Choosing the right gear ratio is essential for getting the most out of your engine. The right gear will keep your engine in its power band, giving you maximum acceleration off the corners and optimal RPM down the straightaways. Use these charts as a starting point and adjust based on track conditions and your specific setup.
How to Read These Charts
Gear ratio is calculated by dividing the number of teeth on the axle sprocket (driven) by the number of teeth on the clutch (driver). For example, a 60-tooth axle sprocket and a 15-tooth clutch gives a ratio of 60/15 = 4.00:1.
Ratio = Axle Sprocket Teeth / Clutch Teeth
Example: 60 / 15 = 4.00:1
Higher ratio (e.g., 5.50:1): More acceleration, less top speed. Good for small, tight tracks.
Lower ratio (e.g., 4.20:1): More top speed, less acceleration. Good for large, sweeping tracks.
Honda GX120 / GX160
These engines are torque-rich and work well with a variety of ratios. These recommendations are for stock or lightly modified Honda engines in quarter midget classes.
| Track Size | Track Type | Typical Ratio | Clutch / Axle Combo |
|---|---|---|---|
| 1/20 mile or smaller | Tight bullring | 5.80 - 6.20 : 1 | 15/87 to 15/93 |
| 1/16 mile | Medium, flat | 5.20 - 5.60 : 1 | 15/78 to 15/84 |
| 1/16 mile | Medium, banked | 5.00 - 5.40 : 1 | 15/75 to 15/81 |
| 1/10 mile | Large, flat | 4.80 - 5.20 : 1 | 15/72 to 15/78 |
| 1/10 mile | Large, banked | 4.60 - 5.00 : 1 | 15/69 to 15/75 |
Note: Honda 160 engines can often pull slightly taller (lower number) gears than Honda 120s due to increased torque. If running a 160, you may drop ratio by 0.1-0.2 from these recommendations.
Briggs & Stratton Animal
The Animal engine has a broader power band than the Honda and typically requires slightly different gearing. These recommendations are for stock or mildly modified Animals.
| Track Size | Track Type | Typical Ratio | Clutch / Axle Combo |
|---|---|---|---|
| 1/20 mile or smaller | Tight bullring | 5.40 - 5.80 : 1 | 15/81 to 15/87 |
| 1/16 mile | Medium, flat | 5.00 - 5.40 : 1 | 15/75 to 15/81 |
| 1/16 mile | Medium, banked | 4.80 - 5.20 : 1 | 15/72 to 15/78 |
| 1/10 mile | Large, flat | 4.60 - 5.00 : 1 | 15/69 to 15/75 |
| 1/10 mile | Large, banked | 4.40 - 4.80 : 1 | 15/66 to 15/72 |
World Formula
The World Formula is a purpose-built racing engine with a different power curve. These charts are for stock World Formula engines.
| Track Size | Track Type | Typical Ratio | Clutch / Axle Combo |
|---|---|---|---|
| 1/20 mile or smaller | Tight bullring | 5.20 - 5.60 : 1 | 15/78 to 15/84 |
| 1/16 mile | Medium, flat | 4.80 - 5.20 : 1 | 15/72 to 15/78 |
| 1/16 mile | Medium, banked | 4.60 - 5.00 : 1 | 15/69 to 15/75 |
| 1/10 mile | Large, flat | 4.40 - 4.80 : 1 | 15/66 to 15/72 |
| 1/10 mile | Large, banked | 4.20 - 4.60 : 1 | 15/63 to 15/69 |
Modified / Open Engines
Modified engines (like the Modified World Formula or open animals) produce more power and often higher RPM. They can typically pull taller gears (lower ratio). These are general guidelines only—consult your engine builder for specific recommendations.
| Track Size | Typical Ratio Range | Notes |
|---|---|---|
| 1/20 mile or smaller | 5.00 - 5.40 : 1 | Higher RPM engines may need more gear |
| 1/16 mile | 4.60 - 5.00 : 1 | Adjust based on corner exit power |
| 1/10 mile | 4.20 - 4.60 : 1 | Watch RPM at end of straight |
Quick Reference Gear Chart
This table shows common gear ratios based on clutch and axle sprocket combinations. Find your clutch teeth on the left, axle teeth on the top, and the intersection is your ratio.
| Clutch \ Axle | 60 | 61 | 62 | 63 | 64 | 65 | 66 | 67 | 68 | 69 | 70 | 71 | 72 | 73 | 74 | 75 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 14 | 4.29 | 4.36 | 4.43 | 4.50 | 4.57 | 4.64 | 4.71 | 4.79 | 4.86 | 4.93 | 5.00 | 5.07 | 5.14 | 5.21 | 5.29 | 5.36 |
| 15 | 4.00 | 4.07 | 4.13 | 4.20 | 4.27 | 4.33 | 4.40 | 4.47 | 4.53 | 4.60 | 4.67 | 4.73 | 4.80 | 4.87 | 4.93 | 5.00 |
| 16 | 3.75 | 3.81 | 3.88 | 3.94 | 4.00 | 4.06 | 4.13 | 4.19 | 4.25 | 4.31 | 4.38 | 4.44 | 4.50 | 4.56 | 4.63 | 4.69 |
| 17 | 3.53 | 3.59 | 3.65 | 3.71 | 3.76 | 3.82 | 3.88 | 3.94 | 4.00 | 4.06 | 4.12 | 4.18 | 4.24 | 4.29 | 4.35 | 4.41 |
| 18 | 3.33 | 3.39 | 3.44 | 3.50 | 3.56 | 3.61 | 3.67 | 3.72 | 3.78 | 3.83 | 3.89 | 3.94 | 4.00 | 4.06 | 4.11 | 4.17 |
| 19 | 3.16 | 3.21 | 3.26 | 3.32 | 3.37 | 3.42 | 3.47 | 3.53 | 3.58 | 3.63 | 3.68 | 3.74 | 3.79 | 3.84 | 3.89 | 3.95 |
| 20 | 3.00 | 3.05 | 3.10 | 3.15 | 3.20 | 3.25 | 3.30 | 3.35 | 3.40 | 3.45 | 3.50 | 3.55 | 3.60 | 3.65 | 3.70 | 3.75 |
Gearing Tips & Guidelines
When to Go Higher Ratio (More Gear)
- Small, tight tracks
- Slick, low-grip conditions
- Car is bogging off corners (too tall a gear)
- Engine RPM is too low on straightaways
When to Go Lower Ratio (Less Gear)
- Large, sweeping tracks
- High-grip, tacky conditions
- Engine RPM is too high (over-revving)
- Car runs out of RPM before end of straight
Using RPM to Fine-Tune
If you have a tachometer, use it to dial in your gearing. After a practice session, note your max RPM on the straightaway. Ideally, you want to be just below your engine's peak power RPM at the end of the longest straight. If you're hitting the rev limiter or exceeding recommended max RPM, go to a taller gear (lower ratio). If you're not getting close to peak RPM, go to a shorter gear (higher ratio).
Typical RPM Ranges
| Engine | Peak Power RPM | Max Recommended RPM |
|---|---|---|
| Honda GX120 | 4,000 - 4,500 | 5,000 |
| Honda GX160 | 4,200 - 4,700 | 5,200 |
| Briggs Animal (stock) | 4,500 - 5,000 | 5,500 |
| World Formula (stock) | 5,000 - 5,500 | 6,000 |
| Modified / Open | 5,500 - 6,500+ | Varies (check builder) |
Other Factors Affecting Gearing
- Driver weight: Heavier drivers may need slightly more gear (higher ratio).
- Track configuration: Long straightaways with tight corners need different gearing than short straights with sweeping corners.
- Stagger: Changing rear stagger effectively changes your gear ratio. More stagger (larger RR) acts like a taller gear.
- Weather: On hot, humid days, engines make less power and may need more gear. On cool, dense air days, they make more power and can pull taller gears.
Final Notes
These charts are starting points. Every track is different, and every driver has their own preference. The best way to find the perfect gear is to test, take notes, and adjust based on lap times and how the car feels. If you're unsure, start in the middle of the recommended range and adjust from there.
For more help with gearing or to discuss your specific setup, please contact us. We're happy to help you find the right gear for your combination.