Chassis - Suspension question

[George-Jung]

I have a few questions regarding "the perfect" chassis/suspension setup regarding:
- Spring rates
- Slow/Fast bumps
- Slow/Fast rebounds
- Sway bars


If we may persume that the spring rates of an imaginary race car are set to "the perfect" conditions and we also have "perfect" balance, should you than setup:

- the slow bumps to the highest possible setting to have maximum turn in, because of maximum input response?
- the slow rebounds to the highest possible setting to have the least amount- most controlled front to end body roll?
- the fast bumps to the lowest possible setting to have maximum mid- corner exit traction? Due to high slow bumps settings for high input response, you need soft fast bumps to gain wheel load while cornering?
- the fast rebounds set to the lowest possible setting to have maximum wheel contact with the track under bumpy conditions (kerbs etc)?
- the sway bars to the lowest possible setting to gain maximum wheel load while cornering, to compensate for the stiffest possible slow bumps setting?


*)highest/lowest possible settings within the tollerance limits of the materials.

I would love to hear from the experts, because I am not even an amateur.

[Greg Locock]

I am not an expert either.

But if an expert responds with any answer other than "It depends" then I will tease them mercilessly.

[J.A.W.]

Surely the "perfect" suspension-chassis would be AI controlled, with active responses pre-programmed..
..& be accurately reading the ground ahead & comparing it with file data.. providing millisecond adjustment..

Of course you may have to wait for the "AI Singularity" event, & hope that like ol' Adolf before them, our
new overlords are 'motorheads' with an interest in such things, as well as deeming you to be a "keeper",
& not a "useless mouth"...

Guess we'll all just have to await the event now then huh...

Edit: Hey, some humourless/ignorant sod just applied an anonymous downvote!
I hope whoever did that realizes - that automatically puts 'im on the post-singularity robo-puters - to do list...

Edit 2: Cheers to whoever gave me an upvote to cancel out the - ve one noted, stat above..

[George-Jung]

Thanks for your replies, but no expert yet..?

[Greg Locock]

Well maybe you didn't get the hint

There is no perfect spring setup independent of the perfect geometry and the perfect sta bars and the perfect tire pressures and the perfect shock settings and the perfect corner weights and the perfect jounce bumper clearances etc etc, for one lap of one particular track.

[DaveW]

......

& don't forget the damper design & (last but not least) the nut behind the wheel...

[Roni]

Not an expert here but i believe that the best solution is finding a priority list in what matters the most.
In my view the priority list looks something like this:
1) Front and Rear springs and sway bars/ anti roll bars (mechanical grip)
2) aerodynamic grip related tuning (in any)
3) differential settings
4) damper settings (a bit enhanced mechanical grip)
I think someone or the other might take at dig at me for putting damper settings at the bottom of my list, but hear me out.
Springs are responsible for what we engineers call 'load transfer delay', which is the time taken for load to transfer from one tire to other (front axle to rear or left wheel to right and vice versa). Stiffer springs causes lesser load transfer delay, Softer springs causes higher load transfer delay. Less delay means faster reaction time from tire and agility but less mechanical grip. High delay means terribly slow reaction time and driver response but a better grip on track. Now, given a choice i would surely use a stiffer spring and use the sway bar to balance the compromise on grip.
Dampers come into the picture when there is a change in momentum (sudden or gradual) of the car. If i were you, i would put the slow speed settings to max and high speed settings to min/average. Slow speed damping is what you can actually feel as a driver, say taking a turn or tackling a chicane for instance. On the other hand, it is pretty much impossible to understand the high speed damping which is nothing but hitting curbs or bumps, provided the setting is min, these do not affect the stability to an extent and helps gain better mechanical grip as seen in many off-road cases.
But these are just classic text-book methodologies and even i am looking for an expert opinion.

[DaveW]

In my view the priority list looks something like this: .......

I have a slightly different view.

To explain in a very simple way, a sudden change in load applied to a suspension fitted with springs but no dampers will cause the spring deflection to be (roughly) twice static, and the disturbance will continue because no energy is being absorbed. The addition of dampers will cause energy to be dissipated, and if the dampers are properly matched then both the magnitude and time of the disturbance will be minimized.

The maximum level of damping will depend on tyre stiffness (amongst other things). - if the dampers are too stiff then the tyres will allow the dampers to lock, and again (at least in the limit), the dampers will do no work. So a good way to think about it is the maximum spring stiffness will depend on tyre stiffness, and the dampers will be used to control both the springs and the tyres.

It is quite common for dampers to be digressive (a steeper load/velocity trajectory at low speeds) but the scope is a bit limited, see above. It is also useful to change the ratio of compression/rebound damping because that can affect static ride heights (for example). Dampers can also be used to control the lateral balance of the vehicle.

In my view dampers are, perhaps, the most important of the suspension parameters in a "mechanical" vehicle - but I would say that, wouldn't I?

[godlameroso]

I have a love/hate relationship with rebound tuning. Because it's effects are on the opposite side of the side you're adjusting. Less rebound in the rear let's the nose pitch forward under braking, and more rebound in the front reduces squat under acceleration. And stiffening rebound on the left side slows compression on the right side, and vice versa.

[DaveW]

Less rebound in the rear let's the nose pitch forward under braking, and more rebound in the front reduces squat under acceleration. And stiffening rebound on the left side slows compression on the right side, and vice versa.

Forgive me, I don't question your statements, but merely ask "Why would you do any of that?"

Only three possible reasons (for me): the damper design "prefers" a rebound biased set-up (Penske have published an interesting paper on the topic), Bump rubbers are being used to balance the car, and (perhaps) the vehicle only ever turns to the left....

[godlameroso]

You can fine tune car behavior, especially under weight transfer, let the springs packers and bump rubbers deal with most of the compression. Aren't most suspensions biased towards rebound anyway? I admit I'm not involved in much open wheel stuff so I wouldn't know but for cars with fenders almost all suspensions are biased on rebound. That I've seen anyway.

[DaveW]

Aren't most suspensions biased towards rebound anyway? I admit I'm not involved in much open wheel stuff so I wouldn't know but for cars with fenders almost all suspensions are biased on rebound. That I've seen anyway.

Dampers are multi-functional. Tradition is that set-ups are rebound-biased, and the architecture of many (Penske, JRZ, etc), makes it difficult to explore other strategies. Further, dampers are impedance sensitive, so a dynamometer test does not always reflect the way they will behave in a vehicle (putting it simply, if a damper wants to stop, it can on a vehicle, but not on a dyno).

The question is, is a rebound biased damper the best solution? Modern damper architectures (Multimatic DSSV, Ohlins TTX for example) allow the bump-rebound split to be varied without serious compromise, and these have demonstrated that a mildly compression biased set-up has significant advantages, offering better contact patch load control and lower static ride heights. Jacking shouldn't be too much of a problem if the strategy is applied to both axles.

There are several topics in this forum that amplify the above. It is worth searching for and reading them, I think.

[godlameroso]

I mostly agree. Did you know Ohlins TTX were twin tube dampers? That kind of blew my mind as surely such a high end damper would be monotube. Having the right amount of damping on all 4 types of motion is important. Not having any appreciable compression damping makes the car feel floaty and boat like.

[Nickel]

Why would a twin tube setup not have any appreciable compression damping? My understand of Ohlins' reasoning for twin tube is to be able to make adjustments to rebound or compression, low or high speed, such that only the desired parameter is adjusted. AFAIK mono tube tends to lead to secondary effects when tuning suspension parameters.

[Greg Locock]

Well the absence of compression damping on twin tubes is a new one on me. Is this some piece of racing lore?