http://www.penskeshocks.com/Adjustab...h%20Manual.pdf

http://rapidshare.de/files/19712389/...anual.pdf.html

for those who wish to do some remedial reading before discussing in depth the ultimate theory, application, engineering, sourcing, goal, innovation etc. of suspensions.

http://msspares.com/sitebuilderconte...ett44small.pdf

ohlins tt44 ^^

 

Good stuff, especially the TT44 manual

There's a setup program for the TTX44 on the Ohlins website here thats useful for seeing the effects of the adjusters.

 

IIRC those focus on the damper itself, and specifics of valving, and not so much on other points in designing a suspension system, eg. springs and spring rates. More importantly, they don't offer the reader an in depthy explanation as to *why* certain damping curves are desired, or the basics behind rebound and compression, among other things.
While those are not doubt useful in understanding the internal workings of a damper, there are better primers out there for people looking to get an introduction in the intermediate level of suspension theory (given a solid understanding of the very basics).

 

uhm... what else is there to suspension that is of any sort of complication besides the damper? a spring is a spring is a spring, you are free to discuss progressives but seriously... it doens't get too complicated especially in engineering aspects.

what other suspension components offer any sort of engineering complexity besides dampers? i'm seirously asking cuz i'd love to know.

i was trying to introduce a discussion about how certain types of valving certain types of shim stacking and certain types of auxilary resevoirs make the damping more precise or broaden the range of applicability and how things like pop off valves keep a damper from going hydraulic under very particular circumstances etc.

 

Well I'd say there's plenty of other components that make up a car's suspension, and that are involved in the handling of a car. And plenty of them get much more complicated than what is presented in articles, bulletin board conversations, and other "easy reading" sources.
If you're talking about a primer, then there is a lot to cover in terms of just springs themselves, including why certain rates are chosen, how to determine the proper bias front and rear, spring length, how the springs are cut (open end, closed end) and how this affects their performance, what the spring is made out of and how it is formed, and how the spring's actual rate will be applied considering motion ratio and the angle at which its mounted and how that needs to be factored in to design. Not to mention how to properly determine valving for a given spring rate(s).
There is also the issue of dealing with the limitations of your applications suspension geometry and layout. As as well as bushings and tires (and you know how much of a discussion you can get out of tires).
I know what you were trying to do. But damping is only one portion of suspension tuning, and by only including damping in your reading you will not see the entire scope of suspension tuning. While dampers are no doubt complicated to design, any other suspension component will require the same amount of consideration and research in order to be designed well.

 

so what were you going to contribute? as i said in the first post... it's good to read those before getting into more details.

most people know what springs look like. most people have a good basic concept of how they're mounted. a lot of intuition can bring you to the deductions you made. however hardly anyone knows how a damper really works and what functions lie inside.

if you have more detailed information for the discussion that i mention in the original post... then add... i wasn't writing this myself.

 

Um ok, no need to take it so personally man. You asked a question, I gave an answer.
Its not as simple as you make it out to be, but if you wanted to focus the discussion on dampers, then so be it, I must've misunderstood your post.

 

personally? i'm just wondering if you have anything to contribute... should i not? you seem to be in the know about suspensions, do you have writeups that you think people should read? just want to get more info for this thread.

 

Ok, amount of damping for a given spring rate... it depends, sorry. Noob brings up some good points. Start with the spring, street or track? Let's say track, rate and free length need to be chosen along with ride height that match the amount of tire grip so that you maximize the tire contact patch at all times. This means a full geometry analysis with dynamic weight transfer calculations (remember RC and CG move together in a turn, so don't just use the static RC/CG distance) and lots of testing to understand that specific tire behavior. Sway bars should be used as a tuning device here keeping the suspension as independent as possible. For street, maybe use more sway bar to keep the spring rates lower for ride quality. Assuming all that stuff is good, now damping, or think dynamic spring rate. Dampers are velocity dependent, so initial corner entry, corner apex,and corner exit, they're not doing much. It's between the initial turn in and the apex that they reach peak piston velocity and add the most resistance, or force seen at the tire. At the apex, the spring reaches max displacement. Corner entry and exit tire loads are most effected by mass inertia. If you ever look at shock linear potentiometer data, spring displacement is the x term, shock velocity is x', and inertia x". Graphed out, they're almost perfect 1st and 2nd derivatives of displacement. If you know the spring rate and sway bar rates and motion ratios, force velocity curves for the shocks, and estimate roll moment of inertia for the body, you can ball-park the tire loads. From track testing, you then determine what needs increasing and decreasing. Follow these trends even though the calculated values are not perfectly accurate.

Now how much damping? Depends on the setup, because the bottom line is grip which translates to tire loads. I won't give out the exact setup we use, but I will say what the general trend is. The more spring rate, the less *relative* damping you need. Calculate the sprung and unsprung natural frequencies of any racecar, then look at the damping ratio (actual damping / critical damping). I've done this for many cars: EVO, World Challenge, Nascar, ChampCar, etc. There is a logarithmic decaying relationship between damping ratio and natural frequency. One of these cars uses roughly the same damping force as the EVO with 7 times the spring rate!

Shocks operate in low and high speed, so you can tune cornering and bump independently, but you can't with the springs. Sway bars can help, but if it's too stiff, offset bumps will toss the car around. Compression to rebound ratios depends too, but in general controlling the rate of roll with rebound is better because that leaves the outside tire more compliant for road variations. Most setups have more rebound than compression, but aero cars change all that.

Hope this contributes something.

 

i have a question. is the less relative damping talking about how the natural oscillation frequency of a "hard" spring is such that you don't encounter as many modes of oscillation when you hit a bump becuase the oscillations are just too fast? so they don't give you those undamped type floating oscillations.

this does help a lot and it exactly what i intended the thread for.

another question, could you talk more about spring lengths and then what ratios (if there are such) to look for regarding different heights and what not. (i know i'm being vague hahaha more discussion please)

 

trinydex,

A stiffer spring just raises the natural frequency, it doesn't change the amount of higher order modes, just shifts those too. I can tell you've been reading many of the well known books and are finding some of the missing parts. The basic equation for natural frequency is sqrt(k/m). Most people use this but it is very inaccurate. If you've taken a vibrations or diff-eq course, you may have seen the multiple degree of freedom problems, which the auto certainly is. The other masses and springs have big effects on the other natfreq's. There are 7 *basic* natural frequency modes, 4 wheel hop, roll, pitch, and heave (vertical body mass). To solve the differential equation (mx"+cx'+kx=0) for this MDOF problem the m,c,k terms are matrices. It gets ugly real fast and you need to use Matlab or better yet a real simulation program to solve it, especially since c (damping coeficient) is very non-linear. So, if you look at the car as a 1DOF problem, you get some value for natfreq. If you step it up to 3DOF (include tire springs and unsprung mass), there is a ~40% difference in the sprung natfreq. 4DOF (add pitch) improves on 3 by ~12%. After this you are getting diminishing returns on accuracy with an exponential increase in complexity because the roll natfreq depends heavily on the RC movement, whereas the pitch IC doesn't move as much. These mutiple natfreq modes mean there are critical damping and therefore damping ratio targets for each mode. Since each mode is interconnected, you have to compromise because of priorities. High aero cars care about pitch more than anything else. But this is how you tune the low-mid-high speed damping in your shocks.

In general the unsprung natfreq is 8-10x higher than the sprung natfreq. This is why the body gets upset over "wavy" pavement and the wheels get out of control over wash board surfaces. Its under these conditions that the input is close to those respective natfreqs.

Spring rate is chosen based on ultimate tire grip and controlling roll, so the tire doesn't lose it's contact patch from camber/toe changes. If ride quality is important, then add sway bar to help control roll. There's the autocross trick too of putting in huge amounts of low-speed damping (dynamic spring) to control roll for soft springs, just don't take long sweepers tho. Free length is then a matter of rideheight and total travel. This is why you often see helper springs, b/c the necessary spring is shorter than the total shock travel, the helper just take up the extra gap. For motion ratios, if there is a big rising rate (aero cars again) then this needs to be factored in. They also frequently ride on multiple stage bump stops under full aero load, so that they have a relatively softer spring available for bumps at lower speeds.

Just remember this is a system, where you gain in one area you lose in another, so its a matter of finding the best overall compromise.

 

wow that was great, i guess my original question was poorly worded due to me not being in school this quarter. i guess what i had asked was: since the stiffer spring shifts the higher order oscillation modes higher in the frequency spectrum, is that what accounts for what you said? which was that the more spring you have the less relative damping you need, because the modes are higher, they're well driven by road irregualrities.

in any case you've brought some great stuff to this thread and now i believe i've made the connection that you're the joe that rebuilds the ohlins for paul? if that's the case then nice to meet you. i'm nominating you for evmguru status now haha.

 

He's the man Now you can see why I believe so strongly in our (Vishnu's) suspension methodology, it is based on real science.

It all comes down to the contact patch of the tire, keeping all four as large as possible at their optimum slip angle for as much of the corner as possible (simple eh ). That is the result of two things; the car's set-up and the drivers ability to optimize it (which ='s you go real fast ).

 

Also what he's saying in basic terms is that a stiffer spring creates more "resistance" in compression, so you need LESS compression dampening to create what you are looking for. But you will need MORE rebound to keep the spring fully damped.

 

yep, but you still need enough to dampen (maybe easier to visualize, control) the compression of that stiffer spring.

If you think of the stock 03 suspension it has a ton of damping (relatively speaking) for a "stock" car because of the soft spring rate. Stock 03's have more low-speed damping than many many aftermarket coilovers.

Since we are talking about stiffening the springs what does everyone think represents the upper limit? What is too stiff? The conventional answer is the surface and when you start to "patter" (skipping across the surface). There is another factor that for us is more relevant...why would a race car patter at a much higher spring rate than our cars???