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OFFICIAL Suspension Theory and Modification Thread

RacingManiac

Drag Race Newbie
don't all the major suspension companies out there do these calculations before they release their products? i don't care much about the ride comfort. i want to enjoy twisty mountain roads so firmer is better for me. they probably lower the car by 1" all around.

edit: posted right after you did so did not see your post

They might, but a car company usually spend 2-3 years engineering a car, with a huge staff of engineers with teams specifically focused on something like ride and handling, vs a aftermarket company who tries to put a product out 6 month or a year after the debut of a new car. The amount of work put in is not comparable. Now most of these stuff gets installed by owners who can't or won't bother to compare result, so all they need to do is convey subjectively that it feels better to drive. And much like TechEd's post on Vortex mentioned, the car lowered with stiffer spring or damper will feel more alert, more responsive, but is it ultimately more capable is up for debate....we don't run downforce, we don't need absolute flatness of the chassis or maintaining ride height. Mechanical grip comes from tires and presenting the suspension to what the tires want. That is the whole deal with keeping the ride height within the range of the stock ride height, because that's where OEs designed the suspension kinematic based on the tire characteristic. And unless you actually objectively measure gains or losses its hard to draw accurately how you have affected the car. It might feel better at 5/10th because you are working the tire harder with more load transfer due to stiffer ride, but it may well start to over work the tire at 6/10th or 7/10th and you have a very difficult car to drive. And in real world where the surfaces are not always glass smooth, bumps that might get damped out or controlled stock may well have you get into bump stop(if you are lowered) and kick you off your intended line....

This is not to say you can't get better than stock, just if you really want to you need to be prepared to do it methodically....
 

RacingManiac

Drag Race Newbie
However I do have one comment for anyone reading this, learn to drive your car and push its limits before you start playing with suspension....I don't know how many times I've heard people tell me they want coils or suspension upgrades to improve handling when all they do is drive on the street and barely push the car. Trust me the car's stock suspension is very capable, I've been tracking my car a fair amount this summer and I can tell you that my suspension has not been a limitation.

Absolutely....it also helps in my case in my first autoX with this car to have someone more experienced drive my car and was easily a couple of sec faster. If I can't get there by myself then there is no point making my car faster...
 

ElectricEye

Autocross Newbie
I really believe after experiencing this process myself that, without being scientific about it, going from stock to coils and back gives you an appreciation for the fine tuning that goes into this car's suspension engineering. I just don't think anyone less than a perfectionist with solid understanding of mechanics would be able to maintain or extract true performance gains from a lowered setup on these cars. At minimum, having corner balancing done seems like a requirement for anyone looking for more than to "get rid of that gap".

Agreed
I've always been of the mindset that the vehicles engineers worked their buts off in designing and tuning the suspensions on this and other performance cars.

I find it comical to read posts where people insist on getting rid of wheel gap, or cry "lower it" to everyone.
It borders on obsessive.

Those German engineers know what they are doing, and I'm sure they try countless variations to come up with the - yes compromise - they choose.
Yet some "tool" with a couple of dollars to spend thinks he can do better in his driveway.

I love this thread, I thank you - and will now go back to learning. :cool:
 

grambles423

Automotive Engineer
Ah, but thats not ride work. Ride engineer although speaking of rattling and sound, is mostly concerned with ride. Its hard to talk to them sometimes, as you build your shock, you hand it to them and have it installed on the car. They go out and drive around some ride loop, come back and they tell you what is wrong with it. A lot of it is just a feel thing. It can be how the sharpness in a bump is tuned out or not, or how the body settles after a whoop or a dip. The car at this point usually will be fully instrumented with string pots, accelerometers to try to find some data to correlate to the event they describe but at the end of the day their butts are the key....

OEMs keep these guys around for a long time....and I often hear when some OEs changed their ride engineer that the next batch of products don't ride the same as before because of it...

IMO unlike objective handling and balance, which coming from a racing background is easier to fathom and deduce as the data are easily correlate-able, ride work is an art in itself....

Actually, it is. Its more so the post production evaluation, but when we develop a vehicle, at our various build events we test drive the vehicle and verify build characteristics and design impementations that have been revised or have been completely changed from model to model. Literally, I hop in a vehicle, drive it into the ground and evaluate what needs to be changed, whether it be suspension components or exterior functions. I guess I should accurately say my post is an afterthought to the whole Vehicle design process.

All of this is during the prototyping phase (which is directed toward what you were talking about) and later on the pre production build phases. Normally by the latter, we have fully hashed out all design issues and are focusing more so on production related occurances and supplier part maturation. But, as you described above, the EXACT process when we develop suspension characteristics always happens before our protyping phases, normally with current production models. That is why you see test mules look like shit because they are carrying new technology with an older body style and to mimick tests that would be seen in a new platform is quite difficult. But luckily we can quantify using our various test benchmarks that we've collected from part prototyping.

Maybe it would be easier to mention that I DO work for an OEM as a Vehicle design quality engineer and we DO part testing exactly as you named above. Actually I know a buddy of mine that was responsible for a design change for Ford's revoknuckle system that saved them a lot of money and actually quelled torque steer by a factor of 5%. Not bad......
 

grambles423

Automotive Engineer
Agreed
I've always been of the mindset that the vehicles engineers worked their buts off in designing and tuning the suspensions on this and other performance cars.

We do, as a team. I know guys in our chassis group that absolutely despises modification to the suspension just because they work so hard to fine tune it to have some Joe Schmo destroy it.

I find it comical to read posts where people insist on getting rid of wheel gap, or cry "lower it" to everyone.
It borders on obsessive.

I agree, which is why I'm trying SO HARD to figure out how to make my car perform with better aftermarket parts...or just go back to stock. I wonder if people actually realized how much thought went into making the suspension perform the way it does........Whenever vehicles are designed, there is sort of what they call a "THEME" to every project. One of the GTI's theme was defintely suspension compliancy. Thats why it does so well stock. Then people have to wreck it and slam it to the ground and expect the ride to be not affected.

I bought the car with Neuspeed Sport Springs and Bilsteins Sport Shocks and I immediately could tell there is absolutely no communication between spring and shock. I really would love to go back to stock, but I feel I would miss my ride height (Which i could get over eventually). I think FSDs might be the perfect balance.
 

Bender1

Banned
This thread




Seriously though this is about as informative as they get.

What springs are you thinking of running with the FSDs?
 

ElectricEye

Autocross Newbie
Thanks for your response grambles423 - I'm truly a laymen, and will readilly admit it.
That's why it's so great to hear from someone who obviously knows what he is talking about.
Yes, I've always imagined suspension engineers cringing at what some people do to their hard work.
I don't golf, but I find it similar to someone going out and buying an expensive set of clubs, taking them home and filing down the heads.:yikes:
Then saying "Bro' looks great!"
Great? You just ruined them!
 

grambles423

Automotive Engineer
What springs are you thinking of running with the FSDs?

I'm got the Neuspeed Sports. I'll probably just stick with those. It it all gets too annoying, I'll just slap the stockers back on.


Thanks for your response grambles423 - I'm truly a laymen, and will readilly admit it.
That's why it's so great to hear from someone who obviously knows what he is talking about.
Yes, I've always imagined suspension engineers cringing at what some people do to their hard work.
I don't golf, but I find it similar to someone going out and buying an expensive set of clubs, taking them home and filing down the heads.:yikes:
Then saying "Bro' looks great!"
Great? You just ruined them!

I appreciate it. :thumbsup: I try to stay confidential, but diving into specifics of what OEMs do really make me wanna break that confidentiality and tell all secrets. If ever anyone...ANYONE offers you all a position in the automotive field (More so with an OEM) take it. My love for cars took me down a road early in my life, and I NEVER thought I would be so deep in the company today.

Its hard though, owning a vehicle your company doesnt make. Its not really shunned, but more so people ask, why the hell didnt you buy a *****??? Because, my love for the GTI started back when I drove a MK2 GTI when I was only 11-12, then was exemplified when I drove my buddy's MKV a few years back. I'm know as the "traitor" lol but I destroy almost every car in the parking lot with just a stage 1.
 

D Darko

Ready to race!
THIS is the kind of thread I joined the forum for...Thanks for posting this type of info gentlemen. Keep 'em coming....
 

grambles423

Automotive Engineer
Can one assume that a high-quality coilover has properly paired springs and dampers (an H&R for example)?

I know they might not be properly paired to our suspension, per-say, but at least engineered together?

Yes. That is the whole point. They are designed TOGETHER to effectively help aid in ride quality and performance.
 

grambles423

Automotive Engineer
Continued

Enough chit chat....Lets continue. Again, I will keep this vague with as little mathematical derivation as possible. But, should you want to dive further I would definitely brush up on differential equations and basic physics.

I have found my interest lies within the damping aspect to determine my ride quality.

Relationship between spring and wheel rates

In general the relationship between spring deflections and wheel displacements in suspensions is non linear, which means that a desired wheel-rate (related to natural frequency) has to be interpreted into a spring-rate.

Suspension or motion ratio = Spring force/ Wheel force ******(Not the same as spring rates or wheel rates)

To find ANY motion ratio, jack the car up and let the suspension hang. Measure the spring length at this very moment. Then use the jack and deflect the wheel a given amount of inches. Once you do so record that and then measure spring length again. Use those numbers and relate it to this newly derived formula:

Motion ratio (R) = [Final spring length - Intial spring length] / Wheel deflection

Normally, you will know your spring rates. its as easy as searching on google. If you know your spring rates, then you can relate them to a spring energy formula....for the sake of no confusion I've derived it into its simplest form:

Wheel rate = Spring rate / [Motion ratio^2]

Motion ratio results from the same kinematic suspension analysis that gives camber gain and roll center. Note that R is usually greater than 1, so the wheel rate is less than the spring rate. R is not constant; it varies as a function of v. But on an front handling car, it will be close to the ride height value at both full bump and full droop. Once the desired kw is known, and R has been determined from a candidate suspension geometry, ks may be determined. Note that the spring’s own free length (i.e., under no load) corresponds to full droop and not to ride height.

Dampening and Natural Frequency

From Happian Smith:
Frequently called shock absorbers, dampers are the main energy dissipators in a vehicle suspension. They are required to dampen vibration after a wheel strikes a pothole and to provide a good compormise between low spring mass acceleration and adequate control of the unsprung mass to provide good road handling.

Might Wanna Look at Wiki too.....Click Me

Twin tube vs. Monotube


Good Read: Twin Tube vs. Monotube....CLICK ME

Basically Twin tube = comfort; Monotube = Performance

Back to the good stuff. While skipping the boring and tedious derivations, the undamped natural frequency is:

Nat. Frequency (omega) = Square root(wheel rate / sprung mass)

If the wheel rate is maintain constant, the natural freq decreases as the payload increases. It is possible to determine a variable wheel-rate which will ensure that the natural frequency ramains constant as the sprung mass increases. (More on that later)

Effective corner damping coefficients may be set by the damping ratio:

damping ratio (ζ) = effective wheel damping ratio / (2*omega*mass of the vehicle)

- Critical damping (ζ=1) is the boundary limiting oscillation after disturbance.
- Slightly overdamped (ζ=1.2) will keep the wheels hard-pressed to the ground.
- Slightly underdamped (ζ=0.6) will allow more rapid response to disturbance say rolling into a turn) without much oscillation.
- More underdamped (ζ=0.35) will allow rapid wheel deflection, such as necessary to follow a rough surface.

This part is hard because companies do not give these values. But you can calculate a critical damping ratio and go from there. You can see that there is A LOT of fine tuning that goes into this.

Look at this pic:

Normally you want to find that range of overshoot to not allow the car to go haywire when you hit a bump, but also you dont want to car to overshoot and bounce like a pogo stick when hitting a bump and returning on the rebound. Again, you can solve for which damping ratio you'd like and find a coefficient of damping and go from there. You might be able to ask companies for their values, but be warned, they might not give it to you.

Happian-Smith:
In dealing with road surface undulations in the bump direction (damper being compressed) relatively low levels of damping are required when compared with the rebound motion(damper being extended). This is because the damping force produced in bump tends to aid the acceleration of the spring mass, while in rebound an increased level of damping is required to dissipate the energy stored in the suspension spring.

What is the ultimate design? A controllable suspension (DCC) that electronically controls the adjustment forms of the basis of improving ride and handling. AKA Sport Standard and Comfort. Most companies design for the middle, but what the user wants to decide between tracking and daily driving? This system provails.

The biggest is when you chose a static spring and shock setup that has to balance the two: Comfort and Sport. Thats where multivariable input shocks such as Koni FSDs come into play. Basically just a valve that has high limits that soak up the major bumps in the road, but at slow compressions, such as during turns, they act as a performance shock. Still....when does the valve open? Thats left for some interpretation and subjective reasoning to deteremine "ride quality"

An objective approach to ride quality will be discussed further, when I can collaborate my notes a little better....Stay tuned.......
 
I've had multiple suspension setups over the years. from coilovers to cup kits to seperate spring and shocks. The coilovers rode very nice, but I didn't have them slammed like some people do. They were in the middle to higher end of the adjustment. I just wanted to get rid of the gap without being too low either. had alot of travel and it was a good handling and ride quality. The only thing is that once I found the perfect height for me, I never touched them again.

On the mk6, I think the best setup would be DG springs with either sachs GTI shocks or Koni yellow sport shocks.then add some swaybars if you want to push it more. If you can't find the GTI shocks at a good price you could always use the new koni strt shocks too.

I think with the DG and koni sport you would have a pretty good setup for handling and ride. you can fine tune the ride with the rebound adjustment. The springs lowers just enough to give you a nice look without looking too low. Anyways too low is bad for handling. I also want to retain some ground clearance because the winters are harsh here. another good thing with the konis is that as you rack up the miles, you can turn up the stiffness to compensate for wear of the shocks. When a shock wears down, you always lose some dampening.
 
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