cbrinega

The purpose of this thread is to collect the knowledge of the options for FC suspensions. Please contribute your technical knowledge and personal experiences. The majority of the information below comes from my reading on this site over the past couple of years.

Search Results:

Here is an old thread (2001) in the 2nd Gen Archive about suspensions (springs in particular):
https://www.rx7club.com/2nd-gen-archive-72/looking-aftermarket-spring-advice-12139/

Here is a more recent thread with some useful spring and strut (shock) information and opinions:
https://www.rx7club.com/showthread.p...ght=Suspension

Summary of Existing Information

Here is a list of information about what are some of the best bang for your buck options.

Daily Driven Suspensions

These suspension combinations are common ones I've read about and seen on daily driven FC RX-7s. The suspensions are non-adjustable, have conservative spring rates and drops, and are the lowest cost options.

Eibach Progressive Rate Springs with Non-Adjustable Shocks

This setup gives a 0.75 inch drop with a slightly softer than stock initial spring rate (around 15%) and a much higher compressed spring rate (almost double).

Tokico Springs with Non-Adjustable Shocks

This combination has a 0.75 inch drop with a 20% increase in spring rate. The spring is a linear rate and is currently difficult to purchase.

Racing Beat with Non-Adjustable Shocks

This combination has a 1.0 inch drop with a 20% increase in spring rate. The springs are linear rate.

Non-Adjustable Struts

Tokico HP
KYB GR-2 and Gas-A-Just

Mostly Street and Some Track Suspensions

These suspensions include adjustable struts and more variety in the spring rates. Note that different drivers can adapt to different levels of harshness, and the split between the amount of street versus track driving is also a factor.

Tokico Springs with Adjustable Shocks

This combination was used by the late GTUs of RarestRX and provides a modest drop 0.75 inch and a 20% increase in spring rate. His car certainly had its share of spirited driving and appeared to be okay on normal roads too. (I've only seen it in photos though.)

Racing Beat Springs with Adjustable Shocks

This setup gives a 20% increase in spring rate and a roughly 1.0 inch drop. The suspension should be nearly identical to the one above but with a slightly lower stance.

RSR Down Springs with Adjustable Shocks

This setup gives a drop of 1.6 inch and 1.2 inch (front then rear). Spring rates are 198 and 163 lbs/in (front then rear) and are in the 50% to 80% range of being stiffer than stock. This amount of lowering may require camber adjustment, but I do not know for sure.

Ground Control Coilovers with Adjustable Shocks

This combination provides custom spring rates and custom ride height. Care must be taken with using this setup with certain struts as not all of them can handle extreme lowering.

Adjustable Shocks

Tokico Illuminas
KYB AGX
Koni Yellow

Competition Level

Linear rate springs in the 400 lbs/in in front and 300 lbs/in rear (note that stock rates are around 110 lbs/in).
Adjustable shocks.
Possibly coilovers and full camber adjustment.

Possible Springs

Eibach Linear Rate 2.5 inch Diameter Springs (available in custom rates and lengths)
RSR Race Springs

Possible Coilovers

Zeal
Silkroad
Tein
Ground Control?

RX-Ben

I'd like to add my setup to that list. I think this is the most popular setup for racing, I don't think many are road racing with Tein/JIC/Zeal etc. Maybe in Japan, but the Koni or Bilstein/Ground Control combo is what the racers generally use. Or a full blown Penske package, but that is pretty excessive.
This is not the typical Koni/GC package. You need to buy a custom strut body for the front from G-C, and then you can put in the generic Koni/Bilstein insert. This opens your options to a wide variety of dampers, and spring choice is unlimited as the system uses 2.5" springs. Combine these with the front camber/caster plates and you have tons of adjustability.
In the rear I have the Koni "sport" damper and a G-C coilover system.
I have nothing to say about this setup as the car is still on 4 jacks.

Don't ignore the bushing issue when you talk about FC suspensions. The front lower A-arm has so much binding built in that it makes no sense to me(though I don't claim to know anything about engineering a suspension). The large rear bushing in the front a-arm causes a bit of binding, and tightening the front bushing to factory specs will literally lock up the a-arms with 200+lbs of resistance. I'm trying out a UMHW (like delrin) large front bushing in hopes that it moves more freely, and using a delrin on the small front mount with a lock washer and lower tightening torque. If there is still significant binding I may be going to the AWR bearing setup.
On the rear bushings, I'm using a delrin bhsing for the trailing arm (though there is a bearing setup available). I had to cut and reweld the mount on the subframe to get the bushing to fit freely as they plain wouldn't fit otherwise, no matter how hard I beat things with a hammer. This is a very very minor bit of fab work and if don't have a welder you could bring it some place and it would take them about 2 minutes worth of welding. I don't know how well the stock or poly bushing fits in the receiver on the subframe, but it may be worth it to enlarge the receiver to better accomodate those as well.
I used delrin/umhw bushings for the large rear subframe-chassis and the diff-chassis mounts as well, in hopes of cutting down on axle hop/broken axles. The install is pretty straightforward on these- press out the old items, chip away any rusted metal and the press in the new ones.
Also, replace the DTSS with a solid setup, unless you like the DTSS "feature."

Finally, in back there are a couple other items that AWR makes to improve the odd suspension layout in back. They make toe adjusters which are something of a pain to install, but actually pretty easy if you have a creative and highly competent friend who has access to a Bridgeport machine. Also, the AWR camber adjusters are a very good idea as they allow L-R changes and you can make camber changes pretty easily. They also make roll center blocks but I have nothing intelligent to say about them (yet).

I have no idea why Mazda didn't do a simple double A arm on the RX7...it would've been so much simpler. I think it must've been a product of mid 80's thinking as the Porsche 928 also had a "reactive" rear suspension.

Ben

RETed

MacPherson (front) struts is still one of the more compact and cheapest type of suspensions.
Trailings arms are also more compact that double wishbones.
"All wheel steering" was a buzz word back in the 80's.


-Ted

RX-Ben

The RX7 suspension is no more compact that the double A-arm setup on my old Honda. And the only upgrade the Honda needed was camber adjusters up front. If an econobox like a Honda Civic had enough space and $ to put a double a-arm setup on their car, why didn't Mazda have an extra few dollars (and that is how much it would've cost them) for a second a-arm up front?.

Not that a front strut system is too bad...the new M5 and all 911s have it as well. Anyone have any idea how their designs differ from an FCs?

Ben

RETed

MacPherson strut just needs a lower A-arm or equivalent.
The double wishbone needs TWO A-arms of equivalent.
Physical size wise it might be "more compact", but it takes more parts to complete.


Oh, don't even bring up 911's and their suspension.
A good friend who works on those things for a living always bitches about how stupid the suspension is on those things, but Porsche has developed them to much that it all works for some unknown reason...


-Ted

RX-Ben

I realize the differences between a McPherson and a double A arm, but have you seen the upper arm of a Honda Civic/Integra? I bet it costs less than $5 for Honda to make them. And it takes up practically zero space.

Any idea what Porsche and BMW do differently (if anything) to make their front suspensions work so well? I do see that Porsche doesn't load up with front suspension with a few hundred pounds of bushing binding. What makes their design any more stupid the the FCs?

Ben

RETed

Yes, I've worked on Hondas before.
It's all cheap, stamped steel pieces.
If you wanted to build an RX-7 with stamped steel suspension arms, be my guest.
Mazda went through a lot of trouble with hose squeeze cast aluminum arms for less weight and strength.


Porsche?
Throw enough German engineers at a pig, and they will make it fly.

BMW?
The key is their valving in their shocks - this is what I got from a very good buddy of mine who did damper rebuilding as a profession.


-Ted