Training Tools
BMX Gear Calculator
Calculate BMX gear ratio, gear inches, roll-out and top speed for 20" BMX and 24" Cruiser. Uses actual BSD wheel diameters for accurate results.
Quick Presets
Your Setup
Effective outer diameter: 19.98" (507.6mm)
Speed at Cadence
Speed
18.0
mph
Speed
28.9
km/h
8.04 m/s
Results
Gear Ratio
2.750
:1
Gear Inches
55.0"
1396mm
Roll-Out
172.7"
inches
Roll-Out
439
cm
Roll-Out
4.39
metres
44T / 16T on a 20" BMX (Standard) with 2" tyres. Each complete pedal revolution moves you 4.39m.
Gear Ratio Matrix
| F \ R | 13T | 14T | 15T | 16T | 17T | 18T |
|---|---|---|---|---|---|---|
| 36T | 2.77 | 2.57 | 2.40 | 2.25 | 2.12 | 2.00 |
| 39T | 3.00 | 2.79 | 2.60 | 2.44 | 2.29 | 2.17 |
| 40T | 3.08 | 2.86 | 2.67 | 2.50 | 2.35 | 2.22 |
| 41T | 3.15 | 2.93 | 2.73 | 2.56 | 2.41 | 2.28 |
| 42T | 3.23 | 3.00 | 2.80 | 2.63 | 2.47 | 2.33 |
| 43T | 3.31 | 3.07 | 2.87 | 2.69 | 2.53 | 2.39 |
| 44T | 3.38 | 3.14 | 2.93 | 2.75 | 2.59 | 2.44 |
| 45T | 3.46 | 3.21 | 3.00 | 2.81 | 2.65 | 2.50 |
★ Typical elite race range. Click any cell to select that combo.
What does this mean?
Gear Ratio
How many times the rear wheel rotates for each complete pedal revolution. A 2.75:1 ratio means the wheel spins 2.75 times per pedal stroke.
Gear Inches
The equivalent diameter of a penny-farthing wheel that would give the same mechanical advantage. Higher = harder to push, more top speed.
Roll-Out
The distance the bike travels per complete pedal revolution. Calculated using the actual outer wheel diameter (BSD + 2× tyre section height).
BSD (Bead Seat Diameter)
The true wheel size measured at the tyre bead. 20" BMX = 406mm BSD. 24" Cruiser = 507mm BSD. More accurate than nominal sizing for calculations.
British Cycling: Clipless Pedal Rules
Under British Cycling BMX Racing Rules, riders under the age of 13 are not permitted to use clipless (clip-in) pedals at any sanctioned event. This rule applies at club, regional, and national level competition.
Riders aged 13 and over may use clipless pedals. Parents and riders should verify eligibility with event officials if unsure. Rules are reviewed annually — always check the current rulebook before the start of each season.
British Cycling BMX Rules →BMX Gear Calculator — Common Questions
What is a good BMX gear ratio for racing?
For 20" BMX racing, 44/16 (2.75:1) is the standard for Pro-size riders and the most common setup on complete Pro race bikes. Smaller riders run progressively lower ratios: complete Micro bikes typically ship 36/14, Minis run 39/16, Juniors 40/16, and Experts 42/16. The right ratio depends on track length, your strength, and your age category. Use the calculator above to compare roll-out distances.
What is roll-out in BMX racing?
Roll-out is the distance your bike travels per complete crank revolution. It is calculated from your gear ratio multiplied by wheel circumference (using BSD + tyre width for accuracy). Roll-out is critical for gate starts — a higher roll-out means more ground covered per pedal stroke, but requires more force to turn the cranks.
What are gear inches in BMX?
Gear inches is a standardised comparison metric calculated as (chainring ÷ sprocket) × wheel diameter in inches. Higher gear inches means a harder, faster gear. It is useful for comparing setups across different wheel sizes, such as 20" BMX vs 24" Cruiser.
What BMX gearing should a beginner use?
Beginners on a 20" race bike should match the gearing their complete bike was supplied with. Micros (riders up to 4ft) typically run 36/14, Minis (4ft 2" – 4ft 10") run 36/14 to 39/16, and Juniors (4ft 6" – 5ft 1") run 40/16. These ratios are tuned to the rider's power and let you focus on gate technique. As you build strength and move up a frame size, the chainring goes up with you.
What is the difference between 20" BMX and 24" Cruiser gearing?
A 24" Cruiser has a larger wheel (507mm BSD vs 406mm for 20" BMX), so the same chainring and sprocket produces a much higher roll-out and top speed. Cruiser riders typically run the same or lower ratios than 20" to compensate, or use the same ratio to maximise speed.
Is a 44/16 gear ratio good for BMX?
44/16 (2.75:1) is the most popular gear ratio in competitive 20" BMX racing. It offers a good balance of gate acceleration and straight-line speed for most track lengths. Many elite riders use 44/16. However, shorter or technical tracks sometimes favour slightly lower ratios for quicker acceleration out of turns.
Training with Runnymede Rockets in Addlestone, Surrey? Our coaches can help you dial in the perfect gear setup for your age, ability and the track.
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