utkinpol

Not to stir the local pot again ,
i just want to figure out something for myself as some older threads i started on other forums gave a bit of conflicting info. And I just love to do my RTFM before i get to try it live.
So pls don`t get overly upset over all this as I will try just to summarize this information as i was able to collect it, it got nothing to do with my current (lack of) skills , it is purely a theoretical exercise. I just like to rationalize and put labels with numbers on all that empirical stuff real drivers feel with their guts.

statement 1:
proper order to prepare suspension for an event is to choose correct rate for springs based on track conditions, then set shocks to average medium soft settings all around, then adjust sway bars and after point when sway bars are set to desirable understeer/oversteer level - one gpt to fine tune shocks compression and rebound in combination with tire pressures.

in this statement typical controversy seems to be in the area what gets tuned first - shocks or anti-roll bars? I really hope it is not an another egg-chicken class of a dilemma, and if it is - just say so pls so i could get it out of my mind.
or perhaps it is totally inadequate as a concept? so please comment.

statement 2.
adjust front sway bar for turn-in understeer, adjust rear bar for turn-out oversteer.
OR like this:
Corner entry push, soften front bar.
Corner exit push, stiffen rear bar.
Corner entry loose, stiffen front bar
Corner entry loose, soften rear bar.

Does it make sense?

statement 3:

it is obvious that understeer/oversteer behavior is controlled by a stiffness ratio between front and rear bars, but what absolute stiffness should be chosen in what circumstances assuming we preserve same final ratio?
best explanation i was able to find so far was on this forum and it was like:

bumpy track....bigger sway bar (overall), smaller spring (overall)
smooth track....smaller sway bar (overall), bigger spring (overall)

So is it possible to give more numerical definitions to 'bumpy'?

I would really prefer to keep this purely theoretical and do not get to details of my particular car and of my particular setup as all I want to gain from this is to get some sort of a better understanding of this voodoo process as a whole. I never saw a thread where this topic would be covered in level of details that does not let anything left out, all I saw was always partial - either shocks, or springs, or bars, or tires. but never all of it together and thinking logically it does work all together, so it has to be setup taking all those parts into consideration, is that a correct assumption?

PS. I do promise to keep number of my responses to lowest possible minimum.

Land Jet

You tee-ed that up real nice for the boys, now let's see what they can do with it.

First I have to ask, are you looking to learn something or are you waiting for answers so you can tell them how full of sh*t they are?

beentherebaby

I just drive Flat Out and don't worry about the suspension. That's me Flat Out.

mrbill_fl

honeslty, I'm a noob on suspension tuning.. but would say put them in the middle of the range.

At this point, it really doesn't matter. its about how the car feels, and adjusting your driving to meet what your car is doing.

-I have run cars with rain tires in the dry and they felt very greasy, but could still keep up, by taking it easy, braking hard and using what the car could give me....

its all about what the car can give you and using it. -if you are concerned let a hot shoe take the car out for 3 laps with you in the rt seat... if you can come close to their times, you can start to worry about setup. - pcars are very good right out of the box!


we are talking about track events, not Autox, correct?

utkinpol

i cross my liver and do promise to wait for at least 5 more answers to appear in this thread prior to responding anything to anybody nevermind of what I will think.

utkinpol

I just promised not to respond but it is a valid question.

honestly i do not think any type of event would have direct relevance here as it is more of a generic setup question.
obviously depending of anticipated speed and driving style there are more components there as camber, caster, stiffness of tires sidewalls, etc., but i did not really want to go _that_ deep as we will get lost there completely and tried to sort of limit this exercise with springs, roll bars and shocks as primary model components.

i just was thinking that despite of what it is - street driving, auto-x or track or rally or drifting show - driver does know up front more or less how he wants car to behave - does he want to let *** turn around or to be glued to the surface, etc, like there is a some sort of empirical expectation of how car _must_ behave and then we take wrench into our hands - so, what do we do next after that exactly, considering car was 'reset' to defaults and shocks are taken off, there are no springs on, zilch - totally blank page? BUT i tried to limit that to 3-4 major tasks and I tried to put them together in the first posting as no one will be able to cover whole topic in one response probably.

i really do not want to over complicate all this as it is VERY complicated indeed.

what i ask is how pro people deal with this problem and what steps are getting taken usually to find an 'optimal' setup, 'optimal' grip.
i was just sort of thinking that overall list of tasks to be done, a 'project plan', to say so, has to be pretty much the same, right?

TRAKCAR

mrbill_fl

you could always buy the 'bible' fred puhn's how to make your car handle...
I have it, and some of caroll shelbys books... plus the speed secrets series books.... and I'm still lost.

http://www.amazon.com/How-Make-Your-.../dp/0912656468


-going for 8 pages... jump in!

SundayDriver

This can get very complex, but I will stay at a high level. First understand that some of the complexity is that setup is an iterative process. Do A then B then C then back to A, etc, etc. But you never get finish because conditions are changing as you chase the setup. Also, we are dealing with different drivers. The fastest setup may not work for a given driver because they are not comfortable in the car. That said, here is the basic answer...

Springs are first. You are going to start with what someone else tells you is right for the car. Softer is better mechanical grip. Move softer and softer and the driver starts to feel uncomfortable. Very stiff springs are used to maintain ride height for aero cars. Spring rates control the platform, roll and pitch. Balance the spring rates to get the handling you desire (over/understeer). You can't do that in a vacuum as the shocks will be in play. If you are really tuning springs, I would do that with the ARBs disconnected.

Second step is ARBs. Finer tuning than springs and much easier to change so that is your coarse tuning tool at the track. Do not chase entry or exit conditions with ARBs until you are done with shocks. Focus on overall balance and mid-corner balance to tune the bars. In the vein that softer is better mechanical grip, you will probably get best results by softening the end that will change the balance in the direction you want.

Finally, shocks. Remember that shocks only affect the car in transition. Once the suspension is set for a corner, the shocks don't control the handling. Start with full soft bump and rebound. Stiffen the bump until the car does not feel comfortable. Then stiffen rebound until you are waiting for the car to settle in transitions. Esses are the easiest section of track for that aspect. Once you stiffen rebound until you feel that the car is not coming back quickly enough, back off slightly till you get the car settled quicker.

Cycle back to springs/ARBs/Shocks as needed.

That is the simple model.

utkinpol

can you pls jump just one level deeper and explain, hmm, not sure how to ask, essentially if a person buys a stock gt3 car and then decides to replace stock ARBs with GMG bars which are 1.5 stiffer or so - how does it play into the rest of the game? TPC bars as I understand it are even more stiff, so, do they really need that only for stock cars with relatively soft springs or would same stiff ARBs be used on a cup car which has very stiff 1200+lbs springs?
How do advanced tuners decide what generic base stiffness if required for ARBs in what particular situation?

continuing with springs i sort of understand that with basic springs rates one got to rely on previously collected knowledge of what 'works' best on what track as there is no universal setup.

But, is there any, not sure, a formula perhaps for appx springs rate computation that would take to consideration car corner weight and roughness of the surface? I am just curious how do people come out with exact springs rates like TPC suggests using 900lbs all around, my mechanic always supplies GT3 cars with 600/700lbs or 700/800 preserving 100lbs split, some folks insist on bigger split like 600/800, I even saw samples like 750/900lbs and I am not talking about shocks valving here, only about generic assumptions one uses to choose appx spring rate.

Does it make sense in the way how I composed this sentence? as I am not sure myself what is it I am trying to say here. essentially - may be better way to say this would be - where the heck this decision about 600/700lbs springs even came from? is there a certain rule what percentage of corner weight should correspond to what spring rate? or else?

SundayDriver

I'll try to respond...

There are some 'rules of thumb' but they really apply at the design or early development stage. I don't really know what those are for a street based car. But, as an example - sports racers usually start with a wheel rate of ~2.5 times the corner weight. For reference, that would mean a rear spring rate for a 911 in the range of 3500-4500 lbs/in. At those wheel rates, you need very little ARB and it exists only to trim the car, it the car even has ARBs (some do not).

In a street-based car, you will run much softer and the ARB will do far more of the work. But converting/improving a GT3 is starting well downstream of the early development phase. There is no 'rule-of-thumb' that I am aware of, that will help. You must rely on experience - that can be your own experience or that of others. The best path is to use the experience of other people to get you close. If you have enough personal experience, then you can fine tune the characteristics that work best for you.

One of the big reasons that general rules don't work very well is all the compromises you start to get into, that can vary from car to car. For example, if you lower Car A the suspension geometry is all messed up - bump steer and camber gain are really bad. But Car B (different model) has OK geometry when lowered a like amount. You might have an idea that both cars should use the same spring rate, but that rate allows too much travel in Car A and the suspension geometry kills the handling of the car. A stiffer spring rate, even if it costs mechanical grip, might make the car much faster as the suspension geometry is being kept in a better range due to the stiffer springs.

Bottom line is that there is no magic bullet for those of us trying to tune a car. Each vendor has their own setup - partly because they have experience that says it works, partly because they used different drivers/conditions to do the testing and partly because the buyers 'think' something should be true (like a bigger ARB is better). I know this isn't the answer you would like - I too looked for this magic formulas and they really don't exist.

M758

Listen to Mark.


Suspension tuning is part art and part science. Mark has explained the science of it. In fact it is rather simple in that light. The art comes in dealing with neuances of each chassis and dealing with particulars of each track.

utkinpol

Yep, it makes perfect sense. I do not even attempt to rebuild anything in my car - i trust my mechanic who does it for 20 years now so he knows pretty much what is correct amount for my type of a car to be lowered to, how geometry of arms should be preserved and a lot of other stuff i do not even try to comprehend. Just too much info.

I was generally curious about mathematical part of this design process, if it was any and as I see it now a bit better it is really, well, complicated.
Thanks a lot for your great response, it was really helpful, I appreciate it.
Thanks, Paul.

utkinpol

Well, it is quite true, but as you said yourself - there are plenty of nuances.
What I have now in my car suits me more than enough and is head ans shoulders above of what I can actually use. Still, I like to have this adjustability and do not regret paying for it, even if for most part of this and next season it will not be even touched.
But I always believed in everything I do that one got to know perfectly well how any system works prior to trying to use it and with this suspension stuff I am still not sure if I do understand all those little details. well, it is not critical of course, as it still works whether I do believe into it or not

Choosing 'optimal' springs rates is still a mystery to me - how do those tuners decide what works and what does not, why p-cars originally use progressive springs instead of linear if all tuners install linear springs only, etc, etc. But I guess it would be better just to stop worrying about all that if it really does not have any definitive answer anyway.

2BWise

This is the real bible: The Bible

This is such a complex subject. There is quite a bit of reading material out there that will be so much more useful than pages of posts here. It all depends on how in depth you'd really like to go. Do you just want to be able to tune the vehicle to you're liking, try the Carrol Smith books. Do you want to mathematics and the derivations, try RCVD, above. There is some of the good articles here as well: OptimumG

Mark has explained some of the basics well but even he could probably fill a few pages if he were to really jump into it.