The compromises involved in delivering optimal F1 ride quality

The term ‘ride quality’ is more generally associated with luxury saloon cars than with Formula 1 machinery but, in its own way, it’s equally important to any form of competition car. To understand why, we first have to ask what we mean by ride quality.

Any vehicle travelling over bumps in a road will experience a vertical force as it traverses those bumps. Some of that force will deflect the tyre sidewall and some will be passed through the wheel to the suspension, where again some deflection will take place. Finally some force will act on the chassis and the driver.

The way the force is transmitted and absorbed by the tyres and the suspension depends on their stiffness, and the final effect on the chassis and driver depends on both these stiffnesses and the mass of the vehicle. If you drive behind a car towing a light two-wheel trailer that has no load, you will see it skipping and jumping over bumps in the road. When it has a load in it the vertical motion is much more controlled.

But why do we need good ride? It’s often perceived that a stiffly sprung car with heavy damping is very responsive and therefore more suited to sporty driving. In some respects this is true, but it comes at a cost.

If we consider that trailer again, if the bouncing is severe enough then the wheels may actually leave the ground. When they’re in the air they obviously aren’t gripping the road and, if this occurs in a corner, momentarily the trailer cannot negotiate the corner.

In fact it’s the variable load the trailer has to deal with which explains part of the reason that getting a good ride quality is difficult in a racing car. The spring stiffness of the trailer has to be designed to support the load of the full trailer. An F1 car will have to deal with some variation of mass between a full and empty fuel tank but this is only around 15% of the weight. This is roughly equivalent to the difference in a small road car between having just the driver in the car or adding three passengers.

The current generation of ground effect F1 cars are set-up to run low to the ground

Photo by: Glenn Dunbar / Motorsport Images

Much more significant is the huge aerodynamic forces the car can generate, and which have to be fed through the suspension to the road. If the F1 car springs were soft enough to give a smooth ride then these enormous loads would grind the car into the ground at high speed.

A further complication is that with an F1 car we need to provide a stable aerodynamic platform. What this means is that the car will produce its best downforce when it is at a certain height from the ground, known as the rideheight.

Ideally we would like the car at this height no matter what loads are imposed on it, and this was one of the objectives of active suspension. However to achieve this with a passive arrangement we need to have stiff suspension which, just like the bouncing trailer, will reduce our tyre grip – particularly in slow corners when we don’t have so much aerodynamic load.

If the aerodynamics of the car are such that it’s not particularly sensitive to ride heights then it could be sprung relatively softly. If the aerodynamics dictate the car needs to be held close to the ground, then it will need stiff springs

So how do we achieve a reasonable compromise? The answer lies in simulation and testing on sophisticated ride rigs.

It’s not difficult to simulate on a computer the ride qualities of the car. A mathematical model is programmed and virtual vertical inputs are made at the tyre. The model will then compute the variation in vertical tyre force and chassis deflection. These inputs can be done for different frequencies and the outputs examined. The response of both the wheel and the chassis are then plotted against frequency in what is known as a Bode plot.

Now every system like this will have natural frequencies. For each part that can move independently of another, a natural frequency will exist. So in our complete car we have frequencies associated with pure bounce, with pitch and with roll as well as a frequency of the wheel itself bouncing, which is known as wheel hop. There are many other natural frequencies but they aren’t quite so relevant to ride.

The two most important frequencies on an F1 car are the bounce and pitch frequencies. These will determine the control of the vertical tyre forces and the stability of the body in the sense of providing a stable aerodynamic platform.

Active suspension systems were used to ensure F1 cars ran at the optimal rideheight all around the lap, but were banned for 1994

Photo by: Motorsport Images

Unfortunately, with a passive suspension system and particularly with one that has to carry a variable load, it’s difficult to tame these frequencies. So, as with all engineering design, compromises have to be made.

The testing will yield what are known as transfer functions. These are measures of the variation in wheel load or body position. Most teams will have developed a ride quality index to balance these transfer functions to give the best trade-off of the conflicting requirements, allowing them to tune their spring and damper settings for best performance.

This ride quality index isn’t a magic number, however. Different aerodynamic characteristics and indeed track roughness will affect behaviour. If the aerodynamics of the car are such that it’s not particularly sensitive to rideheights then it could be sprung relatively softly. If the aerodynamics dictate the car needs to be held close to the ground, then it will need stiff springs.

While all F1 cars since the advent of underbody aerodynamics have tended towards the latter, the current regulations, which very much rely on ground effect, have dictated extremely stiff suspension set-ups. Consequently the ride is harsh and the variation in vertical load at the tyre contact patch is more extreme than the vehicle dynamics engineers, and drivers, would like.

This manifests itself in poor grip in low-speed, bumpy corners and a harsh environment for the driver. Like many other engineering decisions it comes down to compromise and redefining that ride quality index to minimise the most important parameter in motorsport – lap time.

As teams have pursued optimal lap time in the face of porpoising, riders' comfort has been compromised

Photo by: Steve Etherington / Motorsport Images