Power-to-weight ratio is something that is often talked about in the automotive industry. It is essentially a way of describing how fast your car is. It’s an important performance factor in car racing, which leaves many wondering if the power-to-weight ratio is important in go-karting.
Power-to-weight ratio is critical for a go-kart. This element is the sole reason karts can go as fast as they do with such small engines. Kart engines offer relatively small amounts of horsepower, but thanks to the minimal weight of the vehicle, they can still go incredibly fast.
There are some great benefits to having such a high power-to-weight ratio, such as faster acceleration, better top speed, and more responsive handling. Overall, these factors are what makes go-karts so fast and so fun to drive, but let’s look at the power-to-weight ratio in more detail.
What Is Power-To-Weight Ratio?
Power-to-weight ratio is a performance measurement used to indicate how fast a vehicle can travel. Generally, the higher the power-to-weight ratio, the faster the vehicle will go. In order to calculate this ratio, you simply need to divide the power of the vehicle by its total weight.
For example, if you have a car that weighs 1500 kg and it has a power output of 300 HP, the power-to-weight calculation will be as follows:
300 / 1500 = 0.2
Remember, the higher the number, the better (in terms of speed). When that number gets to 1.0, you have a car that has power equivalent to its weight. The first road legal, production car to have an equal power-to-weight ratio was the Koenigsegg One:1. That means that this car has 1 horsepower for every kilogram of car. In other words, the One:1 weighs 1360 kg and has 1360 horsepower.
However, the ratio can be used in different ways depending on the units you use. In the case of the One:1, it works when you use kg and BHP, but not when you use lb and BHP (1360 BHP : 2998 lbs = 0.45). So, for the sake of this article, we’ll stick to kilograms (kg) for weight and brake horsepower (BHP) for power.
Racing cars such as F1 cars and dragsters all have a power-to-weight ratio over 1.0, which is what makes them so incredibly fast. Here are some of the power-to-weight ratios of well-known supercars (horsepower per kilogram):
Ariel Atom – 0.909
Ferrari LaFerrari – 0.76
Bugatti Chiron – 0.758
Pagani Huayra – 0.65
McLaren P1 – 0.593
Lamborghini Aventador – 0.463
What Is The Power-To-Weight Ratio Of A Go-Kart?
Go-karts are incredibly light. So much so, that the weight of the driver can make a huge difference to the overall power-to-weight ratio of the vehicle. In addition, there are different engines with varying power outputs.
To keep it simple, we will be looking at Rotax engines and taking regulation minimum weights (for racing) in order to calculate our kart power-to-weight ratios.
A senior max Rotax kart produces around 30 horsepower. The global Rotax regulations state that senior class minimum weight is 160kg. This includes the kart, driver, and all safety gear. In other words, this is the fastest possible (race legal) setup we can work with.
Based on this, we can work out the power-to-weight ratio of a Senior class Rotax Max kart to be:
30 BHP / 160 kg = 0.1875
We can multiply this number by 1000 to get horsepower/ton = 187.5 BHP/ton. Considering that a kart only weighs 160kg, this amount of power is relatively large.
But, if that isn’t enough for you, you can always opt for a KZ shifter kart. These karts can produce up to 50 horsepower and weigh 160kg. This makes the power-to-weight ratio 0.3125, or 312.5 horsepower per ton. A mere 20 extra horsepower makes an enormous difference in a small, lightweight go kart.
Is Power-To-Weight Ratio Important In Karting?
Go-karts are extremely lightweight vehicles. Without the driver, a kart can easily weigh under 100kg. Usually, the driver is the heaviest part of the kart, and therefore acts as the center of gravity. This yields a number of benefits.
Power-to-weight ratios are crucial in karting. Let’s calculate the power-to-weight ratio of two different karts to demonstrate just how crucial this performance element is in the sport.
A Comparison
Let’s say the first kart has a driver that weighs only 60kg. The total weight of their kart is 160kg and the Rotax Max engine can produce 30 horsepower. This gives us a power to weight ratio of 187.5 horsepower per ton. This is slightly more than that of a Mini Cooper S, which is quite impressive.
But now let’s compare that to a driver that is slightly heavier, weighing 80kg. The exact same kart that can produce 30 horsepower now weighs a total of 180kg. The power-to-weight ratio now drops down to 166 horsepower per ton. This is slightly more than a Mazda MX-5.
Essentially, by adding just 20 kilograms to the kart, it has lost 21.5 horsepower per ton. This shows just how impactful the overall weight of the kart is on its performance. This is exactly why there are minimum weight restrictions in place. Less weight on the kart equates to a massive increase in performance and lap times.
How Does Power-To-Weight Ratio In Karting Compare To Cars?
The power-to-weight ratio of a go-kart is incredible. If you compare standard Rotax Max senior class karts to cars you will find that it ranks quite highly in terms of its power-to-weight ratio. Here are some cars that the Rotax Max can beat in that division (units in horsepower per ton):
Rotax Max Senior Class – 187.5
Mercedes A Class AMG – 147
Mazda MX-5 – 134
Golf GTI – 129
Ford Fiesta ST – 125
Mini cooper S -117
When we take a step up and look at a KZ kart the numbers become even more impressive. These engines can produce up to 50 horsepower and the karts weigh a total of 170kg, giving them higher power-to-weight ratios than some BMWs and Audis.
KZ Class Kart – 294
BMW M3 – 289
Audi RS5 – 268
How To Use Weight To Your Advantage In Kart Setups
Utilizing the weight on the kart is crucial to your success in karting. Some lighter drivers may need to add extra weight to their karts in order to pass scrutineering. Make sure you balance your weights equally to prevent upsetting the kart.
Try to put a little bit of extra weight on the side opposite to the engine to counter that extra weight. Using your bodyweight is also crucial here. You can adjust the height and angle of the seat to change how the kart handles.
Maximizing Grip
It’s also helpful to move your body in the kart to maximize the grip where you want it. For example, pushing against the steering wheel will force you further into the seat. This will put more weight over the rear tires. Use this tip when you need some extra braking force or more traction out of corners.
In racing conditions, your weight will be taken as soon as you come off the track. If you are below the regulation weight you will be disqualified. With that being said, you need to get as close to that regulation weight as you possibly can. This means you need to do some testing and perform some calculations.
Measure Your Fuel Usage
It’s best to set a day apart and test your fuel usage and see how it affects your weight. Make sure that if your kart is empty on fuel, it weighs exactly on the limit. This way you can’t get it wrong on race day and face disqualification even if you have next to no fuel left. You also need to measure how much fuel your kart uses per lap (this of course varies from circuit to circuit).
Let’s take an example, saying you fuel up your kart for the duration of the race (let’s say 15 laps) plus 1 formation lap and 1 cool down lap. So, you would have a total of 17 laps of fuel onboard, which should be enough for the full race.
However, if you have an aborted start and need to do an extra formation lap for example, you will be one lap short on fuel. This means you may have to lift and coast to save fuel during the race, or just hope for the best and get to pit lane as soon as you can on the cool down lap.
How To Drive Against Lighter Drivers
There may be rules in place to equalize the weights across all karts in a given race, but sometimes you may be just slightly heavier than the other guys on the grid. This is not necessarily a bad thing. You will need to work harder to beat them, but it’s all about skill and using that extra weight correctly. Let’s discuss how you can beat lighter drivers in a go-kart.
Drive Smoothly
Go-karts are all about keeping the revs as high as possible. They already struggle to accelerate as it is (especially rental karts) and adding extra weight will also add to that struggle. But if you keep your steering, braking and throttle use as smooth as possible, you can minimize the losses due to the extra weight. Squeeze the throttle slowly, keep the traction under control and the revs high.
On the brakes, use your body to kick the back of the kart out (opposite to the corner’s direction). Once you have the nose pointed at the apex get on the throttle smoothly. Using your body to brake allows you to brake harder and later.
Steering
Try to minimize your steering angle through corners. You want the kart to almost glide through corners rather than turning the wheel. It’s almost as if the kart is drifting with the steering wheel straight. When you get your braking technique right this will happen automatically.
Use all of these techniques together for a smooth and flowing cornering technique that will keep your speed high and your lap times low.
Keep The Revs Up
Keeping the revs high at all times is crucial to being fast in a kart. The lower the revs go the slower the kart is. It takes a relatively long time to build the revs back up, so try to keep the engine spooled up through the corners. If you’re smooth on the throttle it’ll be easy to keep the kart under control at high revs through the corners.
Perfect Your Racing Lines
If you’re on the heavier side in a karting race you need to have the perfect racing line. The perfect racing line is the fastest way around the track. This line will have the most grip and the best cornering angles.
If you are able to perfect the racing line you will save a lot on your overall lap times. Use your racing line with the cornering techniques mentioned previously and you can easily beat other drivers, even if they are a couple of kilos lighter than you are.
Final Thoughts
Power-to-weight ratios are key in karting. Every bit of extra weight added onto the kart makes a huge difference. It’s crucial to run as light of a kart as you legally can to increase your speed. The power-to-weight ratio of a kart is one of its strongest features, and when compared to other vehicles it’s up there with the likes of high-performance hatchbacks and sedans!
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