Suspension Tuning-What comes first?

[DeltaV]

I've been interested in vehicle dynamics for quite some time, mostly on the design and R&D side, but I haven't really given much thought to the trackside tuning side until recently. Basically, I'm having trouble understanding how the concepts that have been discussed ad naseum on this board and others (weight transfer, roll centers, roll moments etc) actually translates into the real world. I've read enough Carol Smith to get the basics-car understeers, soften the front. Oversteers-soften the rear etc, but where i'm really having issues is deciding what to change based on driver feedback and data.

So lets imagine you are a race engineer for such and such race team. You are running two cars at a test at the Nurburgring GP track. One is an F3 car and the other is a Formula Ford (aero car and non aero car, respectively).

F3 hotshot driver comes in, throws on his massive sunglasses, and you ask him how the car feels. He says it's understeering here and there before he runs off to take some selfies and post them to Twitter. Data confirms understeer.

Formula Ford hotshot driver comes in, cleans off his gold Alpinestars race boots, and you ask him how the car feels. He says the thing is undrivable because it's oversteering everywhere. He then runs off to the press, saying how the car is a pig and how he is in talks with Ferrari for next season (he isn't). Data confirms oversteer.

So, what is your next step as race engineer? You have all of these adjustments at your disposal: alignment, corner weights, springs, bars, wings etc. Where do you start? What do you change first?

[fausto cedros]

It depends from the speed: are you looking for mechanical grip or aerodynamic grip?
It depends from the phase: corner in/out(transients) or steady state( first, dampers, second, bars/ springs,in both roll center movements have to be figured out).
By the way, always check tire pressures and temperatures first.
This is from my personal experience (Formula Renault 2.0, and CN Sport prototypes (Norma M20F Ohnlins equipped with three damping elements at the front, and Ligier Js51 with single spring at the front, Koni dampers).

[PhillipM]

Start by looking really busy, tell them you have a superb solution you've been wanting to try for that, don't change anything, and send them back out.

Marvel at the speed they gain.

[Jersey Tom]

What comes first is breaking it down, and also being aware of what knobs you can turn on your car. For example, you have some really powerful adjustment options if you have a ramp & clutch diff as opposed to an open diff.

Things to think about for a generic road course:

• You can break down high speed balance vs low speed balance to try and figure out if you need to work on aero vs. mechanical.
• You can break down steady state sweepers vs. transient.
• You can break down left handers vs. right handers.
• You can break down entry vs. exit or on- and off-throttle.

Splitting it up and knowing what car adjustment affects each specific area there is what would generally guide you, I'd say. You also take everything the driver says with a grain of salt. Sometimes they may not be telling you 100% of the story, and some things they say (or interpret) may not be correct at all.

Let's make up an arbitrary scenario. Let's say it's that Formula Ford guy bitching about oversteer everywhere. You look at the data and see yeah, there are places where he's counter correcting like hell. But.. then maybe you see those places are in esses or quick transients, and in slower steady state corners the car is understeering a good bit and he hadn't mentioned it. Then you look at your setup sheet and you've got the car pretty softly sprung.

So.. to cure his "oversteer" problem maybe you add rear spring (stiffness).. which seems counter-intuitive, but might both (a) give some better platform feel and keep the car from falling behind the drivers inputs in transients, and (b) frees up the balance in the steady state stuff. Then maybe you also tell the guy to try and slow down and smooth out his inputs.

Just an example. The order of stuff you go in will vary by person, by driver and what they like, by car, by track.

[DeltaV]

What comes first is breaking it down, and also being aware of what knobs you can turn on your car. For example, you have some really powerful adjustment options if you have a ramp & clutch diff as opposed to an open diff.

Things to think about for a generic road course:

• You can break down high speed balance vs low speed balance to try and figure out if you need to work on aero vs. mechanical.
• You can break down steady state sweepers vs. transient.
• You can break down left handers vs. right handers.
• You can break down entry vs. exit or on- and off-throttle.

Splitting it up and knowing what car adjustment affects each specific area there is what would generally guide you, I'd say. You also take everything the driver says with a grain of salt. Sometimes they may not be telling you 100% of the story, and some things they say (or interpret) may not be correct at all.

Let's make up an arbitrary scenario. Let's say it's that Formula Ford guy bitching about oversteer everywhere. You look at the data and see yeah, there are places where he's counter correcting like hell. But.. then maybe you see those places are in esses or quick transients, and in slower steady state corners the car is understeering a good bit and he hadn't mentioned it. Then you look at your setup sheet and you've got the car pretty softly sprung.

So.. to cure his "oversteer" problem maybe you add rear spring (stiffness).. which seems counter-intuitive, but might both (a) give some better platform feel and keep the car from falling behind the drivers inputs in transients, and (b) frees up the balance in the steady state stuff. Then maybe you also tell the guy to try and slow down and smooth out his inputs.

Just an example. The order of stuff you go in will vary by person, by driver and what they like, by car, by track.

Ah! Counterintuitive to say the least. Based on a "traditional" approach to the situation you described I would soften the rear bar to fight the transient oversteer, and soften the front to fight the stead state US.

What do you mean by "platform feel" and "frees up balance"?

Thanks!

[Jersey Tom]

Ah! Counterintuitive to say the least. Based on a "traditional" approach to the situation you described I would soften the rear bar to fight the transient oversteer, and soften the front to fight the stead state US.

What do you mean by "platform feel" and "frees up balance"?

Thanks!

"Freeing" a car up is synonymous with moving in the direction of less understeer. Just some parlance more common to.. other racing series. Platform feel is.. well.. how the sprung platform (the chassis suspended by the springs) feels.

Suffice to say, if racecar engineering was as simple as "understeer = soften front, oversteer = soften rear" then race engineers would be a dime a dozen. It's a vast topic, and one where experience and a good notebook go a long way.

Not to mention, how 'Engineer A' goes about solving 'Handling Problem X' may be completely different than how 'Engineer B' does it. For that matter I could ask - why would you reach for pulling rear spring (or ARB) if the driver is complaining of transient oversteer?

[DeltaV]

Ah! Counterintuitive to say the least. Based on a "traditional" approach to the situation you described I would soften the rear bar to fight the transient oversteer, and soften the front to fight the stead state US.

What do you mean by "platform feel" and "frees up balance"?

Thanks!

"Freeing" a car up is synonymous with moving in the direction of less understeer. Just some parlance more common to.. other racing series. Platform feel is.. well.. how the sprung platform (the chassis suspended by the springs) feels.

Suffice to say, if racecar engineering was as simple as "understeer = soften front, oversteer = soften rear" then race engineers would be a dime a dozen. It's a vast topic, and one where experience and a good notebook go a long way.

Not to mention, how 'Engineer A' goes about solving 'Handling Problem X' may be completely different than how 'Engineer B' does it. For that matter I could ask - why would you reach for pulling rear spring (or ARB) if the driver is complaining of transient oversteer?

Less rear bar would decrease the rear roll stiffness and thus reduce oversteer.

However I can see what you're saying about a softly sprung car having issues in the quick transients...we're seeing a high latency situation, correct? So the car FEELS like it's oversteering but in reality it's kind of just having issues changing direction. Is this what you're saying?