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I'm currently trying to fit 285/650-R18 racing slicks under the car,
because the Avon 10/21-15 keept overheating on the rear and didnt have the grip I wanted.
I sure have to work on the fenders, thats one thing:
On this picture I just put them on the car with the old setting so see how much I have to change.
In front I need 25-30mm of wheel spacers to make the wheel clear of the coilovers.
Wheels are offset 25mm, while stock wheels are 40mm, so this makes another 15mm.
So overall it is 40-45mm more outwards, which makes sense when the 285 wheels are 80mm wider than stock, the wheel centre has to move half the amount outwards...
Now 40mm change is a lot and will mess with the scrub radius a lot.
With the 15" Avon I had like a 20mm change from stock and wasnt super happy with it.
So now I'm trying to move the wheel hub 30mm outwards to keep the scrub radius near zero
and I wonder if anyone has done or seen that before on a FC?
The FC S4 front control arms give me the great opportunity to extend them at the outer ends because the bearing there is bolted on the actuall arm,
I'm already in building process of parts....
Have you looked under the front fender to see how much room you have until suspension travel sends the tire into the unibody?
Usually RX-7 GT cars that use 650mm slicks are front halved or minimum front tubbed and reinforced.
If you go that route you can play with suspension geometry without needing spacers or scrub radius.
pic is the RE Amemyia FC2000 car. i'm not sure what they ran for tires, 265 ?? 18? not the greatest pic, but they did a lot to get those tall tyres to fit
Oh good, you are already onto clearing the diameter.
For suspension work, you have to decide how far from stock you want to go and how much bad driving manners you can put up with for the grip.
Minimal work-
One thing you can do with stockish geometry is kick the strut top way in to negative camber at the top. I notched the camber adjuster, but didnt yet notch the car sheetmetal.
Next, slot the upper bolt hole on the strut lower mount and take out excess negative camber to suit desired alighnment there. I settled on 5 degrees negative camber.
This does several things-
1) moves strut away from the back of the wheel so you can run closer to stock offset.
2) moves steering axis to tire contact patch interception point further out (since a line through the strut top mount and lower ball joint define steering axis).
Together these will correct your scrub radius and increase your camber gain with suspension compression.
Oh sorry "BLUE TII" haven't seen your first post.
Yeah it is a big step from 15" to 18" and in tire diameter from 550mm to 650mm with all the negative effects of taller wheels, weight , ride height , gear ratio...
But these are the sizes I can get my hands on easily, and the 15" Avon didnt give me much joy.
Final test was this year on Lausitzring when in some corners I was even faster with my old R888s compared to the Avons.
And the Avons died in the rear from overheating and to much camber ( they dont like camber bc they are diagonals)
So I decided to make the big step.
Yeah I alread cut quite a lot, but I still dont know if it's enough.
I cant go tube frame with some classes, so I just want to cut away and close the beam with sheet metal like they did in the Amemiya pic.
I know on stock cars nowadays the suspension makes like 80-100mm travel upwards, so I hope like 50mm is enough for a racecar...
Originally Posted by BLUE TII
Together these will correct your scrub radius and increase your camber gain with suspension compression.
Sounds interesting, do you have a picture of your suspension setup?
I know on stock cars nowadays the suspension makes like 80-100mm travel upwards, so I hope like 50mm is enough for a racecar...
i would think that is about right, or you could achieve it.
the full spec for the RE car is here, REJ{ FC3S щΎR
if you look on you tube there is a compilation video, and then video option has the build in different parts, and there are more parts than what was in the compilation
I remember those videos, but was still good to watch again.
Looks like they just went with wheel spacers in front, but also their tires are "only" 255s
As I said I'm already in making the parts.
To make the control arms 30mm longer I did put in a alu block with 30mm offset holes.
So I can bolt down the outer bearing 30mm more outside.
To get the 30mm offset between the coilovers and the wheel carrier I needed someting more complicated.
Luckily a friend got a "new" big milling machine:
A good opportunity to practice some milling.
I'm happy with the result, for the fact that they are my first milling-parts
I'd personally feel more comfortable with custom tubular control arms with a longer length than a bunch of bolted together extensions.
It truly looks a bit odd, but there is still the opportunity to change that in the future if the overall concept proves itself.
Instead of making those coilover extensions I could also make new wheel carriers, but how long would that take...?
I've got the idea of racing the car every year, I dont want a garage queen, thats why I sometimes have to do compromises.
In theory I could even switch back to "stock" at the racetrack, if I bring suitable wheel spacers ...
By the time the body work on the left side is done.
Looks like a lot of camber
I did something similar to the spindle mount, but only 2mm on one side (bc the car is bend :P), but it seemed to slide back in the slot.
Did you do something to prevent this?
And I think by moving the control arm outwarts I'm getting enough camber.
I did a test fit and had like -3 deg , and still room in the top mounts.
Let's see...
With stock hardware tightened to spec mine only moved when I tried to bend the car (wrecked)- but I was only using max 255/40-17 DOT R tires.
If you want to make sure it wont move with wide tires or hitting curbing you can put spacers in the slot and fender washers covering the outside
of the slot- so the bolt is captured.
On the 225/50-16 RS3 I ran -5 degrees camber (pictured).
On 255/40-17 RA1, NT01, RC-1 etc I was running -2.5 to -3.5 because with the shorter stiffer sidewall braking was horrible with any more front camber.
I was not unhappy to leave the strut life behind...
No, I believe the poor braking performance with low profile tires was due to decreased contact patch from negative camber.
See the light under the 50 series 225/50-16 at 5 deg camber in my pic?
It was more daylight with 40 series sidewall 255/40-17 from the shorter stiffer sidewall.. Plus since the 40 series sidewall was stiffer there was less distortion under load transfer of braking so the contact patch didnt spread under braking as much.
My switch from strut front suspension to double wishbone came when I started racing my rx-8 and FD rx-7. Also, they fit 18x11 +45 at near stock offset (50) and 315/30-18 on stock body. They handle/drive like stock with that fitment.
I had raced my nationals racer buddies CP Fox body mustang which had all the suspension work and wide Avons. It drove like a real shitbox and I knew then I didnt want to go that route with the FC.
Yeah I get what you mean, I just hope it is worth the time I am putting into this.
I also had to make a longer bracket for the torsion bar, which I connected right after taking this photo:
The wheels can now be put on without any wheel spacer, but still they need to be covered by the fenders.
I went a little wild in my mind, so I came out with this:
It is CFK and in the pic just test painted with a roller
Still needs to be fillered and sprayed and will be around 2kg or 4lbs
The car was just done for Reisbrennen , Germanys largest asian car meet, and I could do some laps on the Lausitzring.
The steering feels super easy, you really dont feel the 285 slicks so I think the scrub radius thing works out.
Also no pulling to one side at any time, but I have to admit it was on the racetrack, a bumpy one, but still a racetrack.
I did some testing with the camber and tire pressure, and decreased both during the testing.
But I think I could have gone lower with tire pressure, boost was still reduced in lower gears from running in the wet last time and also the aero wasnt setup.
So laptimes werent that great, but there were also a lot of slow cars on the track.
In the end it was a successful testing of the new setup, with a lot more potential to come.
And it turned out nice looking. A photograph asked me and a buddy with a 20B FD to set the cars up for a photo:
Would be cool to go there next year or so, never been to the event to be honest.
Ever had issues with noise limit?
Yeah come there, at Reisbrennen there is no noise limit, thats good.
There is always also a drift event and a drag race at the end with some real drag cars, so...
No noise limit? Then I'll bring the muffler-delete pipe with me
But jokes aside, most are with a 95db limit. Zandvoord is avarage so one can stick out a little when the rest is under. But others have strict 95db limit which is a challenge. It has been quiet a while i've been on the track but I am slightly worried lol
Yeah I'm also worried, I want to go to Anneau du Rhin in France and they have a dB limit of 100dB.
Last time I had 101dB and they let me drive , but this was only with dB-Killers in the mufflers, which limits the engine to 350 bhp
Made a new rear muffler because I thought the old one was toast. But I was wrong.
Wanted to play around with some inserts or perhaps other muffler designs but need to get the car back on the road first.
12-22-22, 01:55 PM
