fc's have a macpherson strut front suspension and as such the actual rate at the wheel is the same as the actual rate of the spring.

very very different than the fd where the spring sits in the middle of a lever arm (the lower A arm). this position changes the spring rate at the wheel ( referred to as the "wheel rate") versus the actual rate of the spring greatly.

it would be a great mistake to equate any comments as to fd spring rates to the fd.

being a strut (macpherson) suspension the dynamics and therefore the setup of the fc are quite different.

this doesn't mean the car can't be setup to go fast... just not as fast. lots of fcs have run well in SCCA's IT class. talk to those running IT to find out who makes the good stuff. last time i looked it was Carrera.

howard coleman

 

Howard,
Wondering if you would be able to tell me the spring rate of the TEIN HT's. I like the fact that the compression and rebound are independent. Wondering if you could get me some good information/advice on these.
Thank you very much in advance,

Craig

http://www.tein.com/htdamp.html

From the looks of it, they look like they are over 1100lbs??? Not sure if that is right or if I'm even reading it right, but I would sure appreciate you looking into it.

 

http://www.silverbulletrx7.com/coilovers/coilovers.html also compares coilovers.

Howard...I'm also interested to know your point of view on the Zeal B6 and S6 coilovers.

 

Howard
It looks like you got more than u bargained for lol

 

Careful that what you see doesn't deceive you. Look closely next time and you'll see that the cars do roll, but mostly in only one direction. They have a lot of rolll stiffness but it's only in one direction. Since NASCAR stockers make only left hand turns their wheel rates and roll stiffness are set to be stiff in left turns and softer in right turns. Watch them on tv and you'll see they mostly roll only to the left. Often the front swaybar is attached in such a way as to only react in left hand turns, in right hand turns it does nothing. They accomplish this by attaching one end of the bar with a chain or cable so it can only react in tension and not compression too.

There are several reasons for them to set a car up like this. What right turns they do make are just through traffic or to catch the car when the rear goes away. The car intentionally turns right poorly because if the rear were to start coming around a lot of right turn roll stiffness would tend to throw the car head on into the wall when trying to catch it. The other reason the swaybar is effectively one way is that on the banked tracks the right front is the tire that carries all the load, the left front does little in the turn. If the left front were to come low off the banking or run right on the apron it would instantly tranfer load across the swaybar onto the already saturated right front and the car would instantly push. The purposely set the car up so if the left front encounters bumps etc it will not transfer that increased load across the bar and to the right front. This means they do roll but mostly only when turning hard right.

 

I agree about the solid top mounts. Not necessary with the type of suspension the FD has. They're nice on a Mcpherson Strut though. I adapted my Advance Design coilovers to use the stock top mounts so that they're much more streetable. https://www.rx7club.com/3rd-generation-specific-1993-2002-16/hybrid-advanced-design-coilovers-pics-400080/

It was metioned that a lot of folks are running stock shocks or Koni Yellows with high spring rates. Does this really work well? Don't you need to carefully tune your shock to work with a higher spring rate? Shouldn't you get your shocks valved to match your springs for optimal performance?

 

Unfortunately, most purpose-built coilover shocks come with pillowball plates on the top, like the JICs. Other than adding a neoprene or rubber spacer or two between the plate of the shock and the body of the car, what can you do?

I've also heard that the JICs aren't that harsh on the street, despite the high spring rates. Is it really worth it to replace the springs to get closer to 560/450? 670/500 isn't that far off, especially in the rear.

 

My Koni Sport coilovers were valved by the local Koni technician before he left Tripoint, but the units have adjustable rebound damping anyway. The overall ride is better than stock (and I include "smoother" in that definition), even with the heavier rate springs.

 

there's the usual tradeoffs between single and twin tube shocks...

single tube allows for a larger piston area which allows for more sensitivity.
OTOH, if the outer casing of a single tube shock gets dinged it is history.
cost differential does not relate to single/double but valve type and materials.

i am not opposed to single tube shocks. if i were racing a formula car at around 1400 pounds maybe i would be able to find a difference...

but a 2800 pound fd w mostly rubber-bushed suspension? the differential would be so far down the list of priorities. it is much more important to have the correct spring rate/ within 25 pounds of optimum.

as i said, i have a shock dyno and shocks are pretty simple things. they have 3 sets of valves... high speed for bumps, low speed for corners etc. their primary function is to control spring oscillations... do too much overcontrolling the spring w shock settings and you screw up the spring dynamics.

i have dynoed over 30 OEM fd shocks. regardless of miles all but one (hydraulic leak) spec'd out perfectly. the OEM shocks work great w aftermarket springs up to 350 pounds. beyond that you should go to aftermarket shocks.

shocks are not as important as spring rates as most shocks can be dialed in to the area of the spring requirement. i am not saying shocks are unimportant, just nowhere near as important as spring rate.

on the subject of springs... we all know they are really progressive don't we?

in other words, a 500 pound spring moves one inch w 500 pounds on top of it. it takes 1000 pounds to move it the second inch and 1500 pounds to 3 inches! a 900 pound spring takes 1800 pounds to move it two inches, 2700 pounds for 3 inches!

the above are progressive but in a linear fashion. "progressive" springs move upwards in a non-linear fashion... 500 for the first inch and, say 1200, for 2 inches...

you can see that running a 700 pound static cornerweight fd will encounter almost no compliance as it goes into bump very quickly.

successful performance engineering is about priorities... get spring rates right.

howard coleman

 

How about the Cusco Zero 2s. I called up Nukabe and they said they have a 10k front and 8K rear spring rate. How do you think these would be?

 

Endless told me that the pillowball on top just wear out faster and transmit more sound. They said that pillowball mounts are not needed for applications such as ours and thus their coilovers do not come with them as a standard. (They are optional.) This is for the FD. The FC might come with them due to the differences in design.

 

On my CRX, my KYB AGX's can not handle the spring rate of my Nuespeed/H&R's and the ride quality sucks. The Tokico's handled them well but an x-g/f went off road and blew them. The pillow ball/upper mount would have possible saved my hood as the damper allmost went through it.

On my RX7 I have JIC-SF1's. The spring rate is 10kg/8kg. Slightly bumpy but for the excellent handling it's a good trade off. I think it's would be a perfect track rate and personaly would prefer 8kg/6kg for street as recomended for the FC. Oh, the FC has the adjustable upper mount because they can't be adjusted through the links like ours (something like that). The SF1's are double piston and you can hear them whoosh on every compression.

 

just a quick math review on coil overs.... i always think of springs in pounds/inch and many of the vendors express the rate in KG/mm.

just take the KGs, X 2.2 X 25.4 and you will have pounds per inch... real easy.

so a 10/8 spring set would be 558/447 right at the edge of o k for street and track.

a 8/6 would be 447/335..... that's what i run and really like.

howard coleman

 

That's interesting. I've never seen the JICs with anything but the pillow mounts. I wonder if there's something that could be adapted or if they have a bushing-style upper mount available.

 

My thoughts exactly.

Anyhow, I wish I knew more about them before my purchase. I would have bought Bilsteins/eibachs for less since I was on a budget but more likely I would have looked for Sustec Pro's on sale and if not on sale I would have got Buddy Clubs. Well actually, they've come down in price since they have a US office now. Rotaryextreme can get them in 10kg/8kg which is nice for an adjustable setup. I had previously spoken with both Buddy Club and HKS about having the same spring rate (I'd imagine the same for Apexi) and was told that the front and rears are valved differently and they prefer that method over different spring rates.

 

Howard (or anyone for that matter, i'm just saying Howard because his post kicked ***)-
Have you had any expierence with/know anyone with expierence with spherical bearings in the suspension? I was checking out Sport Compact Car's (yes, i know they like honda, but...) project cars, and in their last installment of their project 300ZX TT, they put speherical bearings in the suspension, and they said it took away any and all wheel hop, along with making their ride smoother by removing the binding in the suspension. I was wondering if anyone has ever installed spherical bearings to replace their bushings, if someone actually makes them, and if it's worth the trouble.

Jim

link to the article:
http://sportcompactcarweb.com/projec...c_project300z/

 

Ask BicuspiD, or read this...
https://www.rx7club.com/suspension-wheels-tires-brakes-20/pillowballs-all-installed-my-impressions-looooong-312722/

 

First off, Howard that was a great post. Excellent!!!!

Second. I have the JIC FLT A2's with the 9KG 12KG spring rate. They are okay for street, unless you are on really harsh roads. Then it can become a bit uncomfortable. They are still completely streetable from a comfort level.

However, after reading Howard's post, I am more concerned that these heavier springs may actually be hurting performance rather than helping. I think I would be better of with 10KG 8KG or 8KG 6KG?

As far as the pillowballs. I wish I was more educated about them when I bought the coilovers. I might have gone a different route. They are probably unnecessary, and just ad to the harshness of the ride.

Does anybody know if the JIC's can be custom built/revalved with matching lower weight springs?

 

Yes, JIC and most other brands only offer the pillowball upper mount. Endless is a little different. They use a rubber mount of some sort.

dis1

 

“the front and rears are valved differently and they prefer that method over different spring rates.”

shock valving and spring rates are two entirely different things. The above statement is ridiculous.


“I was wondering if anyone has ever installed spherical bearings to replace their bushings”

the fd has a real racecar suspension and as such employs a bunch of spherical bearings, sometimes called “pillowball” bearings. They are a wear/maintainence item but are worth the extra effort. There are, IMO, two places where mazda elected to use rubber and should have used either a much much higher durometer (read stiffer) rubber or spherical bearing or, ala Jim, a nylon variant. I think every performance oriented fd should replace the front big fat rubber bushing on the lower longitudinal link at the rear suspension. It feeds all the acceleration and braking forces into the chassis. The second replacement candidates are the two big fat rubber differential bushings…. Nylon is the way to go. Jack up the car and you will note the diff moves up an inch before the car starts to rise. Not good.

Other than those two the fd has spherical bearings where needed. It was designed almost 100% right from the start.

“I have the JIC FLT A2's with the 9KG 12KG spring rate. They are okay for street, unless you are on really harsh roads. Then it can become a bit uncomfortable. They are still completely streetable from a comfort level.

However, after reading Howard's post, I am more concerned that these heavier springs may actually be hurting performance rather than helping. I think I would be better of with 10KG 8KG or 8KG 6KG?”

12 kg is 670…. Way too stiff….that’s 1340 pounds per inch at 2 inches of bump and your corner weighs 700 pounds. If you can swap down to 8/6 you will go faster and smile lots more. If your shocks are adj you probably will not have to revalve them.

Pillowball upper mounts truly suck on an fd. I would simply adapt the upper shock rod to the OEM rubber mount. BTW, I almost fell out of my chair laughing when I read Jim’s comment about wondering whether he could adapt his coil overs to the oem setup. This coming from someone who has truly and properly re-engineered the whole car… it might take an hour’s work for most of us and 10 minutes for him..

Howard coleman

 

That statement came from "both" Buddy Club and HKS's tech support. I was told by HKS that the HD-I's used to have softer rear springs but firmer valving. The HD-II's have softer valving and the rears are vlaved differently then the fronts and a prefered method over different spring rates. If that is incorrect, I have no idea why both company's replied the same thing.


JIC can be revalved here in socal by Ziel Motorsports but the last time I checked it was $200ea and to replace springs is $100/ea. I was going to move my rear springs to the front and buy 6kg's for the rears. John told me that would not be a problem but I do not want to pay for revalving.

 

If I had stock parts to adapt.

I just wondered if there was a "down level" JIC option that didn't use the pillow mount. I've been wondering about those things making noise. I was considering just encasing them in rubber, but you'd still have the pillow ball in the center. Oh well.


Are the rear springs the same height as the fronts? I guess it really doesn't matter, since the spring perches are adjustable, but it would be nice to have the same range of adjustability as "stock".

Also, can you buy JIC springs separately? Again, it doesn't really matter, especially if I'm going to have them powder coated. I could just buy a pair of Eibach springs for the rear and have them all coated the same color. The Eibachs are probably cheaper to boot.

 

Goes to show you then that a "big" brand name doesn't ensure the person you spoke to knows what they're talking about.

Springs and shocks do two entirely different things. You can't use one in place of the other.

From the Suspension and Handling Links sticky:

Shocks and handling by Grassroots Motorsports An article about how shocks and their behavior effect your car's handling.

Dynamic Load Transfer Load transfer explained

Smithees Race Tech Some great tech articles about weight transfer, shocks, springs and suspension geometry.

http://www.smithees-racetech.com.au/...shocktune.html

http://www.smithees-racetech.com.au/...ringsbars.html

 

About the pillow mount....Lucky me. The MazdaSpeed of mine comes w/ rubber ones. Hee hee hee....anyone envies?

 

So you think 502lbs upfront and 447lbs in the rear would be too much for the street/track? I'm looking at the Zeal B6 Model. and thats the lowest spring setting they have. The car will be driven at the road course once and while but also mostly on the street.

their lowest is 9 kg/mm - 8 kg/mm