SundayDriver

I set my double adjustable shocks as hard as I can for compression and as soft as I can for rebound. If you are too stiff on compression, the car will be harsh, tiring and will behave badly over bumps. I can run much stiffer at Mid Ohio than at Heartland (bumpy track). Still compression keeps the tire in contact with the pavement as you hit a bump.

On the drop off side of the bump, you need it as soft as possible to come back into contact. Soft rebound also allows much earlier application of throttle.

Some of the best things to do are:
Set shocks full soft (B/R) and drive the car.
Repeat for full stiff.
Back off full stiff compression until the car is comfortable and controlled over bumps.
Do the same with rebound.
Go to full soft and move one at a time to develop feel.
Keep doing things like this to get a feel and teach yourself that some stuff is not all that intuitive. If the car is hopping over a series of bumps, the rebound is probably too stiff, rather than the compression being too stiff. If you feel like you are waiting for the car to settle in esses, again, rebound is probably too stiff.

Learn to trust what you feel. Have someone make setup changes to your car without telling what they have changed. Do some laps and tell them what is different. Maybe they did not really make a change that time.

Get a copy of Carol Smiths 'Engineer in your pocket'. It is the best practicl tuning guide you will find.

PatK-Mpls

Do you tend to adjust the front and rear together or make those determinations based on turn entry/exit needs from the car?

SundayDriver

If a track us much bumpier or smoother than another, I will make a moderate change to both ends. The way my shcoks are valved, alignment and spring rates, it is neutral to slightly tail happy with the front and rear shocks set the same. Hence I almost always start with identical settings front and rear.

From there, I tune one end or the other as needed. My car is very stiff (wheel rate is about DOUBLE the corner weight) so it responds highly to shock changes.

seege

Is Heartland still bumpy after the repaving they did?

ColorChange

The proper way to analyze shock setup (assuming you have a DAS) is a frequency and/or displacement analysis. I am not willing to go into that here as that analysis is well beyond a simple g-sum concept and too many people here seem to be having trouble with that. Furthermore, until you can consistently drive your car near the limit all the way around the track, detailed work on the car/setup is largely an unnecessary distraction.

SundayDriver

It should be very smooth now but it has not been run yet. Not sure they are finished with the re-pave as it is running behind schedule.

SundayDriver

That is why you are so entertaining and insulting...

First, you tell us we are all too stupid to understand your expertise. (BTW - Have YOU ever tuned the shocks on a car using DAS or is this another theory?)

Then you saywe are wasting our time if we can't drive at the limit. Since this is my thread, and Pat is the other primary participant, I take that as a statement that neither Pat nor myself are capable of driving at the limit like you are. Or is that just more theory too?

Of course, if you were really smart and really understood this stuff, you could explain it in a way that even us inbred idiots could understand.

Robert Henriksen

I'm gonna go out on a limb on this one, but let me guess: he's not stating this as theory, he's stating it as fact.

Hope that helps!

Mark in Baltimore

When I think it can't get any worse, I read something like this. Astonishing....

Mark, thanks for the knowledge given to those of us who can admit that we have much to learn.

924RACR

Distractions in the thread aside, this part interests me greatly! Is that consideration of very stiff - is your reference relevant only for sports racers and formulae cars, or would that by any chance carry over to our door-slammers?

Larry Herman

Mark, I have found that too much rebound will tend to mimic bumpsteer in undulating corners. The steering is loading and then unloading because the wheel cannot return to the road fast enough. I would keep softening the rebound until the car can smoothly track over the undulations. Any thoughts on this?

Adam Richman

I think you may get there but not by the right way. I'd try softening bump to smooth it out over undulations (but I am thinking you mean road imperfections, not the dip at Road Atlanta). In general, you will want to handle the smoothness/trackability of the car over bumps or small undulations by adjusting bump, not rebound. What I have found w/ far too soft rebound is that the car will oscillate off of compressions (not just bumps but coming off and even through longer turns) and w/ far too firm, it will jack itself down on the loaded (last loaded) side (as it is resisting coming back to center). To _me_ its far easier to adjust rebound from full soft to stiffer as I want to adjust up until the oscillation goes away (I think its harder _for me_ to feel it rolling less). Your comment about mimicing bump steer is not something I have felt but it makes sense, too stiff rebound damping up front will allow the car to continue to jack down under braking.

Bob Rouleau

For CC's benefit, having a better suspension set up on a Ferrari Challenge car took more than 2 seconds off a "best" lap time. Changes on the F car are limited by the rules, so it' spring packers and changes to the ride height (no aero tricks like Mark has). And yes, the driver is absolutely great.

Mark if I may, you set compression very hard and rebound soft to maintain contact. How is the ratio of compression to spring rate? I think you hinted at it, but I'm not sure I understand it. Rebound has to be firm enough to prevent oscillation. Are you using realtively soft springs and using the shocks to manage compression? Note the GT3 set up seems to do something similar. The shocks are way stiff and the spring rates are low. Rebound on the bilsteins is fairly stiff and I think there is room for improvement there .. or, my shocks are shot , which is possible after 12,000 odd track miles.

RedlineMan

Mark; Save it, Bro. We already know how ignorant you are. Thanks!

Larry; If I may. You are probably feeling the impact-float-bam-float-bam of too much rebound keeping the wheels from returning into the valleys of bumps. I had not considered it, not having discrete adjust myself, but you are likely correct in your theory of steering subterfuge.

And so from this we learn that...

If your car handles like a bag a crap, or even if it is only off by a tad, and you are not Michael Schumacker, just shut up and drive. You have no business trying to make it better, and will probably make it worse. Do not attempt to lay down a baseline and then build a knowledge base - as dear Sunday has suggested - for understanding by probing the cause/effect workings of your suspension adjustments because you are not yet worthy of such success and enlightenment.

Or, could the reason for your not "reaching the limit" be that you CAN'T because you must remain ignorant and not touch anything? Or, are you reaching a "false limit" because your car is a pig?

Stunning. Simply stunning.

hrk

Yes,

The natural frequency of each corner depends on sprung mass, unsprung mass, and wheel ratio.

Formula I've used would be
=187.8*SQRT(wheel ratio/sprung weight)

Wheel ratio can be determined by spring rate and ratio how it affects wheel (leverage and angle)

Sprung weight is a bit more difficult. I had corner weight, then I weighed the wheel and the sprung mass of suspension arms, brakes and such by removing spring and putting it into ride height.

"
Ranges of frequencies commonly found in different types of vehicles are:
Very soft passenger car: 0.5 to 0.8 Hz (30 to 50 opm)
More sporting passenger car: 1.0 to 1.3 Hz (60 to 80 opm)
Modern sports car: 1.1 to 1.5 Hz (70 to 90 opm)
Pavement race car with modest downforce: 1.5 to 2.0 Hz (90 to 120 opm)
Modern race car with ample downforce and ground effect: 5.0 Hz (300 opm) or more
"

hrk