The values come from the same formula as our crank length calculator. The classic chart is the one bike shops have used for years, in 2.5 mm steps. Today’s trend takes about 5 mm off that number so you pedal with a more open hip angle, a change many pros have made in recent years. For mountain and triathlon we take off another 2.5 mm: on the mountain bike, to strike fewer pedals on rocks and roots; on the triathlon bike, to open the hip angle with your torso stretched flat.
Crank length by inseam and type of bike
| Inseam | Classic chart | Road, gravel and hybrid | Mountain | Triathlon | Reasonable range (road) |
|---|---|---|---|---|---|
| 26.0 in (66.0 cm) | 165 mm | 160 mm | 157.5 mm | 157.5 mm | 157.5-165 mm |
| 26.5 in (67.3 cm) | 165 mm | 160 mm | 157.5 mm | 157.5 mm | 157.5-165 mm |
| 27.0 in (68.6 cm) | 165 mm | 160 mm | 157.5 mm | 157.5 mm | 157.5-165 mm |
| 27.5 in (69.9 cm) | 165 mm | 160 mm | 157.5 mm | 157.5 mm | 157.5-165 mm |
| 28.0 in (71.1 cm) | 165 mm | 160 mm | 157.5 mm | 157.5 mm | 157.5-165 mm |
| 28.5 in (72.4 cm) | 165 mm | 160 mm | 157.5 mm | 157.5 mm | 157.5-165 mm |
| 29.0 in (73.7 cm) | 165 mm | 160 mm | 157.5 mm | 157.5 mm | 157.5-165 mm |
| 29.5 in (74.9 cm) | 170 mm | 165 mm | 162.5 mm | 162.5 mm | 162.5-170 mm |
| 30.0 in (76.2 cm) | 170 mm | 165 mm | 162.5 mm | 162.5 mm | 162.5-170 mm |
| 30.5 in (77.5 cm) | 170 mm | 165 mm | 162.5 mm | 162.5 mm | 162.5-170 mm |
| 31.0 in (78.7 cm) | 170 mm | 165 mm | 162.5 mm | 162.5 mm | 162.5-170 mm |
| 31.5 in (80.0 cm) | 172.5 mm | 167.5 mm | 165 mm | 165 mm | 165-172.5 mm |
| 32.0 in (81.3 cm) | 172.5 mm | 167.5 mm | 165 mm | 165 mm | 165-172.5 mm |
| 32.5 in (82.6 cm) | 172.5 mm | 167.5 mm | 165 mm | 165 mm | 165-172.5 mm |
| 33.0 in (83.8 cm) | 172.5 mm | 167.5 mm | 165 mm | 165 mm | 165-172.5 mm |
| 33.5 in (85.1 cm) | 172.5 mm | 167.5 mm | 165 mm | 165 mm | 165-172.5 mm |
| 34.0 in (86.4 cm) | 175 mm | 170 mm | 167.5 mm | 167.5 mm | 167.5-175 mm |
| 34.5 in (87.6 cm) | 175 mm | 170 mm | 167.5 mm | 167.5 mm | 167.5-175 mm |
| 35.0 in (88.9 cm) | 175 mm | 170 mm | 167.5 mm | 167.5 mm | 167.5-175 mm |
| 35.5 in (90.2 cm) | 177.5 mm | 172.5 mm | 170 mm | 170 mm | 170-177.5 mm |
| 36.0 in (91.4 cm) | 177.5 mm | 172.5 mm | 170 mm | 170 mm | 170-177.5 mm |
| 36.5 in (92.7 cm) | 177.5 mm | 172.5 mm | 170 mm | 170 mm | 170-177.5 mm |
| 37.0 in (94.0 cm) | 177.5 mm | 172.5 mm | 170 mm | 170 mm | 170-177.5 mm |
| 37.5 in (95.3 cm) | 177.5 mm | 172.5 mm | 170 mm | 170 mm | 170-177.5 mm |
| 38.0 in (96.5 cm) | 177.5 mm | 172.5 mm | 170 mm | 170 mm | 170-177.5 mm |
The classic chart jumps at inseams of 29.1, 31.5, 33.9 and 35.4 in (74, 80, 86 and 90 cm). The range runs from 2.5 mm below today’s trend up to the classic length: anywhere inside it is reasonable, and it isn’t worth replacing the cranks you have.
What changes when you shorten your cranks
| Change | Saddle height | Foot at the top of the stroke | Force for the same gear | Foot speed |
|---|---|---|---|---|
| 175 → 172.5 mm | 2.5 mm higher | 5 mm lower | 1.4 % more | 1.4 % less |
| 175 → 170 mm | 5 mm higher | 10 mm lower | 2.9 % more | 2.9 % less |
| 172.5 → 170 mm | 2.5 mm higher | 5 mm lower | 1.5 % more | 1.4 % less |
| 172.5 → 167.5 mm | 5 mm higher | 10 mm lower | 3 % more | 2.9 % less |
| 172.5 → 165 mm | 7.5 mm higher | 15 mm lower | 4.5 % more | 4.3 % less |
| 170 → 165 mm | 5 mm higher | 10 mm lower | 3 % more | 2.9 % less |
| 172.5 → 160 mm | 12.5 mm higher | 25 mm lower | 7.8 % more | 7.2 % less |
| 170 → 160 mm | 10 mm higher | 20 mm lower | 6.3 % more | 5.9 % less |
The saddle goes up by as much as the crank gets shorter, so your leg reaches the same extension at the bottom. At the top, your foot ends up twice as low relative to your hip, because the raised saddle adds to the pedal not coming up as high: that’s where the comfort gain comes from. In exchange, every gear takes a little more force at the same cadence; if you notice it, shift to a bigger cog.
How to read the chart
- Between two rows. If your inseam falls between rows, use the lower one: with 31.25 in, the 31 in row. The classic chart changes abruptly at each jump; if you’re right on one, either length works.
- Custom cranks. Zinn, which makes custom cranks, suggests 21-21.6 % of inseam: with a 32 in (81.3 cm) inseam, 171-176 mm, and for long inseams it goes over 180 mm. It’s a different school of thought, aimed at very tall riders on cranks you can’t buy off the shelf.
- Knee pain or a closed hip. If your knee feels very high at the top of the stroke or you struggle to pedal in the drops, try the column for today’s trend even if your cranks are inside the range.
If you change cranks, reset your saddle with the saddle height chart by inseam (why it changes is explained in the saddle height guide) and check your gears in the gear ratio calculator. Common chainrings and cogs are in the gear ratio chart.
Frequently asked questions
What crank length do I need with a 32 inch inseam?
The classic chart says 172.5 mm, and today's trend says 167.5 mm for road or gravel and 165 mm for mountain or triathlon. Anything from 165 to 172.5 mm is reasonable on a road bike.
Do shorter cranks cost you power?
Hardly at all. Martin and Spirduso (2001) tested cranks from 120 to 220 mm with 16 cyclists: maximum power was highest with 145 and 170 mm, and only dropped with 120 and 220 mm. What changes is how each gear feels: with 165 mm instead of 172.5 mm cranks, it takes 4.5 % more force.
Is there a real difference between 170 and 172.5 mm cranks?
It's 2.5 mm: your saddle drops 2.5 mm, and with 172.5 mm cranks each gear feels about 1.5 % easier. Very few riders notice the change at the knee.