Suspension: When to adjust what?
 

Everyone knows the flow chart that tells you to adjust the front/rear of the side that slips or grips, I want to take it a step further so here are a few questions I've had over the years that I'd like to get clarification on:

If I have 50/50 cross weights, how do I adjust for the F/R weight ratio for neutral handling?
How do I know when I need to adjust spring rate?
How do I know when I need to adjust sway bar stiffness?
How do I know when I need to adjust the rebound knob?
If I feel the front of the car rolling, and the rear flat, is that necessarily a bad thing?
Why does my car feel planted going over curbs or big 1" dropped grates in the road, yet slightly "pogo" over undulations in the road? I'm thinking this new valve may be in order (blue line, from AST's Facebook):
http://a2.sphotos.ak.fbcdn.net/hphot..._4138903_n.jpg

lot's of views, no answers, not surprised.

What are your spring rates? and what sway bars do you have right now?

:hustler:



You'd probably get a better more in depth and accurate answer from first reading past issues of Mark Ortiz's Chassis Newsletter, then posting a specific question directly to him.


http://www.eviltwinmotorsports.com/?page_id=204



In response to your last question.


The Mark Ortiz Automotive
CHASSIS NEWSLETTER
PRESENTED FREE OF CHARGE
AS A SERVICE TO THE
MOTORSPORTS COMMUNITY
August 2000

WELCOME
This newsletter is a free service intended to benefit racers and enthusiasts by offering answers to
chassis questions. Selected questions will be presented, at my discretion. Readers are invited to
submit questions by mail to: 155 Wankel Dr., Kannapolis, NC 28083; by phone at 704-933-8876;
by e-mail to: markortiz@vnet.net
Mark Ortiz
“THE SHOCK DYNO LIES!”
How come if I dyno a Bilstein shock (Roehrig dyno, using their software), and then duplicate the
graph exactly on an Ohlins, the shock feels completely different to the driver? I mean different as in
no side bite, and no forward bite – but the driver says the car doesn’t feel any stiffer.
Also, if I vary the gas pressure, the dyno displays the same graph, but the driver can feel a difference
in the shock. Why?
At what point in rebound/compression valving split will jacking occur? We valved an Ohlins to be
exactly like our Bilsteins, and the Ohlins ratcheted down in the turn until it bottomed out and almost
scared the driver to death.
How do I match the shocks to the track surface for maximum compliance and therefore maximum
forward bite? The tires of the winning car in the 100 lap day show seemed to just roll over the
washboard surface, and on all the other cars you could see the tires bouncing up and down.
The tracks get rough, and because the roughness is caused by the same type of vehicle, the roughness
always has the same look. I would think that since the pattern of 3” to 4” holes and bumps is always
similar, the “perfect” spring frequency and shock valving could be found. How do I test for this?
The shock dyno doesn’t lie, but it doesn’t tell the whole truth.
First of all, I believe your dyno cycles the shock through a 2” stroke, normally near mid-travel,
at 100 cycles/min (1.67 Hz). This gives a peak velocity at mid-stroke of just over 10 in/sec. A
rough dirt track may give you shaft speeds above that.
Your dyno only generates simple harmonic motion. Other companies make more expensive
dynos that can generate approximately square-wave (very high acceleration) motion, or can
reproduce on-track motions recorded by electronic data acquisition. These modes of testing
have value because shocks are sensitive to acceleration as well as velocity.
Your software can be programmed to show you various outputs. Many people look only at one end of the stroke, most often the extended end (rebound valving closing, compression valving
opening). It helps to look at both ends. A plot showing both ends of the stroke, force versus
absolute velocity, will have two points or noses at the left side, and four traces. I have seen
instances where looking at the full stroke showed me acceleration sensitivities that I never
would have known about if I had only looked at the extended end of the stroke.
The usual thing the program does with the gas force is to re-zero the load readout after
stopping momentarily at mid-stroke and reading the gas force. However, the program should
tell you, as a numerical readout, what that gas force is. It will vary with the pressure you put in
at build, and also with the volume of the gas, which you control by varying the floating
piston’s position at build or the oil volume you pour in.
You don’t always get the same trace with different gas pressures, even with re-zeroing. More
gas pressure actually increases rebound damping force (with gas force omitted), due to reduced
nucleate boiling (incipient cavitation) on the downstream side of the piston. This effect is
greatest at high velocity, with a stiff rebound stack, low gas pressures, and hot oil. The effect is
least – sometimes unnoticeable – at low velocity, with a soft rebound stack, high gas pressures,
and cooler oil.
Valving split is sometimes expressed in terms of control ratio – the ratio between rebound and
compression damping, at a particular shaft speed. As a rule of thumb, a control ratio of 1.3 to
2.5 is pretty normal; <1.3 is somewhat bump-stiff; >4.0 is likely to jack down. Jacking is also
promoted by stiffer dampers, softer springs, or a bumpier track.
Tuning for a particular disturbance frequency is mainly a matter of making sure your natural
frequencies don’t match the excitation frequency. Since your unsprung masses and tires are
similar to the other cars’, this means using spring rates that don’t match theirs, or using stiffer
damping. Sometimes it helps to stiffen just rebound, but if you’re jacking down to the bump
stops you may be too far down that path now. Soft damping gives better roadholding, except
when the bumps excite the system at one of its natural frequencies. Stiff damping raises natural
frequencies, and also makes the system less frequency-sensitive.
You can also raise natural frequency by using somewhat stiffer springs than your competitors.
In the days of cart-sprung cars with primitive dampers, this was a major reason people sprung
race cars stiffly. Another approach is to run substantially softer instead. With everybody so soft
nowadays, that can be difficult, but if you add a sway bar and good bump rubbers it can work.

Finding a good combination is mainly cut-and-try at the track. Electronic data acquisition can
be a big help. I have an associate who specializes in that. His name is John Chapman. He’s in
Charlotte at 704-549-1309, e-mail jchap56756@aol.com. For shock dyno and build service, I
recommend Scott Munksgard at Munksgard Technical Services in Concord, NC at 704-782-
2611, e-mail MTSdyno@aol.com. He custom-builds Bilstein, Ohlins, Penske, and Carrera
shocks, and sells AFCO and Pro shocks and Afcoil and Hypercoil springs.

Sounds like you need an intense 1 on 1 session with sjmarcy.


EDIT:

And he told me he wanted to take a good look at your underpinnings.

Suspension tuning is endless, you cant just put 2+2 together and get 4 when it comes to suspension. You may want to change something at every different track, or with changing weather for example. I know there are some very knowledgeable people on here but hopefully someone is close to you and can drive your car at the track and let you know whats up, it sounds like you may need more rebound to stop the "Pogo"but your description is to simple for me to determine that adn it could be something else.

O sweet just saw that this was my 1,000th post!

I have a log for him.

700/400 RB front/ FM rear on the middle setting, about to go up to the stiffest setting. My corner balance is 200lb fat on the front left, and I don't know how bad that really is.

My car felt dialed in at TWS and HHR, which are two tracks on opposite ends of the spectrum; TWS is fast and I never go lower than 4th gear, HHR is tight ant twisty, I spend lots of time in 3rd. However at MSR-H, before the swaybar link broke, the car felt like a mess in "Sugar & Spice" but nowhere else on the track. I'm trying to avoid this when I hit MSR-C in a couple weeks.

Awesome, thanks for that link.

Has it been established that racecar setup can be fully encapsulated in one sentence with small words?

You are adorable.

STFU with your horse-shit or it will be another 3-months before you figure out that you're on global ignore because you're so accustomed to being ignored by all people in general, especially women.

I'll add something here in case you didn't already know.... you cannot adjust this except my moving weight around the car. This surprises a lot of people....

I get that, but do I adjust that balance with the spring or the sway?

A little of both. You want to run the softest spring possible while maintaining compliance. I prefer to use spring rates to balance the car in the big steps and sway bars for the finer adjustments.

sorry, been at work. lotta ?'s.

Thanks.
I need to stiffen up rebound damping on the "drive home from the track" settings at 4/2 from full soft.
I keep a notebook, now I need a pyrometer to add the right data to the mix.
I need to experiment more, I still have not cranked the rebound valving to "see what happens" yet.
The last track day was a waste due to the broken swaybar, I want to be sure I have my cards set-up right for the next race. The previous day at HHR I thought the car was wonderfull and had no complaints...this thread stems from my inability to hit Sugar and Spice hard.

I guess I should try the tightest sway-bar setting and see what it does, then go back to playing with valve settings. I need a damn test day rather than a race day.

...and the corner with all the weight is the corner that doesn't steer, correct? If my front left is heavy, could that explain why steady-state right-turns are a story of miserable understeer?

All other things being equal I think so, but there are alot of other things at play like alignment and stuff too. I really don't have that much experience beyond basic setup.

If you have pronounced and miserable understeer turning in only one direction, while the other direction feels great, you have something else going on.

not necessarily. if your corner balanced it should steer roughly the same in either direction. corner balancing doesn't mean the weights are gonna be equal at all corners. only that the lf & rr , and rf & lr are similar in weight.
which means you could have 150lbs. lf / 50lbs rr = 200lbs.
then 125lbs rf / 75lbs lr = 200lbs. and hypothetically have similar steering left or right. in this example the lf has more weight than any corner, but it shouldn't steer differently. what could, especially at that track cw, is higher temps from all the right hand turns. it could raise the tire psi, more on one side and that could affect the handling. on jakes car we ran 2psi less cold on the left and after the session they were all equal.

This Mark Ortiz stuff is awesome.

If you haven't already you should subscribe to racecar engineering, if for nothing else but the porn.


http://www.racecar-engineering.com/


This is supposed to be a very good book. A bit heavy on the maths, keeping your college texts nearby would be helpful.

http://www.millikenresearch.com/rcvd.html

Holy crap he's got a lot of information. I figured it would all be FWD stuff since they run Hondas but it's not. Definetely worth spending time looking through.

Mark's a Racecar Engineer / Consultant. I think those Honda guys are just storing some of his material on their site.

Seriously guys…at first some enthusiasts buy a cool car…many do some bling mods…a few do motor mods…some learn to drive…some modify the suspension…combinations. There are many ways to enjoy automobiles. If you get into track / autocross, it really pays to learn the fundamentals of suspensions and handling, keep records, try to improve your setup, datalog, make parts, video, read, discuss.

Miatadotnet is pretty much for everybody…CR more for the bling/slam crowd…this place (to me) seems mostly about the motor, engine, boost etc (which makes sense given the forum name and the interest of many posters). It's nice to see a few here showing interest in learning more about suspension and handling rather than the latest boost mod. After all…it's not hard to hold the gas pedal down ;)

Now…Mark is mostly used to dealing with experienced and pro drivers. I point this out because some enthusiasts leap to making all sorts of changes to their car to get rid of problems the car may or may not really have. You can really get lost if you go down that path. It's pretty common.

See…the driver can experience a car and then when trying to produce a good result may need to develop a driving strategy which may or may not be as expected. Since they will do things like take different lines, enter corners certain ways, give it up in other places than others. That's part of how the SM guys can produce quite decent lap time results on about any track.

So the point of this post is to yet again claim you know a lot and we dumb powerheads not only don't know much, but can't drive, and we should be glad you're part of this forum? Way to stick on topic.

Again, rather than contribute to the thread, he "listens to the sound of his own voice". He also fails to notice that roughly 100% of the fastest Miatas in the nation are on this board, and we didn't get here without fundamentals.

Go ruin a thread on M.net with this crap. Race Prep is sacred ground and you're incapable of doing anything except shitting all over it.

This section is mainly for those who run faster times than spec miata, and who think out side of the box, not those who drive what comes out of a box.

Have you tried this?
http://www.flyinmiata.com/projects/O...5/DSCN4844.jpg
http://www.flyinmiata.com/projects/OTC/race.php?day=5

You have to be careful with generalizing all right turns too. I spent some time trying to figure out why the black car wouldn't turn in for T10 at Laguna, until I realized that it was perfect everywhere else and T10 just naturally causes understeer from the terrain.

It is coming down T11 at Road Atlanta! :giggle:

Yes, my tears result from one corner. The difference is that 17-year-old children in $$$ SM's were trouncing me through here and I could not go fast on the rest of the track due to the tears clouding my vision.

What did you do to add some speed in this turn? Hotter entry and harder trail brake?

Yep. Move the braking point up ~75ft and ride the brakes the whole way through turn-in until it's basically over-rotated. There's so much camber in T10 that if you don't over-rotate on entry, you'll be fully hooked before the apex and pushing on exit. I got through there fast one time at my last Laguna day, and the steering wheel was straight the entire time.

So today, I read this and it blew my mind
http://www.eviltwinmotorsports.com/w...ter-2006.6.pdf :
I'm suddenly unsure which way to turn the rebound knob.

This feels applicable to my thread. Man, I'm getting to a point where sometimes I feel like I'm overdriving when I do stuff like this, but people like you agree it's faster. I do something similar at Hallett at #1 and #5, MSR-C CW through the triple apex, and now MSRH Sugar and Spice. This is specifically pertinent to Hallett where some of the DFW crew attempted to give me advice, while they're 5-seconds behind of course.

A damper's job in high shaft speed is to keep the tire on the surface, and in a perfect world over bumps with no change in load. What is the damper's job in low speed, glass smooth weight transfer?

I know low-speed compression is there to control roll to the magical number that works on every track, but what does rebound specifically do?

I'll ask questions later about the gray area between high and low speed, and the magical shim-stack transitions from high to low. This is getting scary, I may want 3-way adjustables soon.

Yup, I'd do the same. By getting more rotation earlier on such a turn, mid and and corner exit understeer and steering lock is reduced, and powerdown can be earlier. This is a key autocross driving skill too BTW. Combine with well timed throttle kicks for alien driving at those speeds. It helps alot to have good brake bias here.

:bowrofl:

This leans toward making my earlier point about the driver. After you hit a problem corner a time or two you need to come up with a strategy for more-good-less-bad the next time. It's mostly about corner entry and can sometimes involve making a judgement to turn the prior corner into a throwaway to setup the following more important turn.

If you geek out and datalog a few approaches for tracks you keep returning too, it will pay off.

Hey it is true whether you can accept it or not. It's an oft ignored aspect of Miata tuning. Ignore it at your peril and someone with a comparable car who pays attention will outrun you. Them's the facts Jack

BTW on the Morgans noted in the newsletter…these are pretty cool old cars. They are not much different from when they started being made countless decades ago. A frame partially made of ash…yes…the *wood*. The front suspension has the upright slide up and down on a pillar. Seriously. There are motorcycle engined thru V8 versions, three and four wheels, etc. Ahh the British…(I'm half Brit).

We get it, and that's why I have a Wilwood prop valve that I adjust regularly. I wish it had notches so I could dial in the settings for track conditions like I do for shocks.

AThere comes a point where someone is so annoyingly persistent and unaffected by criticism that we almost welcome you. "Almost" of course.

I looked under one of their racecars years ago hiding in someone's garage at the track to find that even on the leMans racecars, they have a wooden frame.

It should not be a surprise that most automakers that started in the early 1900's started with building horse drawn coaches.

The vette still uses a balsa wood composite floor pan.

You don't have to freak out about it. It's just basic stuff that is unfamiliar to some folks. Some noobs to track days think they have to *lower* tire pressures for instance. If you read my post, you'll note that it was noted as it IS in fact relevant. I didn't make a big deal about it.

https://www.miataturbo.net/attachmen...1&d=1298665484

On wood…note that some racecars deliberately use it on their undersides (even F1) as a wear surface for track/curb contact or due to rules. It's also used as a core between composite panels in other cases. Sort of like using styrofoam as a spacer.

You should be banned for posting that image and then failing to use tags correctly.


In other news, what racecars use wood as an intentional wear surface? I am only aware of it being used to enforce ride height rules.

http://www.joeharmondesign.com/

It's not that you're entirely full of shit. It's that you come off as a self important twat.

My datalogging group buy wasn't as successful as I had hoped (no doubt, due to forum ignorance and prejudice against those of us who use science), but I'm curious:

Would anybody be interested if I opened a group buy on wooden connecting rods (maple, I'm thinking), and possibly wooden anti-sway bars (most likely mahogany)? F1 teams use these materials, you know -- and it's a renewable resource, which is also a scientific thing.

Also in the works: data-logs (by which, I mean, actual logs).

new data logging pc
http://damncoolpics.blogspot.com/200...uter-case.html

What you posted in every thread is almost relevant. You spend more time pontificating on how much people don't know, rather than providing anything useful. this is true on here and the other board, you never post anything real, only rehtoric about old-school misconceptions. I challenge you to find a post on this board where you provided something other than a discussion on "misconceived misconceptions" you've halucinated, or I'll give you an e-wedgie and ban you for retardation. Look at this thread, you have half a dozen post and you've provided nothing for the good of the thread. Please, go back to modeling loafers on youtube, faggette.

lol @ sjmarcy's computer:
http://3.bp.blogspot.com/_mmBw3uzPnJ...er_case_04.jpg

as far as which way to go with the knob. it has been my understanding that the softest setting that still controls or stops unwanted or excess motion of the springs, gives you the most "mechanical" grip. where would you want it stiffer, theoretically giving you slightly less grip? where there are alot of high speed corners and the car feels too "sensitive" or unstable at high speed. in those cases, a little stiffer setting may help keep the car more stable, easier to drive, which in turns inspires confidence, which in turn could lead to faster lap times. some cars are fast, fun and easy to drive. some cars are just fast, which would you wanna drive? an extreme example of this is jakes s2k with big sticky tires and stock shocks/sways, it's not a good match. the grippy tires overwhelm the suspensions spring rates and valving. it's nervous handling, really touchy on turn in, and a little abrupt at the limit. it's fast, but it's a handful and nerve racking to drive (especially since it's not my car). his dad's miata on the other hand, has slightly less grippy tires, but the shocks/spring combo work well with the level of grip the tires provide. it turns in well, not spooky or overly sensitive, not too much body roll, easy to handle, smooth at the limit of grip, not choppy like the s2k. basically, like i've said with a lot of other stuff before, you have to experiment, and go with what feels comfortable to you. you went to hhr last week? why didn't you try different settings? it wasn't a race event. you can make 2-3 adjustments per session if you hurry or have a buddy change them in the hot pit lane. it only takes a few laps to see what difference was made.

Nope, I haven't been to the track since Houston. I wanted to hit ECR tomorrow but I has no turbonator bolts.