Demystifying the complexities of racing car spring tuning is essential for a fast car setup. Yes, it can feel complicated. Consequently, many within the motorsports community rely on experience, empirical methods, or paddock whispers to choose the “right” spring settings. Some people even choose suspension systems based solely on brand names, without considering the necessary specifications. This lack of understanding about suspension tuning is clearly frustrating for anyone who’s ever asked, “What springs should I run on my racing car?”
In this article, I will help you explore the key challenges in racing car spring tuning. I will then offer two simple strategies involved in achieving the “optimal” spring tuning for your track or racing car. If you’re used to traditional methods, the suggestions might come as a surprise. If that’s you, then I sincerely hope this helps you, as it did for me the first time I discovered these methods.
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The Complexity of Racing Car Spring Tuning
One of the primary challenges in suspension tuning is the fact that a most peoples car’s suspension must handle various situations or modes with only one setting.
For example, the same set of springs is used to manage bumps on the road and to control the car’s balance through corners.
While advanced components like third springs and inerters can help optimise suspension for different modes, most readers of this article will likely face these more typical compromises in their suspension settings.
Achieving the perfect setup for every mode is not feasible, so you need to know what compromises you’re making.
Defining Success in Racing Car Suspension Tuning
Measuring success in suspension tuning is not as straightforward as one might think.
While it’s tempting to assume that racing drivers simply desire more grip, measuring grip on a racing car is challenging.
This measurement is almost impossible to obtain on an actual car at a track, where most readers would be assessing their tuning success.
Grip comes from your tyre’s contact with the road.
Unfortunately racing drivers can only sense the lower part of the vertical frequency range through which grip is generated – things like big bumps or at the onset of braking and cornering events.
The higher frequency stuff is what is happening at a resonant level at the contact patch.
Arguably it has a bigger impact on the available grip and typically falls into the “ride” side of vehicle dynamics tuning.
Some F1 suspension gurus I’ve worked with have even gone so far as to say:
“Drivers have no understanding of Ride. None. Absolutely zero. And I am talking about the World Championship-level drivers I have race engineered.”F1 Race Engineer – Anon
This limited sensory range adds further complexity to the suspension and spring tuning process.
Recognising the Interconnectedness of the Front and Rear of the Car
Although it may seem obvious, it’s crucial to understand that the front and rear of the car are connected.
Unfortunately, most suspension and spring tuning approaches treat the front and rear as separate entities, simplifying the mathematical calculations.
A typical approach is to utilise suspension ride frequencies to specify the spring rates.
Here you can see a table of the typical values people suggest:
|Car Type||Typical Ride Frequency|
|Road Car||1.1 – 1.3 Hz|
|Sports Car||1.3 – 1.7 Hz|
|Super Car||1.7 – 2.2 Hz|
|Race Car||2.0 – 2.8 Hz|
|Formula Car||> 3.0 Hz|
In theory, you simply pick your car type and, with some basic maths, have your spring rates.
The conventional wisdom then suggests that the rear ride frequency should be higher than the front.
This is because the front hits the bump firsts, so having a higher rear ride frequency allows the rear suspension to “catch up” with the front after encountering said bump.
This approach aims to achieve what Maurice Olley described as a “flat car” scenario in the 1930s.
While this is a reasonable starting point, there is room for improvement because it’s not clear, to me anyway, why a race car has to have those frequencies, or by how much the rear needs to be stiffer than the front (if at all).
Typical figures suggest about 10% higher for the rear than front – but why?
Let’s take a step back.
The Fundamental Principle: “Tyres Don’t Like Surprises”
Throughout the process of racing car spring tuning, it is essential to remember the fundamental principle: “Tyres don’t like surprises.”
Surprises, in this context, refer to shock loads that adversely affect the tyre’s grip on the road (you can learn all about tyres here.)
Running out of suspension travel can result in shock loads that disrupt the weight distribution across the car.
This scenario can lead to non-linear behaviour in handling or, in extreme cases, loss of control.
Hence, it is crucial to maintain a clear understanding of this principle when tuning springs to achieve optimal performance and handling balance.
With that in mind:
Two Simple Steps for Selecting Your Ideal Spring Rates
1. Use All Your Available Wheel Travel
First and foremost, consider the amount of wheel travel available in your car.
Yes that’s right, your wheel travel – it got me too first time!
The purpose of suspension with springs is to absorb road inputs and facilitate controlled load transfer between the four wheels.
Running out of suspension travel is the last thing you want to happen because it can create shocks to the tyres, potentially leading to loss of grip. See comment above about Tyres not liking surprises…
Additionally, running out of wheel travel can alter the car’s handling balance, especially at critical moments like mid-corner.
Determine your car’s working range of wheel travel, aiming for as much travel as possible without running out.
Calculating scenarios where the wheel travel will be tested at its maximum, such as during straight-line braking at threshold, can help inform your decision.
You can estimate this using moments from your centre of gravity height, your wheel rates and your motion ratios to estimate load transfer and suspension travel change.
It’s not difficult but in my Tuning for Traction workshop I include a spreadsheet that does this for you.
2. Seperate Pitch and Heave Centres
Understanding “pitch” and “heave” centres is crucial in achieving a more controlled difference in front and rear spring stiffness.
When you connect the front and rear suspension in a simplified model and press down on the car, it will exhibit both pitching and heaving motions.
Each of these modes has a centre, a point where pressing down will induce only pitching or heaving motion.
These motion centres’ positions depend on the natural frequencies of the front and rear suspension.
To optimise spring tuning, aim for the pitch centre to be around the front axle and the heave centre to be outside the wheelbase.
This setup helps achieve a flatter car response and instils confidence in the driver when encountering obstacles.
Again you can workout the precise distance of these pitch and heave centres relative to your centre of gravity. This is also included in the Tuning for Traction Excel tool.
Racing Car Spring Tuning: In Summary
Demystifying the complexities of racing car spring tuning is essential for achieving a fast car setup.
From debunking common misconceptions to comprehending the intricacies of suspension tuning, this guide aims to help you see through the “paddock folklore” surrounding this subject.
Yes, it is complicated, but by understanding the interconnectedness of front and rear suspensions and adhering to the principle that “tyres don’t like surprises,” you now have a more solid foundation for selecting the springs that will work.
By utilising your car’s available wheel travel and properly identifying pitch and heave centres, you can create a more controlled management of the load distribution around your car.
This guide is a first stepping stone to at least point you in the right direction for how to go about doing this.
Follow these suggestions, and then you will invariably need to start tuning your front anti-roll bar stiffness.
This is because the flat ride and split pitch and heave centre approaches leave you with more stiffness on the rear.
In a corner, this means the rear will likely saturate first, leaving you with an oversteering or nervous-feeling car.
As the anti-roll bar is normally one of the easiest adjustments to make, hopefully, you’ll soon be well on your way.
That then just leaves dampers…
For many of the same reasons that springs are doing more than one job, dampers become complicated to tune too.
I will, therefore, leave dampers for another day and hope that at least you now have good clarity and reasoning behind what springs to choose and why.
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