CSG and RCE tag-team suspension Q&A thread! Ask us anything!

[Dimman]

Originally Posted by cdrazic93

From the difference in design is there any way in which the double wishbone is better?

Double wishbone provides the potential for superior geometry control, particularly camber. Also MacStruts have more sliding friction.

But as in most things, the application is more important than the base tech.

The Hyundai GenCoupe has a more complex front strut design with virtual steer centers (à la BMW) through two lower links, and more links in the rear multi link suspension. But they didn't execute it anywhere close to the 86.

[7thgear]

sometimes lo-teks get the job done

one thing to remember is the original AE86... macstruts out front with the ghetto 5-link, solid rear axle in the rear.

but dat shit worked mang.

[cdrazic93]

hmm...seems simple is the new complex

If I had my own shop, I would be that guy to try and make a pushrod suspension fit into this car lol

[Dimman]

Originally Posted by Calum

My comments are in bold.

Adding to point 3, this is one of the reasons we shouldn't (even though I know I do all the time...) compare true race to production tuning too aggressively.

If the suggestion was made in designing an LMP or Formula car that they should stiffen the springs to control the geometry, that engineer would probably be terminated on the spot. They control the geometry by designing the appropriate geometry.

Conversely if one of us was having problems with camber control and RCE recommended we redesign and fabricate the entire suspension geometry, we'd all look at them like they were crazy.

Different fields, different constraints.

[cdrazic93]

Originally Posted by Calum

My comments are in bold.

Within the limits of quickness and slowness, the very quick transition of weight onto a tire rather than progressively loading it, like RCE said; I think it would be like stepping on a bar of soap, it's going to shoot from your foot. If you step on it progressively with your weight, it's going to be less likely to shoot from your foot.

[Calum]

Originally Posted by cdrazic93

Nope not yet! This is all inundating my brain and like slamming a dictionary on my head hoping to learn lol jk

I've dealt with frequency before, only in audio though.
I know nothing about impulse response, dampers and settling time.

Have you ever built a subwoofer box? The suspension (notice the similar term) of the driver dampens the cones movement. The properly tuned port can also dampen the movement of the woofer at certain frequencies and allow it to move more freely at others.

In designing a band pass filter (crossover) for the midrange you are using capacitors and inductors to create a natural frequency that will get passed to the woofer. There's roll off rates that are effected by order of the filter, 20dB/decade (or 8dB/octave in audio terms) is the gain of a first order filter. This is the typical butterworth filter most prefer as it has very little ripple and low phase change. That filter is nothing but a control system, reacting to inputs. Some inputs are allowed to pass through, others are damped or attenuated.

An impulse response is something that's only theoretical when it comes to analog control systems. Don't worry about that for one for now.

The biggest thing here is understanding how the different elements of the control system affect each other, and that we can't practically isolate things like pitch, roll, rebound, and compression.

I'm doing my best to understand and see in my mind how everything works together, but every time we head down this path I want to go back to my old job of using 70 year old pneumatic control systems to maintain a ships speed at sea; everything from ensuring the prop doesn't overspeed if it comes out of the water to maintaining the water level in the boilers. I never imagined a cars suspension would be so complicated as to make that seem easy.

[Racecomp Engineering]

Originally Posted by hakkoo

Quick question, I have the ST Coilovers, do i need to get camber bolts to adjust front camber or is it okay w/o it since ST's are slotted

Thanks

Slotted front means no need.

- Andy

[7thgear]

Originally Posted by cdrazic93

; I think it would be like stepping on a bar of soap, it's going to shoot from your foot. If you step on it progressively with your weight, it's going to be less likely to shoot from your foot.

sorta

but also with the point being that you want to step on it as quickly as possible

you can design a car that will take a long bend (like a highway ramp) at very high speed, but if you tell the same car to do a high speed, short spaced slalom, it wil fail horribly if not tip over alltogether.

so the question is, what are you tuning for, given that most production cars are by design limited in their design.

[Racecomp Engineering]

Originally Posted by cdrazic93

Rather than going for the cheaper option, miata or the like, I would attempt this only due the fact of how different the car would sit and feel on the road and track, the unique appeal also has some allure to it as well

I think some team converted an evo front end from strut to double wishbone on a time attack car. Not 100% sure if that's true. It might just be...wishful thinking.

Might be impossible to do on a car with a boxer motor due to packaging

- Andy

[Racecomp Engineering]

Originally Posted by Dimman

Adding to point 3, this is one of the reasons we shouldn't (even though I know I do all the time...) compare true race to production tuning too aggressively.

If the suggestion was made in designing an LMP or Formula car that they should stiffen the springs to control the geometry, that engineer would probably be terminated on the spot. They control the geometry by designing the appropriate geometry.

Conversely if one of us was having problems with camber control and RCE recommended we redesign and fabricate the entire suspension geometry, we'd all look at them like they were crazy.

Different fields, different constraints.

Very much this!

We can learn some lessons for sure but we also have different constraints.

- Andy

[Racecomp Engineering]

Originally Posted by Calum

Wait, side to side weight transfer isn't affected by roll angle? I thought stiffer springs would help manage roll which will help manage weight transferring to the outside tires.

Total weight transfer for a given corner at a given speed is down to COG, track width, and total weight of the car.

What we're doing with springs/rollbars/dampers is trying to control the rate at which it occurs, the distribution of that weight transfer, and minimize the changes in suspension geometry due to body roll.

With regards to distribution of weight transfer and I think where you might be getting mixed up...we can stiffen the rear which means more weight transfer at the rear. Since total must remain the same, this means there must be less weight transfer at the front. Less weight transfer at the front means more evenly loaded front tires. More evenly loaded front tires means more grip up front. That's why stiffer rear = less understeer. There may be additional affects from a stiffer rear like keeping the rear from rolling too much, reducing positive camber gain, and thereby keeping the tire nice and square on the road for a little more rear grip too, but it depends.

- Andy

[7thgear]

there's also this thing where a flat and stiff car gives people confidence attacking a corner because the car settles quicker given the entry speed... and also most people don't like to be axially rotated... this fucks with their brains and forces them to shift their bodies/heads to maintain forward vision

not a fun thing to do at over 100 kph or in a prolonged slalom

[Racecomp Engineering]

That too. Too much chassis movement doesn't give confidence in a car.

- Andy

[wparsons]

Originally Posted by Calum

My comments are in bold.

I'm not positive, but I believe the science would say that stiffer springs don't control weight transfer in a corner, they just control how much compression travel you use from the weight transfer.

That said, I do think that excessive body roll will end up limiting weight transfer because the tires don't have a good contact patch so you can't generate as much cornering force, and less force means less weight transferring.