If you’re anything like me, you know that speed and fun go hand in hand. Going slow in a go kart still feels fast with the wind whipping your hair. But how fast are you really going? The answer is a little more complicated than you’d think.
Most go karts fall in the range of 25-45mph. The variance depends on factors like drive wheel diameter, gear teeth on both the driveshaft and axle shaft, and the RPM’s the engine spins at under load. Torque converter vs clutch will also determine how fast you can go without prematurely wearing out components.
There are a few top speed calculators I’ve used in the past, but I recommend BMI Karts Calculator since it explains how to gather your data.
How to Increase Top Speed
Adjusting a single input will either reduce or increase top speed potential. Options below.
- Increase the size of your drive wheels, the ones attached to the axle turned by the engine.
- Increase the RPM’s that your engine can maintain. This is done by removing the governor and requires opening up the inside of the engine. Note: prolonged high RPM usage can damage or cause the engine to catastrophically fail.
- Reduce the size of the gear attached to the axle shaft.
- Increase the size of the gear attached to the engine shaft.
- Add a transmission. This will open up many different possibilities making your go kart more car-like and allowing some serious speed.
Note: be careful when adjusting gear sizes and make sure to measure for clearance. Consider ground clearance when adjusting the axle shaft sprocket if sizing up.
Why You Might Not Want to Increase Top Speed
Something to keep in mind here is what your adjustments will do to the drivability of your go kart. Generally, when you start adjusting gear sizes (the easiest adjustment to make) you will also adjust the effective torque. As you move around gear sizes you change the ratio between them. It’s important to remember the higher the ratio the higher the top speed, but also the lower the torque you feel.
Personally, I added a smaller sprocket on the engine shaft to decrease top speed but increase torque. This gives you more kick in the seat of your pants feeling and it’s generally more fun. Getting to the top speed in your go kart can take a little bit of time and should only be done in situations where you have enough room to safely slow down.
If you are using your go kart on trails or around corners or in the woods, you will likely want to go with a more torque based sprocket. If you are in open spaces where speed is not limited, topping out your go kart can be exhilarating.
Best of Both Worlds
If you’re the have your cake and eat it too type of person, you’re in luck!
To achieve more torque and maintain your top speed, removing the governor might be something you should consider. If you size down on your drive sprocket (the one that connects to the engine), your top speed will go down. But if you remove the governor and allow the engine to spin at higher RPM’s you can maintain the original top speed.
Most small 5-6.5hp engines will sping upwards of 5300 RPM’s before the valves will float and you won’t be able to go any faster. It is important to note here though that spinning your engine at higher RPM’s for prolonged periods of time will damage the engine, and could possibly cause parts of it to fail. It is possible however to upgrade your engine parts to make sustained high RPM’s safe.
Horsepower to Top Speed Correlation
What we’ve learned from cars is the higher the horsepower, the faster the car. When it comes to go karts, unfortunately, that isn’t the case. That doesn’t mean you couldn’t benefit from a higher HP engine though. Upgrading your engine can be a great replacement for lost torque if you adjust your gearing for top speed. Higher horsepower engines will allow you to still feel a good grunt of power, and with a higher gear ratio, you can still achieve higher top speeds.
Just be careful when you upgrade your engine. As you introduce more HP you will need to make sure your drive system, either a clutch or torque converter, will be able to handle the extra HP. This is also true when it comes to top speed.
Clutch and Torque Converter Considerations
Gear ratios should remain within 4:1 and 7:1 for longer life out of your clutch or torque converter belt. Torque converters can handle more abuse so they can handle the extremes of either side of this range. Just know the further away from a 5:1 or 6:1 ratio the more wear you are causing and will lead to replacing the clutch or torque converter belt sooner.
Conclusion
As you can see, adjusting top speed has a lot of variables. Consider your usage and top speed goals and search for available sprocket sizes, that will give you an idea to plug into the calculator and make your decision easier based on what parts are available. Have fun out there!
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