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Old 01-22-08, 11:16 PM
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howard coleman's FD Chassis/Setup

As I was answering yet another PM (probably 5/week) regarding FD suspension and setup it finally occurred to me that I could do a win-win deal…

Win… I don’t have to wear out my keyboard repeating myself.

Win… hopefully more people could benefit from my help.

While I am not Mario or Craig Carter I have spent the better part of my life very seriously trying to win road races. 22 SCCA seasons, the last 6 in a GT3 Mazda RX3. If that sounds like old school stuff, and it was being back in the 80s, consider this:

The laws of physics haven’t changed in the last 15 years.

My car was a tube frame purpose designed and built plastic bodied RX3.
Some of the features (many legal) were:

Driver adjustable (as in during the race) ride height. You burn 65 pounds of gas, you’d best crank a ˝ inch into the right rear to rebalance the car.

Driver (cockpit) adjustable blade type front sway bar

Tire pressure bleeders. Instead of doing the first lap at 25 psi when the tires like 29 when hot you start at 29 and as they gain pressure the valve releases it.

Very secret sauce on my tires.

The combo of pressure reliefs and painted tires allowed me to go as fast as I could into turn one lap one. While everyone else was on underinflated cold tires.

Speedway Engineering Quick Change rear end. I was the first to run it in GT3 now it is standard issue. (it was supposed to soak up too much HP. No.)

Wide 5 magnesium hubs and wheels… (check them out)

Dry sump Daryl Drummond motors. Hp band 7000 to 10,000 the entire race.

1.5 degrees negative camber with a solid axle. Now how did I do that.

72 SCCA National GT3 races in the ultra competitive CENDIV. 27 wins. A second, two thirds and two fourths at the Runoffs at Road Atlanta. Two June Sprints wins at Road America. Lap records at Road American, Brainerd International Raceway, Blackhawk Farms, Mid Ohio, Indianapolis Raceway Park.

car in year one form, modified from IMSA RS format by Roger Mandeville, first Nat win at Blackhawk


six seasons later nothing left but the windshield and roof, over 10 seconds a lap faster at Road America





I don’t consider myself anything special, I just wanted to race. Given the same situation you probably could have accomplished something similar. The reason I bring this all up is to give you a frame of reference as to the following advice.

Before I get into it one more caveat… there are lots of ways to skin the cat.
This is what works for me.

The FD is a magnificent roadcourse car. My friend bought his off the floor of the Minneapolis Auto Show and after driving it a bit made the mistake of asking me, “what do I do to keep the rear end from sliding around?”

I told him there were a number of options. He could bleed 3 or 4 pounds of air out of the back tires or spend a couple of hundred thousand $.

We settled in the middle and off the car went to my absolute favorite chassis guy and good friend Craig Carter. Craig did an entire suspension plot of the car.

He called me and was incredulous describing how the whole thing was pure race suspension geometry. This is from Craig Carter who told Jack Roush’s TransAm crew that his mustang needed a quarter degree more camber in the left rear. We were ready to move suspension pickup points and didn’t have to touch them.

With modest chassis mods Frank and I ran 4 Ferrari Club of North America events at flat out Brainerd Int’l over a few years. There were all kinds of cars… Ferrari Cup cars, Vipers, Corvettes, Porsches you name it. I was never beaten and I never saw anyone pass Frank.

Quick Frank story… Frank looped his FD in turn one. Turn one is after a 6000 foot straight and is a banked, wide radius 90 degree (think Daytona) turn. I honestly believe that might have been the fastest FD 360 ever. Approx 150+ mph. We considered renting a helicopter to hover over turn one and take some pictures of the tire marks.

Quick Ferrari story… Frank and I around the Friday night dinner table listening to featured speaker and former Formula one driver Derek Bell… a guy across the table was talking about his Ferrari with us. The next day he happened to be in the pitstall next to us and was in and out and not happy with his car. Noticing his consternation I asked him what was going on. He said that his car was a piece of garbage in the turns. I immediately asked him what tire pressure he was running.

He said that he’d just bought a new set of tires and the guy told him explicitly to run 40 psi.

I grabbed my tire gauge without further word and aired his tires down to 29/26. you’d have thought he won the lottery. He ran thru two tanks of gas during the day and was having a ball.

Oh does the right tire pressure matter.

Back to the FD.
So the FD is a super car. It can be made super better. It can also be screwed up. Let’s make it super better.

First let’s start at square one. The FD is a front engine rear drive car. As such, the primary challenge will be to promote rear traction. When you get things dialed you will be focusing on the back end. Think of road racing as drag racing from corner to corner. Consider two cars both able to run identical quarter miles. If one car gets a 1 second head start it will win the drag race.

If you can put your right foot down earlier coming out of a corner than your competitor you will be looking at the next corner first.

Driving fast and being able to get the most out of your car is about feeling comfortable. Being comfortable is about your car telling you what it is about to do in advance. Properly set up your car will talk to you. A properly dialed racecar will give you advance notice so you will find it easy to drive at the limit.

The opposite is… “it just snapped on me.” Spoken typically by someone who has just had an offtrack excursion.

To go fast you need to trust your car.

Which brings me to subject one… lateral weight transfer. Ideally you want equal weight on your lateral tires. Too much weight causes the tire eventually to wash out, lose traction. Further, every pound transferred to the outside tire is removed from the inside tire diminishing it’s value.

There is a major point of confusion here that needs to be cleared up so you can get tuning.

There are only two items that determine total lateral weight transfer…

Center of gravity

Track width.

The typical FD weighs 2900. add 200 for the driver… 3100 pounds. Remove the unsprung weight (wheels/tires, brakes, half of the A arms, half of the shocks/springs, half of the swaybar, half of the driveshafts). Call it 350 pounds.

So… 3100 minus 350= 2750 X 15.5 (center of gravity for stock FD is 17 inches, our track car is lowered a bit) X 1.1 G’s divided by the track (stock is 57.5 minus your positive offset wheels so we use 55.5) = total lateral weight transfer in a 1.1 G turn.

That’s 844 pounds of total lateral weight transfer.

So what can you do about it? Given the ride height and track… Nothing.

But if you put stiffer springs and roll bars on the car it won’t roll as much. Do you see roll anywhere in the aforementioned equation? You can weld the suspension solid, you can bolt on 2000 psi springs and a 6 inch swaybar.

And you will still transfer 844 pounds.

But springs and roll bar stiffness can apportion (front to rear) where the 844 pounds transfer. By changing the longitudinal roll stiffness you can move more of the 844 pounds to the front or to the rear.

And that is one of the ways we can trim our chassis… understeer, oversteer. If, for instance, the chassis is balanced and we increase the rate in the rear we will transfer more of the 844 rearwards and will tend towards oversteer.

BTW, a common mistake when attempting to longitudinally balance a chassis is to work on the wrong end. Let’s say the car is oversteering (rear loose). You could stiffen the front by adding spring or bar but you would be decreasing front grip so it would balance against poor rear grip. You just lost total grip.

The correct path would be to find a way to increase rear grip.

Stiffer springs and shocks do decrease body roll and that is generally a good thing to a point. The FD, due to it’s double A arm front and rear suspension and attendant negative camber gain on bump, is not as effected by roll as most other cars. That is as the crucial outside wheel in a turn moves up into the fenderwell w body roll the suspension adds negative camber thus keeping the wheel properly cambered to the track.

That’s why the FD takes few prisoners ontrack.

Some cars need to run huge springs and bars to kill roll because their suspspension goes off camber in bump. These cars with too much spring rate are very hard to drive near the adhesion limit.

The stock FD spring rate is 263 pounds per inch in front and 195 pounds in the rear. These are my numbers from my Longacre Digital Spring Checker. Just FYI, with linear rated springs the rate increases with contraction. The second inch of the FD front spring is 526 and the third is 789…

I run 432 front and 378 rear. Expressed metrically 8 KG and 6 KG. I am delighted with this rate. If my springs vaporized I would repurchase this rate. It works on the track. It works on the street.

That said, Frank runs 566/422 or 10Kg/8Kg. I consider this rate the outer limit.

Remember, both rates transfer the same lateral load. The higher the rate the harder it is to drive at the limit.

Let’s talk spring and shock options….

Interestingly, the suspension area is one where more money does not necessarily buy more speed. Although there are plenty of vendors wanting to sell you high dollar stuff…

You have two options.

Replace the OEM springs and shocks with aftermarket.

Replace the Oem springs and shocks w a unitized component known as a coil over.

Both work very very well if you select the right stuff.

While there are a number of options I have been extremely happy with the Eibach Pro Kit springset. The rate is 350/255 and they lower the car close to the proper ride height. At a price of around $200 and often seen in our classifieds these extremely high quality springs TRANSFORM the FD. Do not discount this easy to install option.

I owned a Shock Dyno for a number of years. I dynoed 31 OEM FD shocks. They varied between 3500 and 135,000 miles. Interestingly they all dynoed similarly. I like them with the Eibachs.

There are various other aftermarket shocks that would bolt in but I suggest you just try the springs. You will be surprised.

The Coil Over market is sort of like oil. I have always used, and have been sponsored by Mobil One. It has worked for me. Could I really tell you why it is better than XXX? Nope. But if you start a thread on oil you will have many posts on the subject. Ditto Coil Overs. Double adjustable, digressive blah blah blah.

The first question to ask re coil overs is WHAT IS THE SPRING RATE. If you want to slide around buy something with a rate over 10Kg. Or pump up your tires to 75 psi, it’s the same thing.

It is really easy to get into overkill on coil overs. If that’s your deal fine. For the other 95% including me I will be very happy with my modestly priced Tein Has. The valving, remember I have a shock dyno, with 16 settings will give you everything from loosey goosey to rock hard.

My view is after you have spent a few years on the track and have a handle on things and you have nothing better to do you might consider something up the food chain.

There is a lot to learn in the basics area before you get to esoteric. Admittedly that just my opinion here.

Then there’s the “pillowball” upper coil over mount issue. In a word, don’t.

The upper mount of the OEM spring is a rubber insulator. This insulator helps absorb lots of unwanted vibration. There is not one bonafide engineering reason to change the upper mount to steel. Yes, “pillowball” equals steel.

Here’s the key… the upper mount has NOTHING to do with the suspension geometry. There is NO performance advantage. The A arms scribe the geometry. If you do coil overs retain the upper rubber mount.

Swaybars are always an excellent way to control roll and tune for over/understeer. The additional roll stiffness a properly selected swaybar provides allows the springs to be a bit softer thus allowing the tires to spend more time where they belong contacting the pavement.

I am in the late stages of changing my swaybars from OEM. I am installing a Speedway Engineering hollow front bar (35 inches X 1.25 O D X .188 wall thickness). I bought Speedway’s collars and mounting brackets and will purchase their aluminum arms. This will add approximately 60% more roll stiffness than the OEM bar. It will have 3 fine tuning adjustments. I will bend the arms, drill the holes and fab the links.

Mazda went a little crazy lightening the front swaybar mount. Lots of swiss cheese lightening holes… it is probably fine with the stock bar but when you upgrade to a stiffer bar you MUST lose the mount. I strongly suggest you contact Widefoot and purchase their swaybar mount.

I spent some time looking at rear bars. Remember it is important to keep the rear a bit soft to provide traction. (I run my front shocks 7 clicks from full soft and my rear 2 clicks from full soft). After doing my homework I decided to go with the Tanabe 20 MM hollow rear bar. It is up 36% from my 93 bar. I haven’t been ontrack with either but think they will work well considering my spring rate is up a bit over 60%.

Continuing talking hardware… There are lots of bushings in the FD. Most of them should be just left alone. I would not change any bushings in the front. In the rear there are two sets of bushings that should be changed.

The lower longitudinal link that absorbs all the braking and acceleration has a big fat rubber bushing in the front. It needs to be replaced. I really like the beautiful aluminum OEM suspension members and consequently removed the bushing and substituted a nylon item. It is also easy just to replace the link with an aftermarket item that employs a spherical bushing. If you don’t replace this bushing your wheels will be toeing in and out on acceleration and braking.

The other set of bushings are the two at the top of the differential. If you place a jack under the diff you will find it moves up almost an inch before the car starts rising. A big no no. lots of driveline chatter. Nylon works for me.

I believe there may be a higher durometer (stiffer) bushing available from Mazda. That would work.

some replace the rear toe links. while there may be a miniscule amount of non metal in the spherical bearings they look solid to me so i am fine with stock.

Tires of course are a key. I suggest running tires that offer a tread width equal to your rim width. I run Enkei NTO3+M wheels. 18 X 9.5 front and 18 X10.5 rear. 255s front, 295s rear.

We certainly will be offered more tire options this year as the market is changing rapidly. Lots of options in the stickier 100-200 UTQG category.

That’s about it for the hardware let’s move on to setup and tuning.

Chassis setup is HUGE. You just have to get interested in it if you care about going fast and having fun at the track. I will give you a nice dual purpose setup and once you get to the track if you want to go fast you will be changing some of the settings.

Alignment of the FD is an easy task for a shop so don’t let them give you a big song and dance about it. Tell them you want the car set to these specs. Period. Further, arrange from the getgo to get a complete printout of the before and after.

Tire pressure 30 front 27 rear
Ride height if you have coil overs should be set at 25 inches at the top of each wheelwell.

Toe in front between a 1/16 and 1/8th inch
Toe in rear zero
Camber front and rear 1.2 degrees negative
Caster equal minimal
Zero rear thrust angle.

Prior to going to the track I suggest you place a tie wrap on each shock absorber piston rod and push each wrap down just before going out. When you come in they will tell you how much travel you are getting.

For one inch of bump at the wheel the shock moves .6 of an inch in the front and .68 in the rear. You are looking for no more roll at the wheel than about two inches.

I recommend if you plan to track your car that you purchase an accurate tire pressure gauge with a bleed valve and a pyrometer. You are almost blind at the track without a pyrometer. Good digital pyrometers can be bought for approx $150 and are essential.


Set your air pressure and run 3-4 laps. Pit, check your tire temps immediately, and your pressures after… record all 3 temperatures from each tire. You want 20 degrees more temperature on the inside third of each tire. If you don’t have it you need to adjust your camber. I do it at the track in a few minutes.

The pyrometer will tell you the correct tire pressure for each corner of the car. All will be different.

That’s about it for now. I hope this will be of help. It has worked for me.

howard coleman

Last edited by Howard Coleman CPR; 06-27-15 at 10:47 AM.
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Old 01-23-08, 12:58 AM
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Howard,

super post. I wish I had this info when I started the crazy upgrade path on my suspension.

Bob
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Old 01-23-08, 03:11 AM
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very nice post howard, I feel like I just went to school...great info...
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Old 01-23-08, 08:04 AM
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God damn, coles notes!
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Old 01-23-08, 10:06 AM
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sticky!!
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Old 01-23-08, 10:19 AM
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Hey Howard, do I need to run more camber if i use r comps? I also have people on the contrary telling me to run as much caster as possible. What effect does caster have on the handling?
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Old 01-23-08, 10:36 AM
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Howard, did you ever get surface rust on your Tein HAs?
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Old 01-23-08, 11:13 AM
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Howard,
I'm curious about your thoughts on spring rate relative to stickier tires. The amount of roll you'll get with a stock or larger street tires is not the same as what you'll get with a 285 Hoosier. At 500/400 w/ hoosiers, I can get the wheels to rub the liners on hard corners, with a 25.25" ride height. I'm thinking in terms of 600/500 as an upgrade.
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Old 01-23-08, 12:45 PM
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Great thread! Archive this!
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Old 01-23-08, 01:23 PM
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caster:
caster in larger amounts is bad. it is used as a band aid in many front wheel drive cars in attempt to fight torque steer. here's a fun thing to do. in most any front wheel drive car turn the steering wheel lock to lock and "watch what happens." you will note that the large amount of caster raises one corner of the car at full lock and drops the other front corner. this transfers weight. not good. stay w a modest amount of equal caster.

camber:
properly set camber on track seperates the men from the boys. if you are going to put your car on the track either borrow or buy ($150 buys a good one) a pyrometer. set your car as i suggest and then hit the tires w the pyrometer immediately as you return from doing 3-4 laps. the readings will tell you exactly how much camber you need at each corner and also exactly the correct tire pressure to run hot. you will find camber and pressure should be different at each corner.

spring rates and stickier tires.
as you generate more lateral Gs you do transfer more weight. for instance, using the above formula and changing it to 1.3 Gs... 2750 X 15.5 X 1.3/55.5= 998 pounds of total lateral weight transfer. this force works thru the center of gravity and roll center and results in more body roll. i favor going up on the swaybars rather than springs. the springs primary job is to keep the tires in maximum contact with the track. the swaybars job is to control roll.

what are you running for swaybars currently?

hc
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Old 01-23-08, 01:54 PM
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They are PFS tubular sway bars, which I remember being quoted as "60% stiffer than stock" in the PFS literature, with urathane bushings and Widefoot mounts. The rear bar has a two-hole adjustment that I've always left in the softer of the two positions.



Originally Posted by howard coleman View Post

spring rates and stickier tires.
as you generate more lateral Gs you do transfer more weight. for instance, using the above formula and changing it to 1.3 Gs... 2750 X 15.5 X 1.3/55.5= 998 pounds of total lateral weight transfer. this force works thru the center of gravity and roll center and results in more body roll. i favor going up on the swaybars rather than springs. the springs primary job is to keep the tires in maximum contact with the track. the swaybars job is to control roll.

what are you running for swaybars currently?

hc
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Old 01-23-08, 02:05 PM
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Howard,
Your writeup is great. It did make me curious about the difference in spring rates between the competitive auto-x FD's opposed to an open track car.
I understand that most of the national champion auto-x FD cars (ASP, SM2) have run huge spring rates in the front of the car (750 lb. plus) is this due to higher braking loads in auto-x when compared to roadracing? Any thoughts on this?
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Old 01-23-08, 02:19 PM
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Howard, great read. I beleive you just laid out exactly what I will buy for my suspension. Would anything in your post change significantly if say I ran 285's front and 345's rear with a wide-body kit?
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Old 01-23-08, 02:24 PM
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Excellent post. This has been a good week for the forum, between you, Rich, Damian and others, there is some great info popping up on this site
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Old 01-23-08, 03:02 PM
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Minimal caster means minimal differences left and right right? How about the angle? Also, Is there a way to tell if the springs are too soft or stiff for a cars current setup?
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Old 01-23-08, 03:05 PM
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Very informative! Thank you!
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Old 01-23-08, 03:36 PM
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Excellent thread. Thanks for sharing.

If I may provide input regarding Caster, I'd suggest 6 degrees.

I've played around with different Caster settings on my car last year. I started out near 7 degrees (previous owner's setup) and the steering felt a bit slow. Changed it to 6 degrees and it really livened it up. As it got get closer to 5 degrees the car wants to tram line a bit more and is a bit too lively for my preference (mostly a street car).

Fwiw, my 123k mile shocks were much slower to respond to bumps and dips than a lower mileage set I replaced them with. I later went to Konis all around and the reaction time to road surface irregularities increased just a little bit more.
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Old 01-23-08, 04:05 PM
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Peter... regardless of whether the PFS bar is +60% or whatever you need more roll stiffness. i have seen alot of incorrect estimates for sway bars. many are calculated without actually knowing the wall thickness. i suggest you either contact Tripoint or Speedway Engineering. i am doing the .188 wall front bar and that might work for you. if you later find you need more front roll stiffness it would be a simple matter (30 minutes) to swap in the .25 inch wall bar and resell the
.188 to anyone on the board.

re Autocross... i am glad swilson brought it up. my experience is only road racing. autocross is significantly different and i believe that response may trump other factors so it doesn't surprise me that autocrossers run lots more roll stiffness.

as to caster... the minimal refers to the actual amount, as in 5 degrees for instance. do keep it laterally equal for road racing.

finally just a quick comment on another aspect of chassis setup... static weight distribution. executive summary: you want as much as possible on the back to aid traction.... remember the hooking up the rear theme. i run approx 54% rear weight.

and one of my favorite items to remove from the front is power steering. it has no business on a 2900 pound rear drive sportscar. i ditched it in 1999 and it is still my favorite mod. hello road feel. with power steering you might as well be playing a video game. the wheel is numb. do not remove the PS belt and go for a drive to check it out. you will not be able to turn the wheel. you need to remove the pump and most of the fluid from the rack. an afternoon job with handtools.

taking front weight off the car is addictive

hc
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Old 01-23-08, 04:16 PM
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This is the GOOD DEAL!
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Old 01-23-08, 06:08 PM
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Originally Posted by howard coleman View Post
and one of my favorite items to remove from the front is power steering. it has no business on a 2900 pound rear drive sportscar. i ditched it in 1999 and it is still my favorite mod. hello road feel. with power steering you might as well be playing a video game. the wheel is numb. do not remove the PS belt and go for a drive to check it out. you will not be able to turn the wheel. you need to remove the pump and most of the fluid from the rack. an afternoon job with handtools.
Ah, I've been wondering about this. I figure if you're comfortable using a power rack without the hydraulics attached, then I personally don't feel the need to spend the extra to get a fully manual rack.

Do you simply plumb the two PS lines into each other and leave mostly air in the rack&pinion?

Dave
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Old 01-23-08, 06:33 PM
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amazing post / thread.
makes me kind of sad I have an FC and not an FD

you are a nice dude to share so much valuable info and in such a straightforward manner.

wicked stuff. A+ !!!
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Old 01-23-08, 09:54 PM
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Great read! What kind of info can you share for suspensions like the ones in the 2nd gen?

Subscribed.
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Old 01-23-08, 11:05 PM
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Old 01-24-08, 12:59 AM
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A) Step one is to eliminate the bump stops, especially if you are still using stock shocks and those ***** spring rates. The snap oversteer that took his friend out was likely cause by the bump stops.

B) The toe links do indeed have a significant amount of rubber encapsulating the pillow ball on one end. By running 0 toe in the rear with stock links you are certainlty going to see some highly undesireable toe out under load at turn in, again helping to put your friend through the spin cycle.

C) the rear sway bar does not work well as a substitiute for the ***** spring rates.

D) BTW, my friend who helped set up my multi championship winning FD used to help Dennis Golden on his National and Nasport Championship GT3 RX3, small world huh?

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Old 01-24-08, 07:56 AM
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I know of a few people who are VERY fast on long tracks that use/used high spring rates (800+) and were very pleased with car control and dynamics. There are many ways to skin a cat. Excellent post for those just starting out.
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