Compare two drivetrain setups side by side. See how a cassette or chainring upgrade changes your climbing and top-end gears.
When you consider upgrading your cassette or chainring, you need to know: will I get an easier climbing gear? Will my top speed change? This calculator shows you both setups at a glance.
Gear ratio is front teeth divided by rear teeth. A smaller rear cog (like 11 teeth) gives a high ratio: you pedal less often but go fast. A bigger rear cog (like 36 teeth) gives a low ratio: you pedal more often but can climb steep hills. Development is the distance you travel per pedal stroke, combining the gear ratio with your wheel size. Gain ratio accounts for crank length too, so it lets you compare bikes with different cranks fairly.
The easiest gear (lowest ratio, highest cadence for a given speed) is always your smallest chainring paired with your biggest cog. If you upgrade from a 28-tooth cog to a 36-tooth cog, your climbing gear becomes significantly easier, especially on very steep terrain. The calculator shows which of your new gears you have never had before (marked "NEW").
| Type | Range | Use case |
|---|---|---|
| Road compact crankset Chainrings | 50/34T | Flat terrain, light climbing. 34T chainring makes your lowest gear easy. |
| Road standard crankset Chainrings | 53/39T | Racing, flats, rolling terrain. Loses a few percent efficiency vs compact but holds high speed better. |
| Road cassette (tight) Shimano 105/Ultegra | 11-28T | Racing, flat terrain. Close gear spacing, no bailout climbing gear. |
| Road cassette (moderate) Most all-rounders | 11-32T | Mixed terrain, long rides. Balances speed on flats with usable climbing gears. |
| Road cassette (wide) Gravel, climbing | 11-34T or 11-36T | Gravel, hilly areas, loaded touring. The 34 or 36T gives real bailout gears on steep climbs. |
| Mountain bike cassette Trail / XC | 11-42T or 11-46T | Steep terrain, variable surfaces. Wide range lets you stay in the right gear for technical sections. |
| Single-speed or track Fixed ratio | 16/17T cog only | Urban, velodrome. No shifting, high durability. |
Tire width changes the effective wheel diameter, which changes development (distance per pedal stroke). A 23mm road tire on a 700c wheel has a smaller circumference than a 28mm tire on the same rim. This table gives circumference in metres for ISO 5775-standard tires.
| Rim / Tire | Circumference (m) | Notes |
|---|---|---|
| 700c (622mm rim) 18mm | 2.05 | Very narrow, track or road racing only |
| 700c 23mm | 2.08 | Road racing, minimal rolling resistance |
| 700c 25mm | 2.11 | Road / gravel balance, most common |
| 700c 28mm | 2.14 | Gravel-friendly, comfort for road |
| 700c 32mm | 2.17 | Gravel bike standard |
| 700c 40mm | 2.23 | Wide gravel, adventure bikes |
| 650c (571mm rim) 25mm | 1.93 | Compact road bikes, smaller riders |
| 27.5" (584mm rim) 2.0" | 2.07 | MTB standard, steep terrain |
| 27.5" 2.4" | 2.19 | Trail MTB, more grip, bigger roll-over |
| 29" (622mm rim) 2.1" | 2.35 | XC MTB, fast rolling, fewer pedal strokes |
| 29" 2.4" | 2.43 | Trail 29er, good for rough terrain |
| 26" (559mm rim) 1.5" | 1.83 | Older MTB, still common in developing regions |
| 26" 2.0" | 1.95 | Older trail bike standard |
| 26" 2.4" | 2.07 | Wider old-school MTB tires |
Why these numbers matter: A 23mm tire is 1.3 per cent shorter circumference than a 28mm tire on the same rim. If you only change your cassette but not your tire, you might not notice. If you change wheels entirely (say, from 26" to 29"), your development numbers shift by over 25 per cent for the same gear combination. Always plug in your actual tires and rims.
Gain ratio is a way of comparing gears across bikes with different crank lengths. Most riders do not swap cranks, so gain ratio matters mainly when you are comparing your setup to someone else's bike or reading a bike review that uses the term.
Standard crank lengths: 170mm for small riders, 172.5mm for most, 175mm for larger riders or in older bikes. Some mountain bikes use 175mm. Track cyclists sometimes use 165mm or 167.5mm to gain pedal clearance. Longer cranks give a longer pedal stroke and a slight mechanical advantage, but also raise your body position on the bike and can clip your heel on obstacles. Most riders never change cranks unless upgrading to a full new crankset.
This calculator includes gain ratio for reference. When comparing two of your own bikes, you usually only care about development unless the crank lengths differ significantly.
You ride a 700c road bike, compact crank (50/34T), 11-28T cassette, standard 172.5mm cranks, 25mm tires. You are considering a 11-34T cassette.
Your current low gear: 34T chainring, 28T cog. Gear ratio = 34/28 = 1.21. On a 700c wheel (2.11m circumference), development = 1.21 * 2.11 = 2.55 metres per pedal stroke. At 90 RPM, speed = 2.55 * 90 * 60 / 1000 = 13.8 km/h. This is already a climbing gear, not bad for a compact.
With the upgrade: 34T chainring, 34T cog. Gear ratio = 34/34 = 1.0. Development = 1.0 * 2.11 = 2.11 metres. At 90 RPM, speed = 2.11 * 90 * 60 / 1000 = 11.4 km/h. This is notably easier, lets you climb at a higher cadence, or stay seated on steeper terrain. You gain a second climbing gear and do not lose any top-end speed (still 50T chainring, 11T cog at 9.6 m/s or 34.6 km/h).
The tradeoff: Upgrading to an 11-34T cassette adds weight (about 50g). You need a derailleur rated for 34T (most modern long-cage derailleurs are). The third-smallest cog (17T) is now slightly further from the 14T and 11T gears, but the shift quality on modern drivetrains is excellent and you will not notice. The upgrade is cheap (often under 100 USD), gives you two new, easier gears, and costs nothing in efficiency or speed. Almost always worth it if you ride hilly terrain.
Gear ratio is the number of teeth on the front chainring divided by the number of teeth on the rear cog. A 50-tooth chainring with a 15-tooth cog gives a gear ratio of 3.33, meaning the rear wheel turns 3.33 times for each pedal revolution. Higher ratios are harder to pedal but cover more ground per stroke.
Development, also called rollout, is the distance your bike travels per complete pedal revolution. It equals gear ratio multiplied by wheel circumference. It lets you compare gears fairly between bikes with different wheel sizes. A larger development means more distance per pedal stroke.
Gain ratio, proposed by Sheldon Brown, is the ratio of pedal travel distance to wheel travel distance. It accounts for crank length, which gear inches and development do not. The formula is (wheel radius divided by crank length) times (front teeth divided by rear teeth). Two bikes with identical chainring and cog combinations but different crank lengths will have different gain ratios.
Compare the lowest gears (largest rear cog) of both setups using this calculator. If the new cassette has a bigger cog than your current one, your climbing gear becomes easier. A 34-tooth cog is easier than a 28-tooth. You can also compare the full range: if the new cassette goes up to 36 teeth, you now have one extra, easier gear for very steep climbs.
Cadence is pedal revolutions per minute. Most cyclists ride efficiently at 80-100 RPM. The calculator shows speed at your chosen cadence. If you usually ride at 90 RPM, enter 90. Road cyclists often cruise at 85-95 RPM, while mountain bikers in technical terrain may drop to 60-80 RPM.