The centrifugal clutch on your kart plays a vital role in its performance. There are different types of clutches that you can fit into the drive shaft of your kart. Therefore, you might be wondering what the difference is between 10-tooth and the 12-tooth clutches.
The 3 key differences between 10-tooth and 12-tooth go-kart clutches are:
- Number of teeth
- Gear ratio
- Chain compatibility
There are a few reasons you might want to change the clutch on your kart. After reading this article, you’ll have a better understanding of the performance effect that these two clutches have on the kart, and from there you can decide whether it’s a setup element that you want to tinker with.
3 Key Differences Between 10-Tooth & 12-Tooth Clutches
1. Number Of Teeth
The first and the most obvious key difference between these two clutches is the number of teeth they have. Just like the sprockets on your rear axle, the clutches have teeth that connect to the chain. The teeth hold the chain in place, and as the clutch is on the drive shaft, they are responsible for pulling the chain as well.
You’re probably familiar with different sprockets on the axle of your kart. The 57 sprocket has 57 teeth, just like the 85 sprocket has 85 teeth, and so on. The same rule applies when it comes to the clutch that is attached to the engine. The 10-tooth clutch (10T) has 10 teeth, and the 12-tooth clutch (12T) has 12 teeth.
If you’re trying to determine which clutch you have fitted to your kart, all you need to do is count the number of teeth on the clutch. There’s usually also a noticeable difference in the size of the cog when you hold them side by side. The 10T has a larger cog than the 12T, which is slightly smaller as it needs to fit more teeth around the cog.
2. Gear Ratio
Just like with sprockets, the difference in teeth will make a difference in the gear ratio of the kart. Gear ratio can sometimes be tricky to get right, especially if you’re participating in a traveling championship and you need to adapt to different circuits for each event that you’re racing in.
Gear ratios are always confusing, and it’s easy to forget what the exact definitions of taller and shorter gearing are, so we’re going to keep it as simple as possible. Changing your clutch will affect the kart’s overall straight line speed, and you’ll either have a higher top speed, or faster acceleration out of the corners.
The gear ratio of your kart is determined by the number of teeth on the sprocket and the clutch. There’s a formula that allows you to calculate your exact gear ratio, but most drivers won’t use it because reading and understanding gear ratios is complicated. Either way, you can use the equation below if you need to:
Gear ratio = number of teeth of rear axle sprocket / number of teeth on the clutch
60 teeth on the rear axle / 12 teeth on the clutch = 5:1 gear ratio (60/12 = 5)
Which Clutch Is Faster?
The lower the gear ratio, the higher the kart’s top speed. The higher the gear ratio, the faster the kart will accelerate. So, with the same equation above, we can swap out the clutch for 10T instead and land on a gear ratio of 6:1 (60/10 = 6). This means that the kart will have a lower top speed but will accelerate faster out of the corners.
A lower gear ratio (referred to as a taller gear ratio in technical terms) will give you a higher top speed. On the other hand, a higher gear ratio (referred to as a shorter gear ratio in technical terms) will give you faster acceleration. The technical terms are opposite to what you might logically expect them to be, which is why it can be confusing.
In short, changing from a 12T clutch to a 10T clutch will give you lower top speeds but faster acceleration (shorter gearing). This will be the case as long as you’re not changing the sprocket on the rear axle. As soon as you change the rear sprocket, the gearing will change again.
3. Chain Compatibility
Another key difference between the 10T clutch and the 12T clutch is the chain that you will need to use. Because the number of teeth on the cogs of these clutches are different sizes, there are different distances (referred to as the pitch) between the teeth. The pitch determines which chain you should be using on your kart.
The 10T clutch needs a stronger chain, which is either a #40, #41, or a #420. These chains are more durable and less prone to breaking under the stress that they will be put through. On the other hand, if you’re using a 12T clutch, you’ll need a smaller and lighter, but weaker chain, which is the #35.
In general, if you have a lower gear ratio, you’ll need a bigger chain and vice versa. Keep in mind that if you change your rear axle sprocket as well, this will change your gear ratio, and at some point you may also need to change the chain when you’re using a rear sprocket with fewer teeth.
How Many Teeth Should My Go-Kart Clutch Have?
How many teeth your go-kart clutch should have depends on a variety of different factors. It all comes down to the setup that you’re using on your kart as to whether you should use a 10-tooth or 12-tooth clutch, and your rear sprocket will affect the decision too.
There are two different types of centrifugal clutches that you can attach to the drive shaft of your go-kart. There are more options out there, but the most common ones are the 10-tooth and the 12-tooth clutches. There are the clutches that perform the best in racing karts, and you’ll likely be choosing between these two.
It’s important to remember that you need to head out onto the track to do your own testing before deciding which one is better. As always, there is no right or wrong choice as there are many factors to consider.
Rear Axle Sprocket
Most drivers don’t mess around with the clutch too much. That’s because changing the sprocket on the rear axle of the kart can achieve the same effect in changing the gearing of the kart. So, the first change that you should be making is to the rear axle sprocket, rather than the clutch.
You may want to play around with different combinations to see what works best for you both in terms of lap times and in terms of how comfortable you feel in the kart. But, at the end of the day, the setup comes down to your personal preference, so don’t be afraid to experiment with different clutches and sprockets.
The Track
The track that you’re racing on affects which gearing you should use on your kart. Every race track is unique, so you will need to make adjustments based on the length of the straights and the acceleration you need out of the slower corners. Faster circuits with flowing corners, like Zuera in Spain, will require taller gearing.
However, circuits with tighter and twistier sections, like the Bahrain International Karting Circuit, may require shorter gear ratios to help you launch out of the corners faster. Gearing can be tricky to get right at first, but everyone usually ends up in the same range in terms of sprockets and clutches.
The Session You’re Participating In
The session that you’re taking part in may also impact the gearing that you set your kart up for. If you’re heading into qualifying and you need to set one flying lap, then having a shorter gear ratio could benefit you over just a single lap. For these sessions you could either bolt on the 10T clutch or a bigger sprocket on your rear axle.
But if you’re in a race and need to get some overtaking done, it’s more beneficial to have taller gearing. Taller gearing will give you a higher top speed at the end of the straight, making it easier to overtake other karts during a race. In this case, you would switch over to the 12T clutch, or a smaller sprocket on the rear axle.
Your Driving Style
Just like a fingerprint, every driver has a unique driving style. So, while everyone might be in the same ballpark in terms of gearing, the setup that works best for another driver might not work for you. That’s why it’s so crucial to do testing beforehand to understand which type of gearing suits your driving style best.
Some drivers are more aggressive and slide their kart around, which means that they would need more power and acceleration coming out of the corners (and thus shorter gearing). Smoother drivers can prevent scrubbing off speed through the corners, and they could benefit from having taller gearing as they keep the revs up coming out of the corners.
KEY POINTS
• Choosing between a 10-tooth and 12-tooth clutch depends on a variety of factors
• It will impact your gearing ratio and the performance of your kart
• You should test both to see which suits your driving style best
Testing To Find The Right Clutch
In the majority of cases, most drivers will only be adjusting the sprockets on the rear axle of the kart. When you start changing the clutches and sprockets around things can become a bit more complex as there is a chance that you could end up confused as to what the kart is doing after you’ve made the changes.
Before you go into an event, you need to make sure that you’ve done some testing of your own and you understand what effect your changes will have. This will give you more confidence going into a race weekend as you’ll know whether you need to change the clutch or the sprocket on the rear axle to get the change in performance that you need.
The general rule for gearing is straightforward, but there is still some wiggle room. Your gearing will be right if your kart hits the rev limiter for just a second or two before you hit the brakes at the end of the longest straight.
At the end of the longest straight, you need to be at maximum velocity (when your engine hits the rev limiter), meaning you don’t need your gearing to be any taller. From there you can make small adjustments and keep an eye on your lap times.
Final Thoughts
There are three key differences between the 10-tooth and the 12-tooth clutch. The most important difference is that they will change the gear ratios of your kart. The 10T clutch will give you shorter gear ratios (faster acceleration) while the 12T clutch will give you taller gearing (higher top speeds). Make sure to do some testing to see which one works best for you.
I created and have been writing on this site since 2019, collaborating with drivers, coaches, engineers and manufacturers to provide you with the most reliable information about motorsport. Find out more about me here.