Gear ratios
Say what you weigh and what you can hold on the left, and what is on the bike on the right. It answers the question you have with a cassette in your hand: how steep a road each one would carry you up, and how fast you could still pedal. No cassette adds a watt — a bigger cog only lets you go slowly enough to survive.
Only what Shimano actually sells, because the makers no longer agree: SRAM's AXS cranks are sizes Shimano has never made, and Shimano's 54/40 is on no AXS bike. The wheel is the other half of every ratio — a gear is teeth and a rollout, not teeth alone. The tables below climb in the smaller ring and sprint in the bigger, which is what you would do.
This page is about ratios, not about what will fit. Everything below is what a gear does to your speed and your effort. Whether a cassette will actually go on your bike is a different question — cage length, the hanger, the freehub body, chain length, the frame's clearance — and the answer changes by model and by year. Take the cog you want to a shop and ask before you buy one.
Every largest cog Shimano sells, behind your 36 ring — the one you would climb in — at 250 W and 70 rpm. One row per cog, not per cassette: how steep a road you can get up depends on the easiest gear and nothing else, so an 11-28 and a 10-28 are the same answer. This is the gradient where that gear stops turning over; one percent steeper and the same legs are over their power. No cassette adds a watt — a bigger cog only lets you go slowly enough to survive.
| Biggest cog | Easiest gear | Steepest you can hold | Speed there | Sold as |
|---|---|---|---|---|
| 25t | 36 × 25 | 7.4% | 12.9 km/h | 11-25 |
| 28t | 36 × 28 | 8.5% | 11.5 km/h | 11-28 |
| 30t | 36 × 30 | 9.2% | 10.7 km/h | 11-30 |
| 32t | 36 × 32 | 9.9% | 10.1 km/h | 11-32 |
| 34t | 36 × 34 | 10.6% | 9.5 km/h | 11-34 |
| 36t | 36 × 36 | 11.3% | 8.9 km/h | 11-36 |
| 40t | 36 × 40 | 12.7% | 8.1 km/h | 11-40 |
| 42t | 36 × 42 | 13.4% | 7.7 km/h | 11-42 |
| 45t | 36 × 45 | 14.4% | 7.2 km/h | 10-45 |
| 51t | 36 × 51 | 16.5% | 6.3 km/h | 10-51 |
The other end of the same choice, and a far shorter list: ten, eleven or twelve teeth is all anyone sells. Behind your 52 ring, at 110 rpm.
| Smallest cog | Hardest gear | Still pedalling at | Sold as |
|---|---|---|---|
| 10t | 52 × 10 | 73 km/h | 10-45, 10-51 |
| 11t | 52 × 11 | 66 km/h | 11-28, 11-32, 11-34 and 5 more |
A model, not a measurement. What it can show depends on the numbers above — what you typed, and what your files recorded — and on assumptions this page states; anything it cannot stand behind says so rather than drawing a tidier line.
Assumes a seated climbing position, typical tyres and still air; on a climb those matter little next to weight and slope. Gearing is as Shimano sells it since about 2016, so a cassette listed here was made — which is not the same as it fitting your bike.
No — it makes climbing possible. No cassette adds a watt. What a bigger cog buys is the right to go slowly enough that the watts you do have are enough, at a cadence you can still turn. The work of lifting you up the hill is the same in every gear; the gear decides whether you can produce it.
That depends on what you weigh and what you can hold, which is why this page asks rather than answering in the abstract. For a 75 kg rider on a 9 kg bike holding 200 W it takes a 34×34, and even that is 60 rpm at 7.7 km/h — grinding. To keep 70 rpm on the same climb, 200 W is not enough watts for any road cassette made: a 34×36 still only holds 9.5%. Put your own numbers in above.
At the top of the block, nothing — both start at 11, so your fastest gear is identical. At the bottom the 34 lets you ride roughly a fifth slower at the same cadence, which is worth about two points of gradient to most riders. The cost is bigger jumps between the cogs in between.
Their ratios are directly comparable, which is what this page works in, but their parts often are not. Cassette spacing, freehub bodies, chain width and the pull ratio of the shifter all differ, and they differ again between generations. Check any combination with a shop before you buy it.
Because it sets both ends of the answer. The slowest cadence you will accept decides how steep a road you can get up: below it you stall, whatever the gear. The fastest you can spin decides how fast you can still pedal before you are freewheeling.