smg944

iTrader: (34)

finishing up my fc im looking into the isc racing coilovers. the spring rates are 8k front and 6k rear. i am also removing the rear sway bar. just looking to see if i should raise the spring rates? the car will be used on road coarse and some auto-x. thanks for any imput.

rob81gsl

iTrader: (3)

the 8/6 is pretty weaksauce for the track but will prob be better for the autox. im not a cone chaser myself so that is my assumption. but im using 12/10 on the track and i need to go stiffer. and far as i can say from my experience throw that rear sway bar in the weeds. i could never get power down with that thing on.

TrentO

I'm not sure I agree with the high spring rates. In last year's indy support race one of the fastest cars was a road course stock car with a very soft setup. The track had a few bumpy bits, but mostly pretty smooth and pretty high traction. I'm running 550 (633 kg) from and 425 (489 kg) rear in my FC and the car is pretty planted with the yokohama slicks. I can blast through most corners at full boost 14lbs (about 400 rwhp) and it just hooks. If I went stiffer I think I'd lose grip and the car would loose the rear around the longer corners. In my opinion the suspension's job is to make optimal use of the tires, in order to do that you need to control the contact with the surface and control the weight transfer of the car. A softer car usually does a better job of the first point while a higher spring rate car usually does a better job of the second. I also beleive there is a limit to the benefit of transferring weight to the inside wheel as the camber i positive to the turn direction anyway so you are using a much smaller contact patch. I'd rather go with Herb Adams thinking and run as soft as I can wihtout bottoming out and attempt to control the weight transfer using the swar bars. With that all said, my suspension still requires some work. I'd really like to raise the front mounts on the rear suspension trailing arms to add some anti-squat as I can currently bottom the car out on a hard right hander under full boost (I've added some shortened bump stops on the shock to prevent catastrophic shock bottoming). If I were you, before I start talking spring rates I'd really think about what I'm trying to fix. Give Tony over at AWR a call and talk to him, if I recall correctly he ran a pretty soft suspension in his E-production car to good effect.

cheers,
-Trent

Black91n/a

^+1, 12/10 is crazy stiff. I run 7/5 springs on Tein Flex coilovers with a Racing Beat front and stock rear sways and it handles pretty well I think. I've had driving instructors comment that the car handles quite well, so it must be good, they've felt many setups over the years. I've never felt it to be too soft and it could do with being softer over rough sections of track, so I'd be hesitant to go much stiffer at the moment, at least on the tracks I go to. I'd definitely reccomend that as a good starting point for a car that still sees street use. I've still got the full interior, so I've got more rear weight bias than a racer probably would with no interior, so that changes things a bit. I may end up ditching the rear bar once I strip the car.

smg944

iTrader: (34)

thanks for the imput guys. i am also looking into the bc racing coilovers. from what i hear they have great service for repair items. they are also 8k front 6k rear.

kwerks

iTrader: (2)

Its depending on the track you run, speed, how much aero you have, what tires are on...etc...I see guys using things from 8kg/mm to 20kg/mm with everything based on the before list.

gkmccready

My car is still sitting on the 400# front, 275# rear that MazdaComp recommended in their good ol' 1997 catalog. They were working really well when I parked the car and they'll be my starting rates when it comes out of hibernation. I may replace the Eibachs with Hypercoils, though...

Does anybody know the motion ratios for the FC suspension? I'm curious what the wheel rates look like.

j9fd3s

iTrader: (3)

there is a post about the motion ratio's in the suspension section, it comes right up in a search

gkmccready

Thanks. I'm still figuring out which areas of this forum have the information I'm after. The posts I found seemed more like the typical "assume the mac strut is 1:1" but another said it's about 0.95. Either way it's interesting.

My Corvette has an MR of 0.69 in the front, and 0.55 rear, the shock angle comes in to play for wheel rate on the Corvette at about 65deg front, and 55deg rear. I'm running 475#/575# coilovers on it which works out to about a 200# wheel rate front and rear. It's funny the Corvette at 3400# would run a softer wheel rate than the RX7 with so much less weight.

j9fd3s

iTrader: (3)

dunno about the vette at all, as its not just weight/wheel rate but suspension geometry and the sway bar, tires, intended uses...

as an example our current integra, @2450lbs and 600F/1100R is a little soft on a roadcourse, but its totally unstreetable, a normal road just launches the thing...

that being said 400/275 is really in the ballpark in the FC, going stiffer (or softer) would have more impact on how the driver feels than it would on laptimes

ajhehr

sorry to chime in late, There are way to many variables on the worksheet that arnt discussed here.

rule of thumb. you want to run the softest springs with the most travel possible, while maintaining as much inside and outside contact patch possible. this allows you to still maintain control of your car during bumps, curbs, and +g situations. Stiff springs will cause the car lose contact completely with the ground or rebound tremendously off of transitions, this means that the driver will have to regain control of the car(if you haven't crashed out yet) before continuing to drive. this costs lap time... every lap. every corner, I think it is 6 inches off the apex is a tenth of a sec.?

many people go crazy stiff on springs and get better track times because they haven't set up their car well and it acts like a band aide. also most shocks are not capable to handle road racing well, including most if not all off self coil overs.

suspension is not an exact science, it is an art. My friend who has a 944 likes his car set up so loose that I almost spin out just backing it out of the shop. My 7 is set up tighter,so that you have to beat the crap out of it to get it to turn a fast lap, and you allways have to turn on the gas...

it depends allot on you, and your setup, and what you like.

start looking for a skid pad now. keep the rear sway (its a balance tool), you dont have to have it connected, but hold onto it.

PERSONALLY the best things that have helped me in the my FC were (in order)

-BIG ***** AND NO COMPASSION FOR THE CAR
-LOTS OF SKIDPAD TESTING
-Kazz 1.5 lsd
-stance coil overs (i love these cheep bastards) gr+pro ss, (9k, 7k springs)
-spherical bearings EVERYWHERE!
-Sparco evo3, smaller steering wheel (I am comfortable and dont beat the crap out o myself) deleted the armrests.
-275's and 315's


at the end of it just make sure you have fun! both in the prep and at the race.

Black91n/a

There is a big caveat with FC's though, that's the strut front suspension. Due to the compromized dynamic alignment, where the outside tire looses camber as the car rolls, the front needs stiffer springs to try to minimize the body motions to maintain a better contact patch. Along with that we must run more static negative camber to compensate which lessens the tire's grip in braking.

On a side note, how hard was it to fit an Evo 3 in an FC? I know fhey fit me well, but I wasn't sure I'd be able to fit one in the car. I'd love to see any pictures and get any details that you'd care to share.

ajhehr

it sucked. took me 2 days to get the spot correct.

I used the steel side mounts and then made a plate (square) and welded nuts to that so that bolts would be threaded through the side mounts and into the plate,
I then located the seat and welded the plate to the car. after removing everything that was in the way... it was the only way to get me in there... i also raised the shifter about 2". and moved the steering wheel 5" towards me.

Its REALLY nice now. but took a crap load of work.

the breaking thing gets me to... I raised the back of the car up some, and am running low tire psi's, im about to install the tilton pedal assembly to try to fight it a little more.

edit* i dont think I have any pictures other then finished pictures so im not sure how much it would help...

Dan Unk

iTrader: (7)

If you don't mind, post the pics of the finished install, I want to see how it turned out.

edmcguirk

Just to throw in some late comments, I started out with relatively soft springs because I agree with the idea that you should go as soft as you feel comfortable with.

I started out with 350F/250R and ST sway bars front and rear. That ended up requiring 5 to 6 degrees of camber to get good tire temperatures. I don't auto-x that car much but those spring rates gave me reasonable transition times when trying to run a good slalom (you don't have to wait long for the suspension to transition from full right to full left). However when the car is leaning approximately 5 degrees, the inside tire has approximately 10 degrees positive camber. I did run into some problems burning the inside edge of the rear tire. (I used to set my rear camber about the same as the front, the tire temperatures were good but since the camber gain of the rear suspension is greater than the camber gain of the front suspension, I believe that the rear camber never needed to be that steep)

After seeing those problems with the inside edge of the rear tire for a few years, I decided to stiffen the spring rates and I chose 450F/325R. That allowed me to drop my camber to 3 degrees and the problem with the worn out inside edge of the rear tire went away. I get very good tire temperatures and very good tire wear. (even in a 4 hour endurance event)

Now my only problems are a slight delay of the rear tires taking a set when transitioning from right to left as I go up the esses at Watkins Glen which I believe is caused by the fact that I am still running the same camber in the front and back and also fine tuning my rear toe.

I have been taking a sabbatical from racing and I need to get back.

Oh - btw - My track car is still technically street legal and even though I only drive it to the race track, I don't have any trouble with 450F/325R on the street.

gkmccready

Any thoughts on changing the rates if I go to an 18in wheel? The new Hoosier Radial slicks are looking pretty good...

j9fd3s

iTrader: (3)

really hard to say, as there are many factors.

18's are BIG, i would think getting them to fit would necessitate a low profile, the tire also has a spring rate. a big low profile 18, should be different than a 245-45-15. but they also should increase grip, and more traction = more weight transfer

we've gone past the point on the honda where we're actually exceeding the body's strength, upon disassembly, its really clear stuff is bending and flexing. we are also popping spot welds.

the FC is built better than the honda, but still at some point the body is a weak link, and needs to be stiffened

so i don't have any specific recommendation, except that different tires need testing.

gkmccready

It's been suggested to me that something closer to 500# front, 350# rear would be better but there's also concern about those being out of range for the KONIs I currently have on the car.

And, yeah, the 18s will be big. Thinking along the lines of a 285/645r18 and 305/645r18 ... hoping the jgrewe fenders will swallow the big meats. :-) They'll be about half an inch taller than the stock 205/55r16 which'll hurt gearing, but should help get the power down. Even if I end up running a Hoosier DOT-R instead of the slick that's about the height of them to get the big boys.

Curious about the weight of a typical EP wheel+tire... if I do an 18x12 CCW Classic the wheel is about 21# and a 335/35r18 A6 is probably in that same range...

SCCAITS

iTrader: (3)

The Hoosier 9.5" EP slick is 18lbs. The 15x7 can vary obviously with the circle track wheels in the 17-19lb range approx or some aluminum rims down to 13lbs or some custom stuff probably even lighter. I'd say 31-35lbs is a good average range.

gkmccready

Thanks! The 285/645r18 and 305/645r18 radial slicks are 27# and 28# on their own! A CCW Classic in 18x12 is 21#. So you're pushing 50# instead of 35# ... significant.

Would the higher unsprung weight be more of a shock valving, or a spring rate change?

jgrewe

iTrader: (1)

Unsprung is all compression valving, nothing to do with holding the car up with the springs.

gkmccready

Am I converting the 8k/6k numbers correctly?

8k kg/mm = 8000 * 2.2lb / kg / mm = 17600 / 25.4 mm / in = 693#/in ? I ask because I can't make heads or tails of them compared to lb/in. :-) Especially based on TrentO's update where the kg numbers don't make any sense to me at all, but the 550/425 does... if my math is right those would be considered 6.5k/5k ?

gkmccready

Thanks. One of the locals had me confused saying we'd have to spring the car for the heavier wheels and my brain just wasn't grokking that.

wrankin

Nope, but close.

8k = 8kg/mm (not 8000 kg) = 8 * 2.2 lbs/mm. = 8 * 2.2 * 25.4 lbs/in.

= 447 lbs/in.

the conversion factor is 55.88

gkmccready

Knew I should have written down the units on the whiteboard rather than doing it in my head. :-) Thanks. I must really need coffee if I was thinking 8000kg/mm made any sense at all. Some days... thankful it's vacation soon.