Howard Coleman

iTrader: (6)

Cam Worth (Pettit) sent me a set of his coil overs back in 2012 or early 2013 and since the price was right i sold my RSR s (to some lucky person) and swapped them in. my instinct was shouting at me that the 12/10 rates were going to suck but i was preparing for the Texas Mile in October and the rate would be just the ticket for 200 mph. i did the Mile and then the car was at Beyond Redline on the dyno for a couple of years where we went thru a series of slipping clutches, then a year and a half at another shop. exactly a year ago i welcomed my my FD home and have been continuing to work it. i am doing a bunch of road tuning and last fall i was heading up to see a friend in Door County and happened upon a section of road that was sectioned concrete.my back end, and probably the front end, was literally bouncing (as in up in the air) over the bumps.

as one who greatly respects the true racecar suspension engineered into the car this was the last straw.

double digit spring rates have NO business on an FD that maybe sees a track once a year. they do not belong on the street they are not dual purpose. if you are into almost no compliance on your suspension ontrack fine. swap them in when you go racing.

i have a distinct impression that there are loads of guys running way too much spring rate on their mostly street FDs. and probably not enjoying the drive.

you might be able to put a really big grin on your face for peanuts.

rather than buy another set of coil overs i removed the 12/10s, and added a set of Eibach 8 by 2.5 I D springs. they come in 25 pound per inch increments. i now run 475 front and 400 rear which is very close to the same rate (8/6) that was on my RSR setup.

Eibach makes a collar that adapts a 60 mm I D spring (often found on coil overs) to their 2.5 inch springs... 2.5 X 8 is a common race spring.

i run 18 X 9.5 front and 18 10.5 read w a Speedway Engineering hollow straight front bar.

the car is perfect for me, it soaks up rather than chatters over bumps, has a small amount of roll and is back to its old self. a true joy to drive.

ZDan

I've put ~25k miles on Ohlins Road and Track DFV coilovers since I installed them mid-2013. Initially I ran the "stock" 11kg/mm front and rear spring rates, but replaced the fronts with 13 kg/mm Swift springs in early 2014. The ride is unbelievably smooove over bumps. WAY better than the previous setup with 9kg/mm front and 7kg/mm rear Tein SS coilovers I had run for the first year I owned the car. I've tracked this setup at ~160mph at Mosport, 155mph at Watkins Glen. It *eats up* curbing without upsetting the car at all. Good stuff... On the street it likewise devours potholes and bumps with no muss, no fuss.

My car is a street car that I drive to and from track events. IMO, the 13/11 spring rates I'm at are a very good compromise between street ride and track handling.

If you were bouncing around on 12/10 kg/mm springs and all is now well on 8.5 kg/mm front and 7.1 kg/mm rear (aka 475 lb/in and 400 lb/in), I have to guess that you must have had insufficient damping to control the stiffer-rate springs. Damping is way way WAY more important than spring rate for ride/handling. Stiff springs with appropriate high- and low-speed damping will feel *firm*, but with good damping the ride can be quite nice without "bouncing in the air" over bumps.

BLUE TII

iTrader: (9)

Sounds like you have never been in a FD with Ohlins.

I just swapped my Ohlins back to the 100% stock suspension on my RX-8 because it was totaled (cosmetic) and was immediately reminded how it rode worse on stock suspension. More floaty as would be expected, but also more harsh over the little bumps, seams and gaps.

I had the same experience swapping to Ohlins on my FD. I had stock springs and GAB Super Rs and swapped to Ohlins and it rode sooooo much better. Those GABs were way overdamped and no highspeed blow-off.

Howard Coleman

iTrader: (6)

dampeners, no matter who makes them, cannot reduce spring rate.

11 KG is 11 KG.

my comments deal entirely with spring rate, not dampeners.

i of course have driven an FD w Ohlins. for the street it sucked. stiff kneed, no compliance. what makes the FD so different than most other sportscars is the dynamic camber gain in bump. it allows the suspension to work while keeping the tires in touch w the track. there is no need to overly stiffen it as you would w an FC or any other strut car or the typical double A arm that goes off camber in roll.

about a year ago i had a lengthy conversation w Ohlin/USA revolving around why they would

1. sell coil overs into the street market w 11 kg springs
2. why they had equal rate front and rear.

after a lot of back and forth the reason was that the rear damper body did not have enough length for travel w a softer spring!

OE FD springs are 4.69 KG/263 pounds/in front and 3.48 KG/195 pounds/inch rear

rear rate is 26% less than front. Mazda knew what they were doing. it is all about hooking up the back of a rear drive car and soft wins.

there is a middle ground where you can love driving the car all the time and go fast on the track.

8/6 or Eibach 475/400s are the middle ground.

just so we are clear i am making a case for the middle ground. if you like the other side of the bell curve have at it.

BLUE TII

iTrader: (9)

11/11 is the good middle ground in my opinion. They are Ohlins Road&Track after all.

11k is way to soft for the track. Track FD needs 16K to 18K.

I do concede that everybody has a different required spring rate to keep the tire out of the fender liner and the shock off the bumpstop though.

ZDan

Yes, and ride quality is still WAY more a function of *damping*. If you have spring rates that are too stiff for your dampers to deal with, you're going to have a bad time. Also if you have ***** dampers that have excessive high-speed damping, it's going to feel harsh over bumps no matter how soft your spring rates are.

??? Mine didn't... Are you talking about the DFV's or the previous version? Honestly I was not going to be able to live with my FD's ride on the street with the Tein SS coilovers (9k/7k springs) where I live. Very harsh over RI/SEMass bumps/potholes. The Ohlins DFV Road and Track coilovers transformed the car, fricking glides over road imperfections now.

??? Not in my case. My Ohlins have *remarkable* compliance over bumps. Way more compliant than my previous setup OR the quite good stock factory dampers on my AP1 S2000 or my '17 BRZ performance package (Sachs dampers).

Just about any double-wishbone or multi-link suspension sporty car will gain camber with bump travel, typically to the tune of about 1° per inch of travel. More than that would be undesirable, particularly with soft spring rates, as you'd get excessive front negative camber under braking. There's nothing magical about the FD's suspension geometry. It is very good, but it's not magical in this regard. Sure, strut cars don't gain nearly as much camber with bump, but still they usually gain *some* for most of their travel. Not the end of the world, you just have to dial in more static camber. No, they're not as good, but they aren't necessarily all *that* bad for performance either.

I tend to agree with you on the front/rear rate split, but IMO ~11kg/mm is actually a pretty good compromise between ROAD and TRACK for the FD.

The important thing is NOT spring rate, but WHEEL rate. FD front motion ratio is ~0.61 and rear motion ratio is ~0.69. With those motion ratios and the stock spring rates you give above, the wheel rates are 1.75 kg/mm front and 1.66 kg/mm rear. So the rear is actually only about 5% softer than the front, not 26% softer. Only very slightly front-stiffness biased relative to weight distribution, which makes sense for a *stock* factory setup for a *street* car for the masses.

With twice the power of a stock FD, I did want to move away from the stock square 11kg Ohlins spring rates, which given motion ratios results in rear stiffness bias. Based on my street and track experience I knew I would rather stiffen the front rather than soften the rear, so I went to 13 kg/mm front springs. 13/11 spring rate split results in ~4.8/5.2 wheel rate split, not too far off from front/rear weight distribution.

For my usage (~5k street miles and ~8 track days per year including time trials competition) I knew from the 9/7 Teins that those rates were way too soft for me, even on street tires. For me, 13/11 is a good "middle ground" running NT01 tires. For a serious track-only build on wide Hoosiers, I'd go quite a bit stiffer...
For street only, or for street + one non-competitive track day a year, yeah, I'd go quite a bit softer, probably close to the 8/6 range that is so often preached.

Every setup is a compromise, middle ground is a HUGE range...

Brekyrself

iTrader: (30)

ZDan, Do you have an excel calc we can plug in different numbers to see wheel rates? Curious what a 12k/11k setup would spit out for wheel rate split?

Good information in this thread, thanks everyone for the contributions.

Howard Coleman

iTrader: (6)

"For street only, or for street + one non-competitive track day a year, yeah, I'd go quite a bit softer, probably close to the 8/6 range that is so often preached.

Every setup is a compromise, middle ground is a HUGE range..."

i do agree that setup is a compromise and the middle ground, while not necessarily being huge is significant.

the question that is of most interest to me, raised by ZDAN, is the amount that the high speed circuit in the shock contributes to ride quality. i found 10s in the rear on my Pettit system not pleasant. was it the spring rate or the shock?

i owned both a shock dyno and a digital spring rater for a number of years so i dusted off my data to see what i could learn.

most dampeners/shocks have 3 circuits. valving differs in each of course, both the amount and the curve. in this thread the primary interest is in dealing w the high speed circuit which relates to bumps. the nature of the high speed circuit, as far as dampening, creates the general sense of "ride." ride as in the real world as in on the street. slow speed relates to sweeping turns.

dynoing an adjustable shock takes time as you dyno at all 16 or whatever number of adjustments and you dyno each adjustment at 9 force levels... then record all the data for compression and rebound.

the high speed setting on my dyno applied 300 pounds.
the time is measured for the shock to move 2 inches.
faster movement of course indicates less resistance
i used a shock heater to duplicate real world conditions.

rear shocks

FD/OE............................................ 18.8 inches per second................................... matched against the 195 pound/3.48 KG
RSR (rebadged Tein HA) full soft.........10................................... ...............................378/6.75
GAB full soft....................................15.3

as you can see the stock shocks offer significantly less resistance than the Tein which is appropriate as they are designed for a softer spring.

i no longer have my dyno but would be interested in the speed of other dampeners measured at 300 pounds.

which brings me back to my original observations re my current 475/400 setup that, for me, is perfect.

as mentioned in my first post my car was hopping over sectioned concrete pavement w the Pettit 12/10s. full soft in the rear and 40% from full soft front.

255/18/9.5 wheel front at 30 psi and 295/18/10.5 rear 27 psi set cold.

after swapping in the softer springs the car felt just a tad floaty in the rear. i reset the rears to 40% from full soft and it is now perfect for me. that indicates that there is not an excessive amount of jounce dampening in the Pettit item.

if the dampening was my problem, running the 10s in the back, it would have continued to have been a problem w the softer springs... instead i had to increase the adjustment.

it is great to have a suspension again.

my second comment w re to 475/400 deals w the track.

during the time i ran the RSRs which were very close to the same as my current rate, i ran four Ferrari Club of America weekend track events at Brainerd Int'l Raceway. Brainerd is on the CENDIV SCCA National calendar and i had the GT3 track record for a number of years and won numerous races. the main straight is 6000 ft long and you enter it around 60. turn one is banked, wide radius, 90 degrees and you almost don't have to lift... turn 2 is exactly the same radius but flat. you want to be right in turn 2. the rest of the 2.5 miles is your typical 3rd/4th gear stuff.

i was running shaved Toyo Proxes... (this is back in the day 95-2000)... big brakes, not a lot of power, racegas... i drove my car from the Milwaukee area, somewhere around 400 miles each way...

not one car ever beat me. no one was on race tires, but there was just about every car you could imagine there. the closest car to me was a beautifully setup up Porsche 944 w a really built roll cage and a monster KKK turbo.there were places he would gain on me so i pitted, checked tire temps and changed my camber a bit and in the next session the big red 944 behind me slowly turned into a red dot.

this is on my 432/7.7 F, 378/6.7 R springs.

Granted if you are on race rubber the game changes... as i said at the beginning, this setup works for me and i now, again, love driving my car every minute. it may work for you.

j9fd3s

iTrader: (3)

it is about 90% the damping, 10% the spring.

we know this, the spring controls how far the suspension moves over a given bump, the damper controls the speed it happens.

we put Ohlins on the race car a few years ago, and it was like magic, they handle well, you can do over curbs and berms without upsetting the car, AND it rides better than stock. this is with 1100/750 springs in a 2300lbs car (miata).

my personal FC is running 8/6 springs. with a set of AGX shocks, the ride was intolerable, it currently has a set of Teins on it, and it rides much much better, although its over damped instead of being way under damped.

i have been thinking about putting softer springs on it (with different or revalved shocks) just because it doesn't pitch or roll, and i like that in a street car

mrselfdestruct1994

iTrader: (1)

I went from 8/6 Bilsteins to 16/16 Ohlins and on rough roads the ride is harsher. Smaller bumps and ruts are fine, but the reduced suspension travel makes big bumps and depressions more jarring. I prefer the Ohlins overall but the Bilsteins were good too.

Howard, may I ask what are you running for bump stops?

Howard Coleman

iTrader: (6)

bumpstops are not modded and i have yet to contact them at 25 inch ride height.