I do see lots of gab on the internet about setting corner weight. Weight distribution is important but you generally don't need to scale your FD. It was designed with close to perfect longitudinal weight distribution. Weight of course is one of the keys to the FD's phenomenal performance... approximately one thousand pounds lighter than the "sporty" Mustang or Camaro. There really are only two important modifications with regard to weight:
remove as much as possible especially evil front weight
move as much to the rear as possible.
Let's take our FD to the (road racing) track for some excercise:
I recommend 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 (30 F/27R) and run 3-4 laps. Pit, check your tire temps immediately, and your pressures after… record all 3 temperatures from each tire. You want 10-20 degrees more temperature on the inside third of each tire versus the outside third. Camber is easily adjusted at the track. Tire temperatures will lead you towards both proper camber and starting tire pressure.
Set the camber not forgetting to compensate for any floor angle.
Here’s the car under heavy braking from 143 mph downhill into turn 5.
Many of the cars I raced against were well prepared and had adequate resources. Often the majority of the GT3 grid was under a second apart. GT3 is a serious competitive class.
Nevertheless, my yellow rocket set lap records at every CENDIV track and ran under the lap record at Road Atlanta. Lots of National wins, including a couple of June Sprints and a second at the Runoffs.
While there were lots of tricks on the car the accomplishments came from doing the basic things properly and that is my most important message. It is also the primary concept I apply to the wonderful RX7 FD.
Let’s get to it.
The FD is a magnificent road course car. My friend Frank 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 hundred thousand $.
We settled in the middle and off the car went to my absolute favorite chassis guy Craig Carter. Craig did an entire suspension plot of the car.
Craig 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 Trans Am 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. 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 pit stall 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 off track excursion.
To go fast you need to trust your car.
Trust comes from direct dynamic feedback between straight line and fully laterally loaded on the springs and swaybars. The stiffer the car is sprung the shorter the time to full load and the less feedback. A properly sprung car will provide feedback allowing the driver to more easily drive to the limit. The limit, regardless of spring rate due to the camber curve will be the same so there is no speed advantage to overly stiff springs.
Which brings me to subject one… lateral weight transfer. Ideally you want equal weight on your four 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 its value.
There is a major point of confusion here that needs to be cleared up so we can get tuning.
There are only two items that determine total lateral weight transfer…
Center of gravity
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.
By the way, 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 its 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 fender well with body roll, the suspension adds negative camber thus keeping the wheel properly cambered to the track.
The specific amount of dynamic negative camber gain on bump engineered into the FD is pure racecar and is one of the main reasons why the FD is such a track terror.
Some cars need to run huge springs and bars to kill roll because their suspension 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 (4.7 KG/MM) and 195 pounds (3.5 KG/MM) in the rear. These are my numbers from my Longacre Digital Spring Checker. Just FYI, with linear rated springs the effective rate increases with contraction. The second inch of the FD front spring is 526 and the third is 789…
I ran 432 front and 378 rear. (7.7 KG and 6.7 KG.) and was delighted with this rate. From lengthy successful experience on track as well as street I recommend 8/6 as optimum. Eibach offers 8 inch free height, 2.5 inch or 60 mm inner diameter springs that may fit your coil overs. Swap in a 475 set front and 400 rear.
I ran 10/8 at the Texas Mile and would run them IF I was using race (only) tires solely on track. Plainly put, 10/8 springs on an FD BOUNCE over the bumps and no shock absorber can do anything to reduce the spring rate.
Remember, both rates transfer the same lateral load. The higher the rate the harder it is to drive at the limit.
I see numerous coil over options for the FD with matching front and rear rates.
Note that the OE trim is 263 front and 195 rear. The rear rate is 74% of the front. The bias relates to the FD being a front engine rear drive car and it seeks to deliver increased rear grip to the driving wheels. To the extent you change the rear from the OE balance you decrease rear grip and end up with a tail happy car. Remember I said job one was to hook up the rear end.
My 8/6 optimum rate works well as factory rate is 74% and 6 KG is 75% of 8.
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 OE springs (and perhaps shocks) with aftermarket.
Replace the OE springs and shocks w a unitized component known as a coil over.
Both work very well if you select the right hardware.
While there are a number of options I have been extremely happy with the Eibach Pro Kit spring set. 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 RX7club classifieds, these extremely high quality springs TRANSFORM the FD.
Do not discount this easy to install option.
Tein also offers a spring (only) option.
S Tech is 440/320 and H Tech is 390/290
Note front and rear spring balance between these three options…
Rear as % of front
Eibach Pro Kit 73%
Tein H Tech 73%
Tein S Tech 74%
With a simple spring change, retaining OE shocks might just blow your mind.
Stock shocks work with the simple spring change. 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 and Tein springs.
There are various (Koni and Bilstein my picks) 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 of 10Kg or more or equal front and rear rates.
Jeff Segal in the July 2019 Road and Track makes the point:
"There's this misconception that a track car has to be stiff and harsh and brutal. That's not the case. When you look at some of the most dominant race cars out there- for example the Corvettes racing in the GT LE Mans class... even the untrained eye can see the Corvette is soft and compliant but with enough control that it's not sloppy."
Jeff "has raced professionally for 12 years with wins at Le Mans, Daytona and Sebring among others, usually in a Ferarri."
The real reason why a number of “well regarded” brands of coil overs are only offered with overly stiff rear springs is that the shock body is not long enough to provide the travel from a 6 KG spring. In order to reduce rear travel we see 11 and 12 KG rear springs which may be fine for drift only but are a disaster for anything else.
It is really easy to make the wrong decision on coil overs so please do your homework.
I recently worked with Fortune Auto and can help you acquire an exquisitely engineered Fortune 500 featuring Swift 8/6 springs.
Moving on from spring rates, there’s the “pillowball” upper coil over mount issue. In a word, don’t.
Just to be crystal clear, the entire car rests on the upper spring mount. The upper mount of the OEM spring contains a rubber insulator. This insulator helps absorb almost all of the unwanted vibration. There is not one bona fide 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, pick a set that retains the insulator such as the Fortune Auto offering.
Please email me (firstname.lastname@example.org) for info.
Swaybars are always an excellent way to control roll and tune for over/understeer. A properly selected swaybar allows the springs to be a bit softer thus allowing the tires to spend more time in contact with the pavement.
I run 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 aluminum trailing arms. Adjustability comes from varying the pickup point on the trailing arm and also by sliding in another (straight) primary bar with a different wall thickness.
Mazda ruled Porsche for a number of years winning the Daytona 24 Hour in 1979 followed by a consecutive string of 24 hour GTU wins from ’82 thru ’93!
While that was approx 40 years ago the current DNA of Mazda as a radical engineering company remains today. 2019 introduces Mazda’s homogeneous charge compression ignition, or HCCI: in essence it lets a gasoline engine behave like a diesel, vastly improving its efficiency.
Make no mistake, the same radical aggressive engineering DNA within Mazda (diluted during the Ford minority ownership years/RX8) created the FD which if closely inspected is a radical car.
After 14 seasons racing piston engines in SCCA’s very competitive National GT3 class I switched to rotary for the 1983 season. Excepting the LeMans winning 787B, I bought, arguably, the most seminal Mazda racecar ever… Roger Mandeville’s 1979 IMSA season winning RX3.
I purchased it at the end of the 1982 IMSA season and Roger spent part of the ensuing winter modifying it to GT3 specs
Which lead to this:
The pyrometer will tell you the correct tire pressure for each corner of the car.
Let’s assume after 3 or 4 laps your tire temps are as follows:
Left Front Right Front
170 165 165 165 150 145
Left Rear Right Rear
145 155 155 135 150 145
Average Corner Temperature
Since the front has 159.5 degrees temp and the rear 150 the car is modestly understeering or pushing. Modest either way is O K and a driver preference.
First let's address tire pressure.
Left Front We add 170 and 165 (inner and outer temps) divide by two and get 167.5. We have 165 so add one pound of air.
Right Front Proper middle temp should be 155 so add a pound.
Left Rear middle should be 150 so remove a pound.
Right Rear middle should be 140 so remove two pounds
Next up is camber.
We want 10 to 15 F degrees hotter on the inside.
Left Front The all important front Left tire is the reason the car is understeering as it cool on the inside. add one degree negative camber.
Right Front just a touch too much inside heat. reduce negative camber by one half degree.
Left Rear temperatures are perfect, no change.
Right Rear add one degree negative camber.
Proper optimized setup is a double whammy. Not only will the car be seconds faster but it will be easier to drive!
As you can see, you do need a pyrometer and a quality tire guage.
Talledaga infield traffic.
A night tire and driver change at Daytona.
Roger’s RX3 wins led to this:
The above picture is from my first National Mazda win at Blackhawk Farms in 1983. Note the small 13 inch wheels which were required at that time. Given the small diameter, Roger sourced a set of rotors from a Tyrell 6 wheel F1 car which significantly upgraded the stopping power. Later in the year I set the lap record at Road America at 2:36.0 as well as won the June Sprints and placed 4th at the SCCA Runoffs at my favorite track, Road Atlanta. 1983 marked my switch to Mazda and I have been 100% rotary since.
The Central Division of the SCCA is the most competitive SCCA Division and includes the following tracks:
Road America Elkhart Lake, Wi
Blackhawk Farms, South Beloit ,Il
Brainerd Intl Raceway, Brainerd, Mn
Indianapolis Raceway Park
Mid-Ohio Sportscar Course Lexington, Ohio
Take a close look at my 1989 version of Roger’s IMSA winner… the only thing remaining is the roof and windshield. And what was the result of such butchery?
2:23.6 at Road America despite the SCCA changing the restrictor on the Weber dual downdraft from 50 mm to 38 mm! Here’s the Parade Lap of the Road America June Sprints…
Toe is easily set with a laser/mirror setup.
Here’s Roger leading Jim thru the infield at Daytona. I attended the 1982 Daytona race and it seemed like the entire 50 car field was a train on the back straight at over 150. Nose to tail drafting.
Here's where you measure
It is worth noting that I took all the scalps at Brainerd with the stock front bar and no rear bar. Repeating again, the rear needs to be soft/compliant to enhance traction.
That’s why my recommended street tire pressure is 30 front 27 rear.
Mazda went a little crazy lightening the front swaybar mount. It has lots of swiss cheese lightening holes… it is probably fine with the stock bar but when you upgrade to a stiffer bar you MUST replace the mount. I strongly suggest you contact SakeBomb for beefier well engineered mounts.
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 just 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 leads to a broken LSD. Nylon works for me.
I believe there may be a higher durometer (stiffer) bushing available. Check with RX7.com in Fort Worth,TX or Pettit Racing in FL.
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. Again, larger rears help hook up the power.
There are many stickier 100-200 UTQG tire options available. Tires featuring V tread look good at the Drive In but you want tires featuring circumferential grooving.
That’s about it for the hardware let’s move on to setup and tuning.
Chassis setup is YUGE. 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 get go to get a complete printout of the before and after.
Tire pressure 30 front 27 rear set before alignment
Ride height if you have coil overs should be set at 25 inches at the top of each wheelwell. Ride height MUST be set before alignment.
Fifty car fields (count ‘em) from Daytona (pictured) to Mid Ohio to Laguna Seca featured bumper to bumper and fender to fender racing. Factory money poured in to the IMSA Champion Spark Plug Challenge and no wonder, as the industry needed to sell the newer smaller cars after the 1973 world oil shutdown.Mazda owned the series, garnering season championships in 1978 with Walt Bohren, in 1979 with Roger Mandeville and in 1981 with Jim Downing. Jim (63) is on the pole in this picture and Roger (83) is 4th as the field takes the green.
A careful study of this picture should further cement the case for our beloved rotary.
My 12A Daryl Drummond built motor running really small 38 mm carb restrictor chokes gridded ahead of every car in the photo on a FOUR MILE (read top speed) road course. Both the tube frame V8 GT1 Camaro and the highly modded GT1 Porsche 911 are looking at my taillights along with more than 30 other GT1, GT2 and GT3 cars on the backside of the hill.
How did I do it?
By over-engineering of course.
While there isn’t a lot on the exterior that gives away the over-engineering aside from the Wide Five wheels and magnesium hubs should you be able to take a closer look you would find:
Cockpit adjustable ride height
(During the race 65 pounds of fuel are burned changing the balance. A few twists raises the right rear ½ inch and restores original corner weight)
Mandated solid rear axle has 1 ½ degree negative camber. Now how did we do that?
Speedway Engineering Quick Change center section, Watts Link (under the center section) and hollow axles complete the rear. My quick change rear gears were the first run in GT3. Everyone told me they would not work as they would absorb too much power. Everyone runs them today.
60 pounds of lead in the right side rocker panel delivers faster speed thru right hand turns.
Daryl Drummond built dry sump 12A. The block of motor is literally 2.5 inches from the pavement. J ports deliver power (only) between 7000 and 10,000 RPM. 12 quarts of oil are onboard with heater on dry sump tank so as to have proper oil temperature on first lap.
Saenz adjustable ratio 5 speed clutchless transmission. Transmission gears changed at different tracks so as to be at 7000 RPM exiting the slowest corner.
Quartermaster clutch, flywheel and aluminum driveshaft
Cockpit adjustable front swaybar.
Cockpit adjustable brake bias. JFZ brakes.
Sponsored by Hoosier Tire. Hoosier generally arrived at each track with two different compounds specifically for my car.
Suspension engineered by Craig Carter. Look him up.
Double adjustable Koni aluminum coil overs.
Tube Frame chassis with all plastic (except for roof) body.
Pressure bleeders and special sauce on the tires led to 7 poles in 12 races in 1987
Lots of small items that add up, like the window net on the passenger side…
Much of what I learned re suspension/chassis and brakes comes from short track, circle track technology. Almost all the suspension hardware was short track. My motto is go where the knowledge is..
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.
Should you wish you can do it all in your garage with a few tools.
First buy a 6 foot square tube of aluminum and a couple of cheapie ¾ sockets.
Place them across the floor to identify any slant which you will need to compensate for while setting camber. Buy a Smart Camber gauge, remove the digital angle finder and place it on the square tubing. You now have the angle of the floor.