Not sure what the top speed of your project might be?
Want to make sure you don’t destroy your clutch with a gear ratio that’s too tall?
You can use this calculator to determine maximum theoretical speeds and also what the minimum speed you can travel at will be while the clutch is completely engaged. This can help determine the best ratio if you are intending on travelling slowly (for example, using off-road wheels in a paddock with kids driving).
Speed calculator
Potential Top Speed: KP/H
Minimum Speed to Fully Engage Clutch: KP/H
HOW TO USE THE CALCULATOR
The calculator is generally self-explanatory. It’s pre-filled with settings for a typical 4-stroke race-kart using one of our engines at a dirt circuit track like Ipswich City Dirt Kart Club or Ma Ma Creek. Click the Calculate button to show the speeds.
You can also modify the options to suit your specific vehcile and needs.
1. Maximum Safe Engine RPM
The drop down box includes common typical engine RPM values. If you have a different maximum RPM you’ve measured or anticipate, choose CUSTOM and enter your value in the box which appears.
If you are running a governed 4-stroke, maximum RPM will be around 3600rpm. In this case, enter 3600 into the safe maximum RPM field in the calculator
2. Tyre Diameter
The drop down box includes common typical tyre sizes for race karts, or race karts converted to off-road using our off-road wheels.
If you have a different size tyre, choose custom and enter the diameter of your tyre in mm in the box which appears.
The easiest way to determine the diameter of the tyre is to measure from the ground to the top tip of the tyre.
2. Dry Clutch or Torque Converter
The drop down box includes the two typical styles of transmission you’ll likely use on your race kart – a dry clutch (like our SR or GT clutches) or a torque converter or the 2:1 Reduction Wet Clutch fitted to certain 4-stroke engines from factory. Choose the one you have installed.
If you are using something else, you can choose Custom Diff Ratio and enter your reduction ratio in the box provided. For example if you’re using a 5:1 diff or reduction box, enter 5:1 into the box.
3. Clutch Engagement RPM
Typically you do not need to change this option. Most dry clutches will engage at approxmately 2000rpm – our SR clutches (and the default GT clutch option) will be set at this value. Torque converters will also engage at this RPM.
If you have installed different springs or are using an adjustable engagement rpm clutch, or you’re using a different system that has a different engagement speed then choose Custom and enter your known engagment RPM.
If you are using a clutch on a KT100 or 2-Stroke engine, those typically engage at 8000+ RPM. You’ll need to refer to your docmentation for your clutch and then choose Custom and enter your known engagment RPM.
4. Number of teeth on clutch (engine) sprocket
The number of teeth on yoru clutch sprocket or torque converter jackshaft sprocket or wet clutch output shaft sprocket.
If you’re using a gearbox or other custom setup, use the number of teeth on the sprocket on the output shaft of the engine.
5. Number of teeth on rear axle sprocket
The number of teeth on the large sprocket on the rear axle.
Outputs
Potential Top Speed
This is the theoretical top speed your vehicle could reach, assuming it has enough power to overcome the forces required to achieve the top speed.
For example, if you gear your vehicle with a 1:10,000 ratio you might theoretcally have a top speed of 500kph, but it is almost certain you will not have enough power to overcome the forces required to reach that top speed.
Minimum Speed to Fully Engage Clutch
This is the road speed the vehicle must be travelling at to fully engage the clutch. Anything less than this speed will be slipping the clutch, heating it up.
It is important to set this at a realistic amount. For example, if kids are using the vehicle and travelling slowly, they may rarely move faster than 10kph, which means a 10kph engagment speed would cause the vehicle to have a constantly slipping clutch, which will fail quickly. Often a torque converter can help in this situation.
