Don't believe road testers' fixations on body pitch and roll

Some body pitch and roll is essential for mechanical grip in slow corners. Photo: Shutterstock.
Some body pitch and roll is essential for mechanical grip in slow corners. Photo: Shutterstock.

Springs and anti-roll bars (and the dampers working with them) are a rather misunderstood aspect of suspension setup. It's also an issue that I reckon we can at least partly blame on road test writers and presenters.

The perception is that stiffer springs and sway bars must be better because of less pitch and roll, when it just isn't that simple.

Soft and stiff are also quite relative terms. What a race car considers soft will still be very firm in a road vehicle.

Stiffer springs and bars only perform better in specific circumstances, when the road itself is perfectly smooth and the vehicle has epic levels of downforce activated. This is because there are no bumps to upset the chassis, and the vehicle's height and rake (how much higher the back is) are important to achieve aerodynamic performance.

The problem is, even on those vehicles, the mechanical grip - the level of grip available at speeds below which downforce is inactive and thus influenced only by the suspension, tyres and road - is still compromised.

'But there is such a thing as too soft' I can hear some of you screaming inside your own heads. Yep, sure, but I'd argue it hasn't really been a problem in road cars for decades.

Meanwhile those who need to carry a heavy payload also know that too soft a spring rate means they just collapse under the weight (one reason that leaf springs always had an advantage over coil springs in light commercial applications).

In terms of handling though, this false belief in 'the stiffer the better' is one reason why it's possible to separate that concept of handling from the concept of performance. In this regard, handling could be defined as how it feels and how predictably (or perhaps more importantly, consistently) it behaves, whereas performance is how well it does when this behaviour is actually measured (by time, minimum or average speed, distance, or a combination).

Stiffer will feel better because of a slightly more eager initial response when you first move the controls. After that though, the grip available can tell a different story.

I'll also happily concede that softer still feels weird mid-corner and on corner exit, but that's because of two things. In my case, I got used to low and firm before learning that it wasn't optimal for lap times, and because there's also more going on when the suspension is allowed to move more.

Anyway, firmer suspension allows you to feel the loss of traction more sharply, so you feel more in control. The vehicle also feels fastest when it's on the edge of grip; the slip angle of the tyres is activated and you're having to manage the oversteer or understeer. It certainly gets your attention and your heart rate up on the track (especially when there are things at the track edge to hit like there are at most of the hillclimb events I've done).

We can think about our old friend load transfer when we talk about suspension stiffness, but framing it in those terms initially suggests you should get more grip because of a greater downwards push on the tyre you need the most grip from. The problem is, that's not all that happens.

One of those other things happening is there's more lateral and/or longitudinal load also being transferred to that tyre when the body isn't allowed to pitch or roll. That extra force forwards, backwards or sideways exceeds the additional downward force, so the tyre doesn't gain as much grip from load transfer as it needs to in order to deal with the excessive fore, aft or sideways load.

Too much pitch or roll is certainly a bad thing, but up to a certain point allowing some of the energy to go into that pitch or roll reduces the longitudinal or lateral forces so that the tyre doesn't have to hold on as hard.

Drag racers have long known that softer rear suspension allows them to launch a rear-wheel-drive harder from a standing start. That energy explanation is why. It's also why road testers fixating on a car that corners flat (ie. without much perceptible roll) is inherently the wrong characteristic to look for.

The same principle applies under braking. Springs that are too stiff make the tyres more likely to give up and stop turning. And if you're setting a car up for grip in the wet, you always go with softer springs and sway bar settings to get more mechanical grip.

This story Don't believe road testers when it comes to body pitch and roll first appeared on The Canberra Times.