eoph

I am a little confused. Because it was said you want more rear weight for traction, but having more weight transfer to the rear is not good for traction?? I am also confused about the spring rates. If i could get the roll resistance as stiff as possible then I could lower my spring rates for more traction??

sarukun

Eoph,

I believe he meant total roll stiffness, which is a combination of the roll resistance from the springs as well as the anti-roll bars.

Say if you're running rather hard springs with a standard arb and find that the car is uhm, doesn't handle bumps too well, you can drop your spring rates and go to a larger arb to retain the overall original total roll stiffness.

As Howard Coleman also mentioned, the arb's two tasks are to control roll and to tune for oversteer/understeer tendencies of the car at the limit. Or some people like to call it steady state.

Do correct me if I'm wrong.

Cheers

wptrx7

Did you ever experience his?

Eggie

Thanks for the info, Howard. It prompts a few questions.


Stock rear springs are 74% as stiff as the fronts. Your rear springs are relatively higher at 87.5%. Doesn't this go against your motto of keeping the rear soft for better traction? It appears that your recent ARB changes support this, as you've increased the front bar more than the rear, restoring the balance. Were you getting too much oversteer with 432/378 springs and stock bars? If so, under what conditions? Did your stiffer front shock settings mitigate this during turn in & initial roll? Other tuning tips this should introduce?


May I assume that R-package shocks showed different results than non-R models? If so, do you prefer one type for road-course use? Different spring recommendations for each?


Hot or cold?


Caster lifts the outside front tire and lowers the inside. Doesn't this reduce weight transfer across the front? Therefore more weight must transfer in the rear. Okay. I think this should reduce understeer and encourage the rear to rotate during corner entry. As we apply the throttle and reduce steering angle, caster will contribute less and less oversteer until the corner is completed. Correct analysis? If so, why is this bad?


Many thanks! This stuff is complicated...

AMRX7

Too much caster can actually reduce weight on the inside rear, which isn't a good thing for traction.

I run 1000F/800R springs and a relatively large front/small rear swaybar setup for autoxing. Softer spring rates didn't cut it with the 315F/335R Kumho V710 tires. I had to keep going up up on the rates to keep off the bumpstops. If you are getting on the bumpstops you'll end up chasing that handling problem and then be totally off once you fix it. As Howard said, the zip tie on the shock shaft is an easy way to see what your max bump travel is.

Also, on camber with the Kumhos, I run over -2 degrees both front and rear. The FD suspension does a great job with camber curves, but the grip and structure of the Kumhos want significant negative static camber or you end up with much too high outside temps.

-Andy

Eggie

Thanks, Andy. I'll take an F for incomplete analysis above! Funny thing is that I knew this stuff 4.5 years ago...

kf3er

iTrader: (1)

Howard,
I'd like your thoughts on the OEM torsen diff for road racing. Do you find the 1.5 torsen a good balance given the rear bias setup you describe? I've never tried anything else in my car but I can make my Forza video FD do some crazy things under braking with a different lockup.

Railgun

Hahah...Howard, you read my mind. I was starting to fire up an email to you on this very subject.

Thanks for saving me the work , but more importantly, thanks for yet another killer thread!

MaczPayne

iTrader: (5)

I think he meant hot, especially if he had the auto deflators listed in his write-up.

Howard Coleman

iTrader: (6)

hi all,

i have been off the net for a few days due to installing a new computer setup.... vista and all that. i should be back on track, well not on TRACK, if you get my drift..., well not DRIFT

WOW DAYTONA

soon,

hc

maxcooper

Awesome thread howard, thanks for posting. Now I can point people to this thread when they ask me suspension questions, instead of just telling them to search for your posts.

The "weight transfer" discussed in this thread is lateral (side to side), not front to rear. Less weight transfer IN (not "to") the rear improves rear traction, relative to how the car was before you made the change that reduced the rear weight transfer.

-Max

WidefootRacing

iTrader: (3)

Hi Howard,
Wow! Very comprehensive and informative, looking forward to keeping an
eye on this thread. Not to mention, thanks for the "Widefoot" plug!

David Breslau
Widefoot Racing Co.

Smokey The Talon

iTrader: (33)

Max, could you post up your experiences running a squared tire setup (285/30 all around yes?) as opposed to a staggered setup? Did you change your springs or swaybar settings to accomodate?

Socamoto

Nice article!

Does the spring differ at all depending on the amount of anti-roll and tire size?

I have Cusco anti-roll bars front and rear, and I'm just wondering if the 8 - 6 rate would still be a good purchase?...

Thanks

Jon

gracer7-rx7

iTrader: (16)

^keep one other thing in mind with regards to spring rates on a street driven car.

Stiffer equates to less traction in wet weather. When I had the RSR coilovers that howard is running, my wet weather traction worsened enough for me to opt for a softer setup. At the time I lived in an area that got a lot more rain than I do now. These are some of the compromises you need to work through and think about as you think about a combination street/track setup.

justturbo2

iTrader: (4)

great info sticky

Howard Coleman

iTrader: (6)

thanks all for your interest and contributions.

post 20.... i just used the power steering rack and looped the lines. i imagine there are some how to do threads... i made this mod in 99 and it has worked fine since.

post 22... the FC is really different than the FD. the two key differences are the chassis is quite flexible and the McPherson strut front end. these two unfortunately double up against each other. you don't want roll w a strut suspension as they don't deliver the camber gain that a double A arm does... so you run a bunch (3 degrees) of static camber and stiff springs and bars. but when you stiffen up the suspension the chassis flexes. the FC needs a roll cage to deliver adequate rigidity. i will leave the subject to others. in the FC Section.

post 28... no rust on my Teins.

post 29... yes, my spring rate is a bit more than stock in the rear but i run 54% rear weight and wider tires and wheels in the rear. i am finally replacing the OEM bars as i do feel the car needs a bit more roll stiffness. i am going up approx 60% in the front and 36% in the rear. we will see how that works ontrack. the front will have a + and a - setting. i also could switch front bars if necessary. i really like the Tanabe +36% uprate in the rear w the stiffer front. i think that will work out just about right. yes, the shocks are soft in the rear to promote compliance/stick. 30-27 is a good setting to run set cold around the street. 30-27 is a good setting ontrack hot. if you go out at that setting you will come in w higher (probably around +5) and you should bleed the tires back down. the pyrometer will tell you what the tires want.

post 30... i agree w everything. notice the tires are "telling" him what they want. you have to be able to read your tires. a pyrometer is the key. instrumentation removes the need for genius... or luck.

post 39.... yes, the 8/6 would work very well w your bars.

oh, gracer7 is right on the money w re to stiff suspensions in the wet. if you are running the 10/8s and find yourself in lots of rain 'best be very careful as the car isn't going to be talking to you V the 8/6s. too much bar will also be a problem. we raced in the rain and besides bolting on rain tires we disconnected our bars and set the shocks very close to full soft. all in an effort to develop as much feedback as possible. lots of white knuckles. i have a cool incar video from my RX3 from Road Atlanta. i was running third in my first Runoffs and it rained a bit towards the end of the race. i was going 143 mph at the bottom of the hill after the long back straight before going straight up to the bridge and cliff/last turn before the flag. on slicks with the wipers going. everyone in that race has the mindset that you have all winter to rebuild the car. Bruce Short from Palos Verdes was less than 5 feet in front of me and you can hear a harmonic between our two rotary engines that were running almost exactly the same rpm.

hc

frankadelic

I think I learned more about suspension/chassis setup in this thread than anything I have ever read. I also think Howard just saved me a bunch of cash! A few ?'s for you sir:
1)If I change out the front sway bar (OEM) to a Tripoint bar (.188) and the Widefoot mounts are you suggesting that I need to balance that change by also changing the rear swaybar as well? (Based on your comment about decreasing front grip)
2)How is "center of gravity" defined? You quote 17"??
3) What is the correct ride height? How is that affected by rim/tire size.
4)I'm running GAB super R's with the Eibach pro kit springs. How do I determine spring rates (Can only a shop tell me this?) so that I can achieve your recommended 8KG/6KG rate?
5)I recently changed out my trailing arms and toe links. Did I just blow unnecessary cash or screw up my suspension geometry? I can't even remember why I did it....LOL
6)Is it assumed corner weighting is taken into consideration when setting up the car to your specs?

Sorry about all the ?'s just a non engineer/ mechanic trying to understand all this stuff.

Cheers,

Frank

Howard Coleman

iTrader: (6)

Frank,

thanks for your questions.

spring rates.

just to review... stock is 263 front and 195 rear.

Eibach Pro Kit (which i really really like if you run close to standard size wheels and tires and an occasional track day) raises the rate 33% to 350/255. they also lower the car perfectly. remember low is fast.

i run 432 front 378 rear which is 8/6 metric. i bought my coil overs from M2 and they are RSR*s which are rebadged Tein HAs. at time of purchase (1999) there was one rate, 8/6. since they are not the standard racing diameter spring there were no other options. i did find that that rate worked well but might have opted for a 350 rear if offered. if i were to switch coil overs to a standard spring i would go to a pounds per square inch rather than metric as they can be bought in 25 pound increments and are readily available through any short track vendor. ( i used alot of short track suspension stuff on my racecars. i think they are way ahead of most sports car engineering) so if i had my pick i would go with 450/350. the closest to this is what i have at 432/378.

summary: for a dual purpose FD.... either Eibach Pro Kit for near stock sized wheels/tires or a coil over at 8/6 or 450/350.

if you change to a Tripoint/Speedway Engineering bar you do need to change the rear to optimise. you could leave the stock rear bar and eventually balance the car but you would be doing it by compromising front grip. a lose lose. i am checking w Tanabe to see what the rate increase is for their front hollow bar. Evasivemotorsports lists front and rear at $153 each which would be a bargain if they have the correct rate for the front. perhaps the easy bar choice might be the Tanabe front and rears. i should learn the front rate today or tomorrow.

the center of gravity is determined by tipping an object to the point it falls over on it's side, extending a vertical line from the edge of the base straight up thru the object. do this on both sides. the point of intersection is the center of gravity.

the lower the CG, the less lateral weight transfer.

as to "correct" ride height... i don't know, but have found that 25 inches at the top of all four wheel wells works nicely. any lower and you run into bump stop problems and will be unable to dial enough camber gain out of the static setting to drive rationally on the street. (unless you make adj upper A arms...)

if you read my thoughts on bushings... you did the correct thing w the lower links and you didn't hurt yourself on the toe links. just make sure to re-align your car to my specs...

corner weighting, or "scaling" your car is generally way down the to do list on a priority basis. i favor setting the car at 25 inches, moving whatever weight you can rearward, downward and to the passenger side. at that point you have what you have and i wouldn't jack the ride height around.

hc

2MCHPWR

iTrader: (2)

hi andy - congrats again on doing so well at the SCCA nationals! another trophy for you
can you tell us exactly what swaybars you use? i think you use the tripoint one. is that the normal one they sell? what thickness bar? i have 1.88 on order with them.
oh and what brakes do you use, and what is your ride height? thanks man!

Rotary_Rocket!

iTrader: (2)

Howard,

With all due respect I’ll have to agree with others here that you seem to have missed the mark on a couple of key issues.

A) As others have mentioned, one of the first issues to address if your giving advice on RX-7 suspension is to manage (stay off of) the bump stops.

B) You should defiantly have a closer look at your toe links. While there are indeed solid bushings on both sides, one side is completely encased in rubber and will allow significant movement under stress. To advise a “0” toe setting with the stock toe link is certain to result in a toe out condition under braking and during turn in. Not good. I am surprised that even the experts who you had look at the suspension didn’t pick up on that.

C) Are you sure you got your RSR coilovers from M2? I don’t recall them ever offering or even liking them and do remember this article where they actually removed them from a project car.

There is actually a lot of info in this article on the subject:

http://www.sportcompactcarweb.com/pr...t_7/index.html

I think the writer misspoke however when he said they ran a softer front spring. I believe they used a 550/450 setup in their basic kits and mine are even stiffer. Otherwise my car had the same setup as the one in the article and it drove like a dream both on and off the track. I believe my street car did a 1:40 flat at Laguna several years ago with this setup and was perfectly comfortable on the ride home. I can’t even begin to tell you how much better the braking is with the stiffer springs as well as the car stays very flat under braking allowing for the rears to actually do some work. With all of the effort you have into improving your rear brakes, you may want to consider this point as well.

D) You seem to put a lot of emphasis on static weight percentages and scale readings in relation to spring rates which is a bit misleading. As soon as other forces come into play that all goes out the window and changes according to spring rates, right? I can usually get a pretty good balance in my hammock as well until I have to reach over for my drink!

Cheers

Larry

Howard Coleman

iTrader: (6)

larry,

bump stops

i don't recall driving a stock suspensioned FD. my wife has Eibach Pro Kit springs along with rod-end longitudinal lower links, solid aftermarket toe links along w 18 inch tires. she actually drives faster on the street than i do most of the time. she is very sensitive to setup and has never complained about hitting the bumpstops. Eibachs take the car down into the 25-26 inch rideheight region. i have driven her car a fair amount and have never noticed it hitting the bumpstops. my car has no bumpstops and does exhibit the proper max amount of suspension travel. maybe you are referring to stock FDs.

you are probably correct on the rear toe links and i appreciate you making the point. there is no place for a rubber bushing on this very important link. since it, like the lower longitudinal link, does not carry vehicle weight it isn't a big deal re NVH.

yes, i am certain they are RSR's. i still have the RSR specsheet that arrived in the box. they really are just a rebadge as Tein HA is stamped on the shock body. RSR decided to not offer them shortly after M2 introduced them in the Sport Compact series ( which i still retain in my files) so M2 "decided" that they weren't up to snuff and headed in another direction.

yes i do emphasize static weight. i also emphasize dynamic weight. both are important. static weight flows through the various paths such as roll centers and ends up as dynamic weight. changing static weight changes dynamic weight.

hc

jantore

I must agree with howard on alot here. Im what u would call an amature on setting up race cars. But have learnd a few leasons during the last 4 years.

My setup is as follows

Tein RE coilovers 16/16kg spring rate
Running them at 8 clicks in the rear and 4 in the front atm
Racing beat swaybars front and rear.
Rotor Extreme Toe Links and trailing arms.
Kaaz diff sett to 33% locking, will try 66% this summer.

The ride hight is alittle higher in the rear then in the front. Not sure what it, actually is. Camber is about -1.7 up front and about -1.2 in the rear. Toe in is 0 in the rear and got about 1/16 toe out in the front.

Im running Yokohama A048R 285/30-18 on 11" rims in the rear and 265/35-18 with 9" rims in the front. Tire pressure cold is about 25 psi

Have not been able to test temprature on the tires since ive been mostly alone when racing the car.

The car is stable, feels verry good to drive, and got increadble rear end grip. But the car is pushing the front trough the corners, and i have alot of understeer if i try to take the corner faster.

Now the thing im doing with the car this winter to improve the front grip is. Removing some rear weight. About 10kg, since the car is about 70kg heavier in the rear.

I will add a front splitter to the front bumber and carbon canards to pull the front more down. Im also adjusting the breaking balance, as we have spoke about before howard, im still running stock rear breaks and the stock break bias in the rear.

Once i get this done, i will take the car to the track. And i got a freind of mine that used to race alot a few years ago to go with me. And we will check tire temps and tire preasure, to see if we need to change preasure and camber. I have already booked an entire day for testing in may.

Now to give u an idea of the car, it has the GT300 02 Wide Body kit from RE-A with the RE-A GT II wing and carbon diffuser. Estimated power this summer will be about 600hp at the flywheel. The car is a race only car.

So howard do u have any suggestion to some things i should do to my setup?

Regards
Jan-Tore

Howard Coleman

iTrader: (6)

hi Jan,

nice to see you on the thread....

your car should be loose. real loose w the 16KG springs in the rear. your push comes either from AERO or it is because you are on the other side of Greenwich Mean Time.

please tell me that you were running that wing (in your picture) while all this pushing was going on.

AERO is HUGE above 55 mph and goes up at a cube rate. it doesn't take much to upset the delicate longitudinal balance.

AERO STORY:
Runoffs at Road Atlanta. my RX3SP gridded 4th after the first of two qualifying sessions. i asked my engine guy Daryl Drummond what he would think about removing the tiny little rear (OEM) spoiler pop riveted on my rear deck. Daryl asked me what rpm in top gear i was running at the bottom of the hill. i said 10,000. he figured i'd pick up another 300 rpm. the engine was drysumped and running 12 quarts of oil. Daryl figured it would be 50/50 the motor would live as it was already cranking big time down the long back straight. since we had another engine in the truck we removed the rear spoiler.

the spoiler didn't weigh more than 2 pounds!

out i went and did run 10,300 at the bottom of the hill BUT i could not hold the car at the very very slight, almost imperceptible bend leading to the hill. the tiny spoiler at about 140 was glueing the back end to the track.

on the other side of the track, down and up the hill thru the esses, the car was major loose and this was all 3rd gear!

after the session we pop riveted the spoiler back on.

it was tiny. it was out of the major air stream and it was essential.

i have huge respect for aero. that does not mean i am for spoilers. it is really easy to add too much drag or unbalance the car. i run the R1 splitter and no spoiler. the car is perfect in turn one at Brainerd at 165.

since you will have around 500 rwhp you probably have enough excess rwhp to use Aero.

i suggest you lose the 16KG rear springs and substitute 13 or 14. start at 2 pounds lower air pressure in the rear. then tune your aero. and do bring a pyrometer to the track.

good luck,

howard

AMRX7

Thanks, rain was not my friend this year but that's the way it goes sometimes.

I have a custom blade adjustable bar in front 1.25"diam. Not sure on wall thickness as the ends are welded to blades and it would require drilling to find out (came with the car when I bought it). Rear I ran the RB 19mm hollow bar, but have gone to a stock rear bar. To put power down more effectively, I try to minimize rear bar as much as possible, though you need to compensate with spring rate increases. At some point I'd like to get to where I use no rear bar.

I use stock brakes with Carbotech Panther+ pads. Can't say enough good things about those pads for autox.

Ride height is a little trickier to reference since I no longer have any stock fenders. Measuring to the frame rail at about the front jacking point, I have a bit under 5" to the ground. That is my lowest corner due to running some rake, and corner weighting effects. I'd like to go lower, but I can't touch the chassis and my height is dictated by the tires just missing hitting the top of the fender at full bump. I do have roll center correction in the front, but haven't gone too radical with that yet.

-Andy