Every single part of how a vehicle performs, from cornering speed and rigidity through to braking and acceleration, can be attributed to the grip the vehicle’s tyres have on the road. A huge portion of the complicated suspension components within modern cars are there to ensure that all 4 wheels stay firmly planted on the ground with the weight firmly distributed across all 4.
A vehicle is only as good as its connection to the road. A car with cheap, poor quality tyres that don’t grip, will be easily outperformed by an identical vehicle with high quality tyres. It’s the same, although much more extreme, when a vehicle is being driven on snow and ice – grip is everything.
If you’re interested in performance motor vehicles and shows, you may have noticed the terms 40/60 or 50/50 in relation to vehicle weight distribution. Now, you may be aware that these indicate the percentage of the vehicles weight over the front and rear wheels, but are you aware of how different set-ups affect a vehicles handling?
Here are some of the basics of vehicle physics.
As a vehicle is braking into a corner, there is less weight over the rear wheels (all of the weight has shifted forward). This has the potential of causing the rear end to lose traction. This reduces the effectiveness of the rear brakes (it can’t brake if it can’t grip the road) and could cause the rear of the vehicle to slide outward during cornering.
Conversely, as a vehicle accelerates, the weight travels to the rear of the vehicle, reducing the grip of the wheels in the front. This will reduce the vehicle's ability to steer as it accelerates out of a corner, or completely remove its ability to accelerate (in the case of a front wheel drive vehicle).
This is where proper vehicle weight distribution comes in.
A vehicle that has a weight distribution biased towards the rear of the vehicle (40/60) can brake later and harder into corners. This is because as the vehicle brakes, the weight moves towards the front of the vehicle and the vehicle gets closer to a 50/50 weight distribution. All the tyres now have an equal grip on the ground and can brake evenly. This is why most 'performance' cars are rear-engined, as it's the heaviest part of a car.
However, when a vehicle like this begins to accelerate out of the corner, the weight will bias even more to the rear, allowing the vehicle to accelerate harder (more weight over the rear wheels) but leaves less grip for the wheels that steer. This is not an issue for vehicles that only need to travel in a straight line; drag cars for instance, put the majority of the weight over the rear wheels so that they have the most traction off the line.
The positive and negative benefits of the different kinds of car weight distribution are heavily contested between experts. The set-up of a vehicle is largely dependent on the kind of driving the vehicle will be doing and the driving style of the driver. A drift vehicle is set up very differently to a Formula 1 vehicle, and each is very different to a 'normal' road car.
How do car makers and engineers work out the weight distribution in cars? They use devices called corner weight scales, otherwise called axle weigh pads. These are individual scales that sit underneath each tyre and weigh the individual corner weight; this is then calculated into overall weight and weight distribution, helping the engineers calculate the correct physics of the car and its handling.