CalculatorsBicycle Gear Ratio Calculator
Shimano Deore XT M8100 34 gearing with Shimano Deore XT M8100 10-51T
Classic XC and Trail mountain bike chainring with Dynamic Chain Engagement+. Smooth-shifting Hyperglide+ MTB cassette with a 510% gear range.
Easiest 0.66, hardest 3.40
The easiest gear (34 / 51) gives a ratio of 0.66, and the hardest (34 / 10) gives 3.40.
This is a winch gear for steep or loaded climbs. On flat ground it is far too light, so you will shift up as soon as the grade eases. The spread from 0.66 to 3.40 is wide, so the cassette is doing the work of a much bigger chainring jump.
Shimano Deore XT M8100 is a 1x MTB chainring (Direct Mount, 12-speed), here on the 12-speed Shimano cassette (MicroSpline freehub). Both parts are catalogued as MTB, and the cassette speed sits on the chainring’s compatible-speed list.
Every chainring tooth against every cog
| Chainring | 10 | 12 | 14 | 16 | 18 | 21 | 24 | 28 | 33 | 39 | 45 | 51 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 34 | 3.40 Hardest | 2.83 | 2.42 | 2.12 | 1.88 | 1.61 | 1.41 | 1.21 | 1.03 | 0.87 | 0.75 | 0.66 Easiest |
The Result is indicative and educational. It does not constitute a design, a technical opinion or medical advice and does not replace calculations or verification by a person with the appropriate qualifications and authorisations. Before purchase, installation or use in practice – in particular in electrical installations – the Result should be verified by a qualified specialist. Details: Terms of Service, point 4.
Inputs
Results
- Gear ratio
- 3.40
The Result is indicative and educational. It does not constitute a design, a technical opinion or medical advice and does not replace calculations or verification by a person with the appropriate qualifications and authorisations. Before purchase, installation or use in practice – in particular in electrical installations – the Result should be verified by a qualified specialist. Details: Terms of Service, point 4.
How the number is made
Ratio = chainring ÷ cog. Published figures are truncated to two decimal places, so 36 ÷ 34 is shown as 1.05 and 52 ÷ 11 as 4.72. The live form uses the same truncation.
The ratio is how many times the rear wheel turns for each crank revolution. It ignores wheel size; gear inches and roll-out add the tyre.
- Gear ratio. Truncated to two decimal places.
How pair pages are chosen
A chainring is paired with a cassette only when the cassette speed is in the chainring’s compatible-speed list. A track ring and a 12-speed cassette are not given a URL.
Related calculators
- Gear Inches and Roll-out Calculator
Same teeth, different development once the wheel size is in the sum.
- Cadence to Speed Calculator
Turns this ratio into km/h at the cadence you actually hold.
- Cassette Range Calculator
The percent range is the cassette alone, before a chainring is chosen.
Questions
What is a climbing ratio?
Around 1.0 or below (for example 36÷34 or 34÷51) lets you spin a steep grade. Above 1.5, the easiest gear is already hard work.
Why truncate to 1.05 instead of rounding to 1.06?
36÷34 is 1.0588. This site truncates to two decimals so every pair page quotes the same published figure.
Does the chainring brand change the ratio?
No. Teeth do. Brand, speeds and freehub decide whether the pair can be built.
Example products
Product links are Affiliate Links to Amazon websites. Using them does not cost you anything extra, and if you make a purchase we may receive a commission. Details: Terms of Service, point 5.
- Replacement cassette
Match the freehub (HG, Micro Spline, XD, XDR) before the tooth count.
$40–$400
- Matching chain
Speed count of the chain has to match the cassette, not just the chainring brand.
$20–$80