Quick Reference
Common combos & ratios by dirt bike class
Common Sprocket Combinations
| Bike class | Common range | Typical | Ratio (R/F) |
|---|
| 85cc | 13 / 46–48 | 13 / 47 | 3.62 |
| 125cc 2-stroke | 13 / 50–52 | 13 / 50 | 3.85 |
| 150cc 2-stroke | 13 / 49–51 | 13 / 50 | 3.85 |
| 250cc 2-stroke | 13 / 49–51 | 13 / 50 | 3.85 |
| 250cc 4-stroke | 13 / 50–52 | 13 / 51 | 3.92 |
| 300cc 2-stroke | 13 / 50–52 | 13 / 51 | 3.92 |
| 350cc 4-stroke | 13 / 50–52 | 13 / 51 | 3.92 |
| 450cc 4-stroke | 14 / 48–51 | 14 / 49 | 3.50 |
| 500cc 2-stroke | 14 / 49–51 | 14 / 50 | 3.57 |
| Open (600+cc) | 15 / 47–50 | 15 / 49 | 3.27 |
Chain Specs
| Class | Chain | Pitch | Links | Note |
|---|
| 85cc–150cc | 420 | 1/2" | 120–128 | Lightweight; mini / small bikes |
| 125cc–250cc | 520 | 5/8" | 120–126 | Most common dirt bike chain |
| 250cc–450cc | 520 | 5/8" | 120–126 | Standard for modern 4-strokes |
| 500cc+ / Open | 520 / 530 | 5/8" | 120–128 | 530 for high-torque applications |
Standard Gear Ratios
| Bike class | Primary | Gearbox | Typical final |
|---|
| 125cc 2-stroke | 3.36 | 1st 2.50 · 2nd 1.78 · 3rd 1.29 · 4th 1.00 · 5th 0.83 | 3.85 |
| 250cc 2-stroke | 3.13 | 1st 2.42 · 2nd 1.73 · 3rd 1.25 · 4th 1.00 · 5th 0.84 | 3.85 |
| 250cc 4-stroke | 2.74 | 1st 2.42 · 2nd 1.86 · 3rd 1.42 · 4th 1.16 · 5th 1.00 | 3.92 |
| 450cc 4-stroke | 2.65 | 1st 2.36 · 2nd 1.78 · 3rd 1.36 · 4th 1.10 · 5th 1.00 | 3.50 |
| 500cc 2-stroke | 2.93 | 1st 2.50 · 2nd 1.78 · 3rd 1.29 · 4th 1.00 · 5th 0.83 | 3.57 |
Values are general guides per class — always confirm against your specific model’s manual before finalizing a setup.