In the opinion of many in racing, soft springs make more grip by allowing the suspension to follow the undulations in the road.
Our experience at Racing Car Technology, over nearly twenty years of setting up race cars is very different.
Our number #1 priority for Suspension Tuning, is that we need stiff suspension to make grip at the tyres. Yet the counter argument, that we need soft springs for grip, is out there, and etched into our thinking. Faced with a handling problem, anyone of us might backslide into the old ideas.
Let’s be clear about this – if we have springs that give the stiff suspension frequencies we recommend for racing – there will be no magic softer spring we can fit, that will suddenly make more grip.
Proponents of the “soft springs for grip” scenario, suggest that the better handling you get with stiffer springs comes only from the improved car response – ie driver feel, speed of response, less variation of critical suspension angles – toe, camber, caster.
They're saying you run the car as soft as possible - just enough to keep the car from bottoming out and then only increase spring stiffness marginally from there. (Carroll Smith in his book, "Tune to Win", expressed this view.)
But it is only a small part of the story.
As you increase suspension stiffness from soft road suspension stiffness, the gains you get with improved car response will flatten out. Yet, we keep on making more grip at the tyres with increasing suspension stiffness, up to the level of stiffness that you need for racing.
Here’s two strong arguments, demonstrating that you need stiff suspension to make grip at the tyres. In neither case, can the car response be that much of an influence.
Firstly, the 7-post rig. If the soft spring rule was true, we’d make grip with soft springs and shocks. This is not the case. We make grip with stiff springs to help key the rubber into the road surface and soft shocks in the high-speed range, so as not to interfere with the high speed micro vibration at the tyre contact patch. (Teams may well run with stiffer shocks than suggested on the 7 Post for reasons of stability, but the spring recommendation should be pretty much a no-brainer.
Secondly, what’s the easiest way to make big gains in grip on the 300 ft skid pad (as used for lateral G testing)? Just bump up the spring rates from standard – a lot. You can have a bread and butter FWD Toyota gripping up like a Porsche.
Road Performance: Stiffer springs, without overly compromising ride quality.
Through to.....(all in between uses, such as tarmac rally). Stiffer springs again.
Racing: Much Stiffer springs for Maximum Grip. Ride doesn't count.
In our online training course, "Get More Grip and Better Balance", we show you exactly what suspension stiffness you need for your use of your race or road performance car.
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