🚲 BMX Gear Ratio Calculator
Calculate gear ratio, gear inches, rollout, and speed for any BMX sprocket & cog combination
| Sprocket (T) | Cog (T) | Ratio | Gear Inches | Rollout (in) | Style |
|---|---|---|---|---|---|
| 22 | 8 | 2.75:1 | 55.0 | 172.8 | Mini BMX |
| 25 | 9 | 2.78:1 | 55.6 | 174.7 | Street / Flatland |
| 25 | 10 | 2.50:1 | 50.0 | 157.1 | Street (easy spin) |
| 28 | 10 | 2.80:1 | 56.0 | 175.9 | Park / Street |
| 28 | 9 | 3.11:1 | 62.2 | 195.5 | Park (speed) |
| 36 | 13 | 2.77:1 | 55.4 | 173.9 | Dirt / Cruiser |
| 36 | 16 | 2.25:1 | 45.0 | 141.4 | Race (junior) |
| 44 | 16 | 2.75:1 | 55.0 | 172.8 | Race Pro |
| 44 | 14 | 3.14:1 | 62.9 | 197.5 | Race (sprint) |
| 33 | 12 | 2.75:1 | 55.0 | 172.8 | All-around |
| Component | Teeth Range | BCD / Std | Chain Size | Weight (g) | Compatible |
|---|---|---|---|---|---|
| Mini Sprocket | 22–25T | 104mm / 110mm | 1/8" or 3/32" | 80–130 | Mini / Street |
| Street Sprocket | 25–30T | 110mm / 130mm | 1/8" | 120–200 | Street / Park |
| Mid Sprocket | 30–38T | 130mm | 1/8" | 150–250 | Dirt / Cruiser |
| Race Sprocket | 38–46T | 130mm / 152mm | 1/8" | 200–350 | Racing |
| Rear Cog (steel) | 9–11T | 3/8" axle | 1/8" | 40–80 | Street / Park |
| Rear Cog (race) | 13–16T | 3/8" axle | 1/8" | 55–100 | Racing |
| Half-Link Chain | N/A | 1/2" pitch | 1/8" | 280–350 | All styles |
| Standard Chain | N/A | 1/2" pitch | 1/8" | 300–380 | All styles |
| Riding Style | Ratio Range | Sprocket | Cog | Gear Inches | Cadence (RPM) |
|---|---|---|---|---|---|
| Street | 2.5–2.8:1 | 25–28T | 9–10T | 50–56 | 80–120 |
| Park / Vert | 2.7–3.1:1 | 25–30T | 9–10T | 54–62 | 90–130 |
| Flatland | 2.4–2.7:1 | 25T | 9–10T | 48–54 | 70–110 |
| Dirt Jump | 2.6–2.9:1 | 28–36T | 10–13T | 52–58 | 80–120 |
| Race | 2.6–3.2:1 | 36–44T | 13–16T | 52–64 | 120–200 |
| Cruiser (24in) | 2.3–2.7:1 | 33–38T | 13–16T | 55–65 | 70–110 |
BMX bikes have only one gear, rather than either mountain bikes, that use several gears for climbing hills and going down slopes. Hence it really matters to choose the right bmx gear. One finds it by sharing the teeth of the front star by those of the rear sprocket.
The bike gear commonly measures in “gear inches” what relates to the relation between size of front star, rear sprocket and width of the front wheel. By such math, the gear ratios help to estimate the real size of fixed wheel travel.
How to Pick the Right BMX Gear
The classic bmx gear 44/16 became standard during years, giving around 55 gear inches. This value, almost 55 gear inches, simply feels best for many riders. Most favorite ratios usually stay beside that best level.
Hunt around 54,5 until 55 gear inches well works for starts and boost speed.
Now these days, the favorite modern mix is 25-tooth front star with 9-tooth rear guide. It results in a ratio of around 2,78, very similar to the classic 44/16 setup. 25/9 already counts as standard and ensures comfortable bmx gear.
Riders that want too go more quickly can choose higher gear, for instance 28-tooth star with 9-tooth guide. Youngsters commonly choose some more bottom.
The standard BMX ratio widely estimates at 2,75. Hence with 11-tooth rear gear, 30-tooth front star answers well. Other common setups beside 2,75 are 28/10 and 30/11.
Going more than 0,5 above or under 2,75 is not really advised.
For riding street or in park, bottom gear more answers, especially when you try to reach that last shift before jumping up on ramp. For street and park, bmx gear usually is 25/9. Riders try all setups however, big gears, little front and little rear setups, and everything between.
It ultimately depends on what most answers to every person.
Big difference appears with bigger wheel sizes. Ratio of 2,8 on 20-inch wheel feels different than on big wheel, where pedaling becomes more hard. For 29-inch wheels, using something like 26/13, 28/14 or 36/18 gives almost ideal bmx gear.
Even the size of the wheels matters, difference between various tire widths indeed quite a lot matters. The usual way to estimate gear in BMX is to estimate the rounded diameter andmultiply it by the ratio.
High gear ratios indeed allow higher top speeds, but they pedal more heavily. For instance, 41/17 setup gives around 63 gear inches, a lot above the 55 standard. BMX gears are seen as fairly light compared to other bike types.
Winning the first part of the race is very important, hence the effort in the first straight always comes first, when one changes gear.
