ptrhahn

iTrader: (9)

Howard's suggestions on spring rates are also for combo street/track cars running street tires.

Once you're running R-Compound tires, you'll need more rate—you'll be going faster, and soft rates will make the car rub, feel sloppy and slow to react. Heck, I was tearing up fender liners and hitting the bump stops on 500/400 rates with koni's on street tires.

Depending on your style too, you may want to push the rear rates closer to the fronts than the stock ration would suggest, because you're more comfortable with a lively car.

I'm up to 700/600 with Hoosiers, and probably need to bump up to 800/700 or 800/800 with JRZs. It's all about trade-offs

Many_107060

ok

Howard Coleman

iTrader: (6)

was nosing around Koni's site and bumped in to this. hey, what does Koni know about chassis tuning...


"Suggested Adjustment Procedure for Road Course Use

Adjusting the Compression (Bump) Damping Control

Bump damping controls the unsprung weight of the vehicle (wheels, axles, etc.). It controls the upward movement of the suspension such as hitting a bump in the track. It should not be used to control the downward movement of the vehicle when it encounters dips. Also, it should not be used to control roll or bottoming.

Depending on the vehicle, the ideal bump setting can occur at any point within the adjustment range. This setting will be reached when "side-hop" or "walking" in a bumpy turn is minimal and the ride is not uncomfortably harsh. At any point other than this ideal setting, the "side-hopping" condition will be more pronounced and the ride may be too harsh.

1. Set all four dampers on minimum bump and minimum rebound settings.

2. Drive one or two laps to get the feel of the car.
NOTE: When driving the car during the bump adjustment phase, disregard body lean or roll and concentrate solely on how the car feels over bumps. Also, try to notice if the car "walks" or "side-hops" on a rough turn.

3. Increase bump adjustment clockwise 3 clicks on all four dampers. Drive the car one or two laps. Repeat this step until a point is reached where the car starts to feel hard over bumpy surfaces.

4. Back off the bump adjustment two clicks. The bump control is now set.

NOTE: The back off point will likely be reached sooner on one end of the vehicle than the other. If this occurs, keep increasing the bump on the soft end until it too feels too hard. Then back that side off two clicks. The bump control is now set.

Adjusting the Rebound Damping Control
Once you have found what you feel to be the best bump setting on all four wheels, you are now ready to proceed with adjusting the rebound damping. The rebound damping controls the transitional roll (lean) as when entering a turn. It does not limit the total amount of roll; it does limit how fast this total roll angle is achieved. How much the vehicle actually leans is determined by other things such as spring rate, sway bars, roll center heights, etc.

It should be noted that too much rebound damping on either end of the vehicle will cause an initial loss of lateral acceleration (cornering power) at that end which will cause the vehicle to oversteer or understeer excessively when entering a turn. Too much rebound control in relation to spring rate will cause a condition known as "jacking down." This is a condition where, after hitting a bump and compressing the spring, the damper does not allow the spring to return to a neutral position before the next bump is encountered. This repeats with each subsequent bump until the car is actually lowered onto the bump stops. Contact with the bump stops causes a drastic increase in roll stiffness. If this condition occurs on the front, the car will understeer; if it occurs on the rear, the car will oversteer.


1. With the rebound set on full soft and the bump control set from your testing, drive the car one or two laps, paying attention to how the car rolls when entering a turn.

2. Increase rebound damping three sweeps or 3/4 of a turn on all four dampers and drive the car one or two laps. Repeat this step until the car enters the turns smoothly (no drastic attitude changes) and without leaning excessively. Any increase in the rebound stiffness beyond this point is unnecessary and may in fact be detrimental.

EXCEPTION: It may be desirable to have a car that assumes an oversteering or understeering attitude when entering a turn. This preference, of course, will vary from one driver to another depending on the individual driving style."


thank you Koni and thanks for your aluminum double adj shocks i ran for 6 seasons on my GT3 RX3. the bold above is me BTW.

howard

jkstill

iTrader: (11)

Howard, if you can share the URL for this article on the Koni site, it will save a bit of searching.

jkstill

iTrader: (11)

Here it is: Suggested Adjustment Procedure for Road Course Use

ArmenMAxx

iTrader: (21)

Howard,

Given that you ran/run the Pettit Track Pro stage 3's, I have a question for you.

Did you have issues with lifting your inside front tires? I am running the stage 3's 12k 10k rates WITH tanabe front/rear swaybars and she still is lifting the front tires more than I want. Im sure its contributing to my understeer issue and turn in as I am seriously losing some tire contact. My ride height is about 25inches. Car is beautifully corner balanced at that height and I am running about -2.5 camber front. -1.7 rear which I am very happy with. 275/35/18 tires rear, 265/35/18 front (Dunlop Zii's which are phenomenal)

The way I see it I have a few options to work this out. Your opinion will be valued.
1) Lower the front- Problem with this is my car leans so much that I may start to rub inside the fender.
2) Less front camber? May increase contact of the inside tire but it will def be counter-effective and cause more understeer.
3) Make the rear shocks considerably stiffer vs front. If the dampening is stiffer, itll lean down slower thus lift the front inside tire more gradually/slowly. This is an easy experiment to do once I get a change to drive the car soon and track it within a few weeks.

Here is a picture after a braking zone entering a high speed swepper. The inside lift is more dramatic during other slower/tighter turns.

Howard Coleman

iTrader: (6)

sorry ArmenMAxx, i will try to be of help on this tomorrow... although by now you probably have fixed it.

howard

Howard Coleman

iTrader: (6)

i don't see tire temperatures.

tire temps and pressures along w travel indicators will lead you to the solution.

there could be numerous factors contributing to your push and possible dynamic over-travel.

pls post your starting tire pressures and pressure after 3 to 5 laps.

please post your tire temps after 3 to 5 laps.

we will then get tuning.

howard

Zepticon

iTrader: (1)

Howard, do you have any experience with the Öhlins coilovers? The Road & Track DFV, given that one change the springs to something softer? They make the shocks on the Koeningsegg, so one should think they know their stuff.

FD3S: Ohlins Road & Track DFV Coilovers - SakeBomb Garage LLC

ArmenMAxx

iTrader: (21)

Depending on the track temps, tire pressure begins anywhere from 23-28psi cold. End up with 34psi hot.

Before I usually aimed for ~2psi less in the rear vs front. Now I run about same front and back to address the push.

Howard Coleman

iTrader: (6)

"do you have any experience with the Öhlins coilovers?"

no.

i will say that a few years ago i sold my shock dyno and a number of new products have appeared so speaking comparatively re valving i am not your info source.

that said, it appears that the coil overs you are looking at come w 11/11 springs. the most important component to get right when choosing a coil over is the SPRING RATE.

rear rate should be no more than 80% of front. ideally 75%. front engine rear drive cars do not balance out at 50/50. the rear needs to stick and be more compliant. if you run equal spring rates you will be loose and never be able to hook up the rear. in simple terms you will have to wait longer in the corner before being able to press on the right pedal.

if you do trim the car out w 50/50 springs you will have screwed something else up to gain the balance.

an example of a typical tuning mistake... if your car is oversteering (sliding in the rear) the error would be to stiffen the front to gain balance but what you would have done is decreased overall chassis grip.

the solution is to work on the end of the car that isn't working.

equal rate springs probably work well for drifting but not for road racing.

i personally feel that valving on coil overs for most apps is way over thought. since i owned a shock dyno for a number of years i know.


"Depending on the track temps, tire pressure begins anywhere from 23-28psi cold. End up with 34psi hot.

Before I usually aimed for ~2psi less in the rear vs front. Now I run about same front and back to address the push."

as i have often posted, if you are tracking your car and care about going fast you are BLIND without a pyrometer.

100 bucks buys you eyeballs

Amazon: "tire pyrometer"

tire temps not only set your camber at all four corners, point you in the accurate direction as far as overall trim but also allow you to exactly set tire pressure at all four corners of the car.

combine it w a tie wrap on your shock rod and take numerous seconds off your previous best lap time.

howard

ArmenMAxx

iTrader: (21)

Pyrometer is most certainly an essential tool for those serious about tracking their cars. This is why Ive been using one for years now. Along with chalk, photoanalysis, etc I pretty much have my alignment and tire pressure addressed.

My issue is beyond camber & tire pressure, its without doubt suspension. The front lift of my tires is a key issue which I am not certain how to address. Short suspension travel of the pettit coupled with its limited ride height adjustability is prob the culprit. I plan to add 12k rear springs by fall and see how it goes.

Howard Coleman

iTrader: (6)

O K, I am with you.

assuming you have that covered inside front wheel lift comes from too soft rear springs. other factors enter in but things like roll centers etc are fine...

HC

ArmenMAxx

iTrader: (21)

Appreciate it Howard. Ill post back with some before/after pictures.

thatkid2007

iTrader: (2)

sweet pics

Quik 93 FD

Maybe this has been addressed but how are you measuring ride height "at the top of the wheel well" ? As in, with or without the tire/rim to the spot in the center of the inside of the wheel well? I'm about ready to align the car for the first time since putting it back together. Cusco coil overs, 275/40/17 back tire.

Howard Coleman

iTrader: (6)

outer lip above the wheel center

Tem120

iTrader: (5)

Here is a difficult question I think when it comes to our car ..

I have a few sets of springs to play with , and other tools I can use to stiffen or soften my suspension

Right now I have it set up quite soft . On hard bumps I sometimes hit the bumpstops , BUT this gives me really good traction .

And I started thinking about something .. WHAT is the ideal suspension travel for our cars since we have un equal length double wishbones / multilink

Which makes us gain camber as more suspension travels on a hard turn / hard acceleration .

Do you want as much travel without hitting the bumpstops aslong as the car's characteristics remain neutral ?

$lacker

iTrader: (9)

I've heard the answer is 2"

KevinK2

I had an issue with front lift on a Porsche 924T (used) that I had just put big bars on for the track, and the front bar was just too big. When I put a jack under the chassis on the left side of the front, the bar would prevent any travel in the front suspension, no extension on the left side, no compression on the right side.

I cured the problem by buying my 93 FD (off lease), and carefully selecting bars I could put on for the summer track season. I used a method of weight tranfer analysis published by racer/engineer Fred Puhn, which is consistent with Howard's tips .... except Puhn includes the unsprung weight in figuring out the total weight transfer, and it's bias. I think Howard forgot to mention this.

About your problem, it is either too much roll stiffness in the front, or lack of front suspension travel .... in compression on the outside tire, or extension on the inside tire, on the corner where you experience lift. Front end lift should be avoided because it ends the LINEAR weight transfer process at both ends as the G's increase (I know rear end lift is ok on fwd autx cars). At that point all additional weight tranfer happens at the rear only, and the roll center rises increasing rear end weight transfer.

Looking at the picture, it looks like you are into the fast sweeper, based on looking at the partly unloaded inside tires. It also appears you have too much neg camber up front, and the rear could use a little more neg camber, if any. I'm not sure you can detect this with tire temp's taken in the pit.

Since you feel you are still understeering, with added rear weight transfer, it could be an Ackerman effect where you get added toe-in, with a tight corner.

KevinK2

Speaking of sway bars, here is a dated list of what WAS available, and the % increased stiffness vs oem. I ran the Eibach hollow bars, and cracked the rear when I set it on stiff. And I had thought I was messing up toward the end of that day!

Antiroll Bars

ZDan

Short

Also have to consider the motion ratios. It is the WHEEL RATES that are important, spring rate doesn't tell the whole story. Wheel rate is spring rate multiplied by the SQUARE of motion ratio, so actually the motion ratio is the bigger driver.

The front and rear spring rates will be different for different cars. What works for the FD will not work on something like an FR-S/BRZ (very different motion ratios).
A lot of ~50/50 weight distribution FR sports cars do have 50/50 or even more rearward-biased *wheel* rates.
Stock 240Z spring rates were 80 lb/in front, 100 lb/in rear, front/rear motion ratios ~0.90, giving wheel rates of about 65 lb/in F and 81 lb/in R, decidedly rear-biased. Mine handled great with 2x stock spring stiffness, same rear-bias.

AP1 and non-CR AP2 S2000s have stiffer rear springs than fronts. But again, you have to account for motion ratios, which are 0.70F and 0.67R on that car. It works out that the AP1s have stiffer rear wheel rates (46F/54R), AP2s have pretty much the same wheel rates front/rear (51F/49R).
It's worth noting that a lot of the handling issues with the AP1 are related to rear toe change with bump, more so than rear stiffness bias (I track an '01 semi-regularly). Basically, the rear stiffness bias makes it easier to get the tail out, at which point the uninitiated driver will LIFT off the gas which unloads the rears *and* causes the outside rear to toe relatively OUT. Instant spin...

The stock FD is really only *slightly* front-stiffness biased. It needs somewhat stiffer front springs because the front motion ratio is a lot lower than the rear motion ratio.
FD's stock spring rates are 263 lb/in front, 195 lb/in rear, and motion ratios are ~0.62 front, ~0.70 rear, so the stock wheel rates are:
263 lb/in * 0.62^2 = 101 lb/in front
195 lb/in * 0.70^2 = 96 lb/in rear

So wheel rates are ~51/49, not far off of 50/50.

I totally agree that 50/50 *springs*, *given the FD's motion ratios*, is not a good solution. The Ohlins setup with 11k/11k, or 616 lb/in springs, results in wheel rates of 237 lb/in front and 302 lb/in rear. 44/56 front/rear stiffness distribution.
I ran this setup, and had to disconnect the rear sway bar to get power down.

I recently put 13k (728 lb/in) springs up front, so now I'm at 280 lb/in front, 302 lb/in rear wheel rates. Still rear-biased, 48F/52R on my 50/50 car.

I also went stiffer on the front Speedway bar and re-attached the rear bar.
Hooked up pretty well at Thompson Speedway a couple of weeks ago, but with 500+hp I think I might still need to disconnect the rear bar!

Not necessarily... Adding stiffness doesn't just take away grip at the outside of that end of the car, it actively GIVES more grip to the outside tire at the other end of the car. What you do at one end affects the other. If the car is relatively softly-sprung, I'd stiffen the end with grip. If the car is over-sprung, I'd soften the end that needed more grip.

In my case, I know that 11kg/mm is a bit soft for road course work on R-comps, and I was grounding the front splitter at turn 3 in New Hampshire and rubbing the fender liners as well even on street tires, so I went with stiffer front springs rather than softer rears.

For someone ordering the Ohlins for the street, I'd change the rear springs for either 8 or 9kg rears to go with the 11kg fronts. For more track-oriented, swap 13 or 14kg front springs in to go with the 11kg rears.

KevinK2

I agree about considering spring rates at the wheels. But you did not mention that sway bar rates must also be treated the same way, and for the stock FD, they could be more significant in the front vs the spring rates.

My 93 has the stock suspension on it now, with the larger rear bar. When pushing near the limit at 60mph on a 270 deg 30mph on-ramp, up-hill, the back end wants to come out and it is not a good feeling, with guard rail 6 feet away. When I set rear tires 4 psi higher than the front, it is much more balanced, and a bit faster.

.

ZDan

That is another relevant topic. But primarily I wanted to point out that spring rate, by itself, doesn't tell us anything. You have to consider the motion ratios to know what is really going on. The reason stiffer spring rates up front works so well on the FD is that the front suspension has more leverage against the spring than in the rear. The front springs need to be 27% stiffer than the rears to have the same wheel rates all around. Or looked at the other way around, the rears should be 78% of the stiffness of the fronts for "even" wheel rates.

Of course setups can work well with somewhat stiffer front or rear wheel rates, but that's the ballpark you want to be in on a 50/50 FR car.

Definitely shouldn't be driving anywhere near cornering limits on an on-ramp on the street! Tracks usually have a fair amount of runoff
Driving a well-balanced car requires commitment. If you find yourself going too fast for comfort around a curve and LIFT, bad things ensue...

Also, might see how you like it with the rear bar disconnected, but I think a stock-suspension '93 should handle fine with proper inputs at the helm...

Fritz Flynn

iTrader: (263)

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