Thoughts (or preexisting studies) on delay in load transfer due to softer springs?

[harshsr]

Talking about lateral acceleration, I know that roll stiffness or spring stiffness doesn't affect how much load is transferred from inside to outside of the vehicle. But would having softer springs create a delay between the moment the sprung mass experiences lateral acceleration and the moment springs are in equilibrium and the tyres are reacting to the load transfer?
If so, what kind of effect does this have on the overall cornering performance in say, a high lateral acceleration corner?

[Stu]

The advent of complex damping control (low-speed/high-speed adjustments and ‘blow-off’ valves) was a game-changer for this. Teams went from fitting the (very) stiff springs required to control the aero platform (with very basic damping) to using low speed damping to control the platform with softer springs fitted (which worked with high-speed damping) to control individual wheel movements. And kerb-hopping became a thing….

Williams famously ran an FW08 (I think) with ‘solid’ suspension at a Silverstone test - because the springs were so stiff, they thought “why not”!!
In the same period they also ran the wind-tunnel model without drive-shafts “to see what the effect was”!!

[Greg Locock]

There is a fairly interesting plot in RCVD which shows how the forces build up in various suspension components as the car enters a turn.

It is, I suppose trivially obvious that if you change the understeer by retrimming the springs front to rear then you'll change the yaw delay time due to the different load transfer speeds.

So if you increase the roll stiffness at the rear (and reduce it at the front to keep the same roll gradient), you'll increase the absolute rear cornering compliance (understeer =FCC-RCC) and the yaw delay time should drop.

At peak cornering yes, the front to rear balance will change the maximum grip of each axle, due to https://en.wikipedia.org/wiki/Tire_load_sensitivity

generally the more equally you can weight the tires on each axle the higher the combined grip of the axle will be.

[Greg Locock]

And, if you have tire curves, the calculation of max lat acc is a simple spreadsheet model. Getting the individual wheel loads, vertically, is probably the hardest bit. bear in mind that for max latacc you want each axle to react its proportion of the mass of the car, while the downforce may not be distributed in the same proportion.

[harshsr]

bear in mind that for max latacc you want each axle to react its proportion of the mass of the car, while the downforce may not be distributed in the same proportion.

Wouldn't it be more desirable for each tyre to be loaded equally for maximum latacc? Theoretically speaking of course.

[Greg Locock]

Not if the tires aren't the same all round, or the weight or aero distribution isn't 50/50 etc. But since the cg is always above ground the outside tires are always more heavily laden, so its a question of deciding which end is going to see the most load transfer. Usually it's the fronts for two reasons - it gives you understeer, and with rear wheel drive it gives you better traction.

You do need to know the roll centre heights.

You can do all this roll moment distribution stuff in a spreadsheet model, I think Gillespie outlines a method. Alternatively Dynatune http://www.dynatune-xl.com/ has done all the hard work.

People sometimes talk about lateral load transfer distribution (LLTD) rather than roll moment distribution (RMD), I'm not so bored that feel like checking if they are the same.

[henry]

Thinking crudely I have a vision of 2 states of the suspension in roll. One the steady state with the load distribution dependant on springs only, and the other transient, dependant on the springs and dampers. The higher the roll rate the higher the damper contribution.

I think this might mean that the tendency to understeer or oversteer might be different in transient and steady states. And it might be possible that different driving styles might result in differences in the relationship between these two states. An “aggressive” driver, very high rate of turn in, may see more contribution from dampers than a smooth style.

[Greg Locock]

The fastest build up in forces is the mechanical path, ie roll centre heights, then the shocks, followed by springs and a/r bars.

[godlameroso]

The fastest build up in forces is the mechanical path, ie roll centre heights, then the shocks, followed by springs and a/r bars.

Can ARBs affect the damper histogram? Like for example, if I see the right side more biased on compression, and left side more biased on rebound, could running more roll stiffness bring the histogram into symmetry?

The alternative would be to fix the asymmetry with asymmetrical damper settings, which I would tend to avoid.

[Greg Locock]

I think it will depend on the cause of the asymmetry - is it weight bias in the car, corner bias in the track, or what? I've never used histograms as any attempt to introduce deliberate asymmetry into a mass production car, whether in components (particularly) or hardpoints, would be greeted with howls of protest. We get away with cross castor.

[Tim.Wright]

The fastest build up in forces is the mechanical path, ie roll centre heights, then the shocks, followed by springs and a/r bars.

Can ARBs affect the damper histogram? Like for example, if I see the right side more biased on compression, and left side more biased on rebound, could running more roll stiffness bring the histogram into symmetry?

The alternative would be to fix the asymmetry with asymmetrical damper settings, which I would tend to avoid.

ARB's act symetrically so that won't shift your histogram.

Asymmetric damping curves are commonly implemented on CPL reduction grounds.

[Greg Locock]

I had a sneaking suspicion they wouldn't help in general, but suppose you've got one hot tire at one end, wouldn't more bar at the other end reduce the load on the hot tire? - answering my own question, yes, but symmetrically.

[godlameroso]

I had a sneaking suspicion they wouldn't help in general, but suppose you've got one hot tire at one end, wouldn't more bar at the other end reduce the load on the hot tire? - answering my own question, yes, but symmetrically.

Depends, if the roll rate is too high the tire has less grip, more slip, more surface temp. More load on the tire tends to heat the carcass itself. So while you are loading the tire less, you can still increase surface temps, and eventually the core will act as a heat sink for the surface.

Then you have to ask if indeed, roll rates and damping rates play hand in hand, as both can be used to control the timing of weight transfer. If you bias your dampers on rebound, you are delaying the extension of the inside wheel, just like a roll bar would. Then the ratio between the wheel rate roll rate and the damping rate affects all of this. Mechanical grip for instance could be the solution for a hot tire, because if the car is a bit more pointy you can use a bit less steering lock in the parts that really heat the tires.