is the smallest chainring on the largest cog. So range = (largest chainring ÷ smallest cog) ÷ (smallest chainring ÷ largest cog), and it is usually written as a percentage: a top gear 4.2 times the bottom gear = a range of 420 %.

With one chainring the chainring cancels out, and the range is simply largest cog ÷ smallest cog. That is why a single ring needs a very wide cassette to match a double: the double multiplies the cassette's range by the ratio of its two rings.

Range is a ratio, so it does not say where the gears sit. Two drivetrains with the same range can differ at both ends: put a smaller chainring on the same cassette and every gear, lowest and highest, drops by the same share. The calculator therefore reports the lowest and highest gear of each drivetrain in gear inches, and the change at each end.

The range also says nothing about the steps between gears. A wider range on the same number of cogs means bigger jumps from one cog to the next, and on a double or triple some combinations repeat, so the number of really different gears is smaller than chainrings × cogs.

Chart: gear range of a single chainring, by largest and smallest cog

Each cell is the range for the largest cog in its row and the smallest cog in its column. With one chainring its size does not matter.

	A: smallest cog
A: largest cog	9	10	11	12
28	311 %	280 %	255 %	233 %
30	333 %	300 %	273 %	250 %
32	356 %	320 %	291 %	267 %
34	378 %	340 %	309 %	283 %
36	400 %	360 %	327 %	300 %
40	444 %	400 %	364 %	333 %
42	467 %	420 %	382 %	350 %
44	489 %	440 %	400 %	367 %
46	511 %	460 %	418 %	383 %
50	556 %	500 %	455 %	417 %
51	567 %	510 %	464 %	425 %
52	578 %	520 %	473 %	433 %

Work out your own numbers: Bike gear range calculator

Chart: gear range of a road double, by largest cog and small chainring

Each cell is the range for the largest cog in its row and the small chainring in its column. Large chainring = 50 teeth; smallest cog = 11 teeth.

	A: smallest chainring
A: largest cog	34	36	39
25	334 %	316 %	291 %
28	374 %	354 %	326 %
30	401 %	379 %	350 %
32	428 %	404 %	373 %
34	455 %	429 %	396 %
36	481 %	455 %	420 %

Work out your own numbers: Bike gear range calculator

Chart: lowest gear of a road double in gear inches, by largest cog and small chainring

Each cell is the lowest gear, in gear inches, for the largest cog in its row and the small chainring in its column. Wheel = a 28-622 tire (700 × 28C).

	A: smallest chainring
A: largest cog	30	33	34	36	39
25	32.0 in	35.2 in	36.3 in	38.4 in	41.6 in
28	28.6 in	31.5 in	32.4 in	34.3 in	37.2 in
30	26.7 in	29.4 in	30.3 in	32.0 in	34.7 in
32	25.0 in	27.5 in	28.4 in	30.0 in	32.5 in
34	23.6 in	25.9 in	26.7 in	28.3 in	30.6 in
36	22.2 in	24.5 in	25.2 in	26.7 in	28.9 in

Work out your own numbers: Bike gear range calculator

Used by

• Bike gear range calculatorGear range and end gears of two drivetrains, side by side.

Sources

• Wikipedia: Bicycle gearing
• Sheldon Brown: Gain ratios