One of the most crucial things to set up on a go-kart is an optimal gear ratio. An optimal gear ratio enables you to get the most out of your kart when racing on a track. The gear ratio has a direct effect on the acceleration and top speed, which is a crucial element around corners and straight sections.
However, finding the optimal gear ratio may not always be that easy and you’ll definitely need some tools. To help you with that, I’ve created a go-kart gear ratio chart and speed calculator. I’ve also included guides and tips, so that you can find the optimal gear ratio for your go-kart.
- Gear Ratio and Speed Calculator
- Gear Ratio Chart
- What is a Gear Ratio?
- How are Gear Ratios Calculated?
- Calculating Top Speed With Gear Ratios
- Best Gear Ratio for Go-Karts
1. Gear Ratio and Speed Calculator
You can easily calculate your desired gear ratio and top speed of your go-kart by entering the engine speed, engine sprocket teeth, axle sprocket teeth and tire height. There’s also an option to enable a jackshaft if you’re running a torque converter instead of a clutch.
How to Use the Gear Ratio and Speed Calculator
There are four values that you have to input or select, in order for the calculator to determine your go-kart’s top speed and gear ratio. Two optional values are required if you have a jackshaft. You can refer to the description below for further reference.
Required Values: Engine RPM - The highest rpm value of the engine (for example, select 3,500 if the range is 2,800 to 3,500). You’ll be able to find this value in your owner’s manual. Engine Sprocket (Teeth) - The number of teeth on the engine/crankshaft sprocket. If you’re running a clutch, use the number of teeth on the clutch sprocket instead. Axle Sprocket (Teeth) - The number of teeth on the sprocket that is located on your rear axle. Tire Height (Diameter) - The height of your go-kart tires (Take the first number, for example: 11 x 6.00 - 5). For more information, read the guide on how to read go-kart tire sizes. Optional Values: Jackshaft Input Sprocket (Teeth) - The number of teeth on the input sprocket of your jackshaft (leading from the engine to the jackshaft) - Optional Jackshaft Output Sprocket (Teeth) - The number of teeth on the output sprocket of your jackshaft (leading out of the jackshaft to the rear axle) - Optional
2. Gear Ratio Chart
Here’s a comprehensive go-kart gear ratio chart that accounts for the most common sprocket sizes. This chart shows the gear ratio for engine sprocket sizes from 8 – 20 teeth and axle sprocket sizes from 50 – 110 teeth.
How to Read the Gear Ratio Chart
Reading the gear ratio chart is relatively simple. The top row refers to the amount of teeth on the engine sprocket of your go-kart. If you’re using a clutch, you’ll need to refer to the clutch sprocket instead. The range is from 8 to 20 teeth)
The first column on the left indicates the number of teeth on the rear axle sprocket. The range is from 50 to 110 teeth. In order to find the gear ratio, locate both the number of teeth on the top and the left most column and trace the ratio accordingly.
Example: A go-kart with an engine/clutch sprocket (12 teeth) and a rear axle sprocket (75 teeth) has a gear ratio of 6.25 or 6.25:1.
3. What is a Gear Ratio on a Go-Kart?
Understanding the importance of optimal great ratios will enable you to maximize the efficiency and power output of your go-kart. Finding the proper gear ratio will allow you to also increase or decrease the go-karts output torque and top speed.
Let’s go into a little more detail on what a gear ratio is and how you can easily understand the concept. A typical racing go-kart has two sprockets, one located at the crankshaft (or on the clutch) and the other on the rear axle.
Let’s go through an example. Both of the sprockets have the same amount of teeth. That would mean that for each rotation of the first sprocket, the second sprocket would turn equally as much, as they are exactly the same size. In this example the rear ratio is 1:1.
Now, take a look at the image above. The sprocket on the engine/clutch (B) has 12 sprocket teeth and the rear axle sprocket (A) has 36 teeth (three times the amount of teeth). That would mean the first sprocket needs three complete revolutions, so that the rear sprocket completes one. Here, the gear ratio is 3:1.
Do All Go-Karts have Gear Ratios?
Every go-kart will have a great ratio, as the engine transmits power from the crankshaft to the rear axle, through at least two sprockets. Technically, you could have two same-sized sprockets, but that would rip your clutch and chain apart, as there is just way too much torque.
Therefore, go-kart racers typically opt for a higher gear ratio so that they are able to balance performance against component wear effectively. They’re also able to calibrate go-kart acceleration and top speed (important for corners and straight sections). The general rule is: the lower the gear ratio, the higher the top speed of a go-kart.
4. How are Go-Kart Gear Ratios Calculated?
Determining the gear ratio on your go-kart is simple. All you need to do is divide the number of teeth on the rear axle sprocket by the number of teeth on the clutch/engine sprocket.
Gear Ratio = Teeth on Axle Sprocket / Teeth on Clutch or Engine Sprocket
For example, a go-kart has a clutch sprocket with 12 teeth and a rear axle sprocket with 54 teeth. Simply divide 54 by 12 and you have established the gear ratio, which in this case is 4.50:1.
5. Calculating the Top Speed With Gear Ratios
Knowing the gear ratio, rpm and tire height will also allow you to calculate your go-kart’s top speed. I’ll spare you the slightly complex calculations, but you can use the gear ratio and top speed calculator that I have created for this. Here’s a quick summary of the information you’ll need:
- Engine/Clutch Sprocket Teeth
- Rear Axle Sprocket Teeth
- Tire Height (Diameter)
- Engine Max RPM
You can also use the go-kart speed calculator and work backwards to find the optimal gear ratio. This means that you can look at the desired speed you are aiming for and adjust the sliders on the sprockets to determine which gear ratio you should go for. Be sure to enable the jackshaft feature if you’re running a jackshaft on your kart.
One word of caution! You’ll also need to account for the additional stress on your go-kart parts the lower you configure your gear ratio. While a lower gear ratio equates to higher top speeds, you wouldn’t want to wreck your kart. So, it’s best to make small increments through trial and error.
6. What’s the Best Gear Ratio for Go-Karts?
Here’s the thing, there is no ‘golden gear ratio’ that anyone can give you. However, there are certain ranges where it’s most likely going to be. The reason for this is because every go-kart is different.
Not only does the optimal gear ratio for go-karts depend on the engine’s rpm, tire height and number of teeth on both sprockets, but it also depends on your transmission and go-kart type, as well as how your go-kart is built and what purpose it serves.
For racing go-karts you may use the chart below as general reference.
|2-Stroke Engine||18:1 to 15:1||15:1 to 12:1||12:1 to 8:1|
|4-Stroke Engine||10:1 to 8:1||8:1 to 6:1||6:1 to 4:1|
I would like to stress again that you should conduct all your tests in small increments and observe the performance and parts of your go-kart well. The best results arise from practice, attention to detail and plenty of trial and error. All the best!