FC rear camber best at 0???
 

Hey all,

I road race my FC TII and have fully adjustable rear camber with both the rod and the adjustable dog bones along with full poly bushings. What I have found is that around 0 or even a small bit of positive camber puts my tires at an even temperature across the tread, as measured via IR after the race. running 255's back there. and temps seem the same on both pass and drivers side.

Seems a bit too straight up so wanted to know if I am looking at things right or if others have seen the same.

Thanks all.

measure with a probe and compare to the IR.
you want the core temp not the surface temp.

does your track have allot of straight?

ALSO you know the only time your tires SHOULD be at an even temp is just after a sucsessful skid pad test and tune right? especially on a gen 2 suspension.

Ok so now screw all the "data" that youve collected.

what does the car handle like? how much tire, what kind of tire, what kind of shocks springs, how much power, whats your weight, how much expereance do you have, how much difference is there between your time and the universal benchmark of a miata? is your rear steer intact?

I need to know much more, BUT i imagine your car has very little to no under steer (because you have crippled all the rear lateral grip out of the car and without knowing the front suspension settings), and if you are NA or stock turbo power you shouldnt have to much trouble with oversteer, or are at very least unknowingly compensating by not getting on the gas as much...

SO I would think this should handle about like they do stock? although ive never raced a stock genII...

didnt mean to sound like a dick. I prolly did, unintentional, but at the mere mention suspension my mental can of worms explodes...

Im subscribed...

ALSO the above is SOLELY from experience, I have never tried a 0 deg rear camber.
OH and through the polly bushings in the garbage if you are serious about roadracing...

THe only thing I can think of that would make this setup (sort of) work is if you had a street tire on (relatively) soft suspension. so that under load (acceleration) out of the corners you get a load of weight transfer and the camber gain from travel helps. but your inside tire is proly useless... lso this setup should not have very goor rear traction under breaking. as the tires should go positive from droop.

If your temps are even across the tread, you likely don't have enough camber. Remember, when you are on your cool-down laps, the tires come down in temp very rapidly. Optimal measurments would be a hot-lap and then a friend in pit lane with a pyrometer.

What you really should see is an even distribution of temps across the tread - like 165 outside, 175 middle and 185 inside (not saying those exact temps are appropriate - just using them as an example. Its what we see for Hoosier RS06's). You can tell if you have too much tire pressure by the middle reading realitive to the outside and inside. You don't want too much difference between the outside and inside because that will show too much neg camber - but the net answer is you have to account for cool down.

These guys are giving great advice. To me it sounds like you may have driven the car to the paddock, hopped out and grabbed the IR temp sensor. By then its way too late. The tires will equalize the temps fairly quickly. Do it in the pits with a probe right at the end of a hot lap. Now for the next curveball, many tracks suck for getting tire temps! Road Atlanta for example, you pull into the pits after a long fast straight and a couple quick turns then a short straight and into the pits. You won't get good info there.

Speaking of tire pressures with the pyrometer, it can depend on your tire too... I'm running BFG R1s on my TII, 225-16 front and 245-16 rear. Using a pyrometer I tuned the pressures to be even across the tread, and my tires would be awesome after about a lap and then go to shit roughly 2/3rds of the way through a 25 minute run session. A guy at an event with me running the same tires on his 911 said that a BFG tech told him to run about 41PSI hot and screw the pyrometer spread reading. After a couple of attempts I got the pressures there and while the ultimate grip seemed slightly less (butt dyno, unfortunately) and they took longer to warm up, once they were warmed up they stayed very good for the entire run group.

I will try and answer your questions in order to facilitate.

No very curvy.

Not sure how to answer the first question.

225's front, 255's rear Khumo Azenis. Have to keep it cheap to learn on the car first.

Tein adjustable coilovers.

400 RWHP approx.

Not sure of weight but approx 2900 without me. estimate 52/48

Only about 4 weekends of experience with this car.

Not sure of my time compared to others. I keep up in my group.

Rear steer elminator busings installed.

Your talking as if I can't adjust things. It takes me 10 minutes to adjust my rear camber if the jack is nearby.

Yes you bring up the point that I did have to stiffen up my front shocks later in the day as I slowly took out more and more rear camber. Generally, the car will perform with more oversteer but I was able to get it to neutral at the apex with oversteer past the apex by the end of the day.

Kinda answers questions that were racing in my mind...hence the post.

It's what the car came with. What do you suggest?

Haven't gotten into rear braking issues as of yet and this is not the intent of the setup.

Thanks,
Ben

Good point and will take it. Now the issue: Where to try the rear camber at?

Just thinking of a starting point...maybe 1 degree negative?

Kumho doesn't make the Azenis, Falken does.

Also, since you're running a stagger, this will change things, as to get even handling, you'll be needing to compromize rear grip to make it match the front, that could be why you're finding zero camber to work best.

YEP!

buy the spherical bearings for the rear, from AWR.

Delrin bushings work well on the front.

your setup is a little all over the place.

if your running 400whp and your "keeping up" in your class, theres a TON left in potential in your car...

Some things Ive learned from racing on a stagger. KAAZ 1.5 way LSD... SO NICE...
lets the big rears rotate independently under deceleration and lock back down under accel...

instead of adjusting the front shock up, try making it up with tire PSI, but if you keep with the stager i would say go up 1 kg on the front springs. or conversely 1kg down on the rear.

in the future try to keep the stagger to a minimum by going as wide as you can in the front... want some carbon fiber wide front fenders from shine? (i have some extras;)


at the end of the day, just go drive the dam car and have fun!!! but it would behoove you to turn the turbo down as much as possible to learn the raw balance of the car.

Can we safely assume that these are radial tires? If so a 20-25 deg. difference inside to out is what you are looking for and actual temp IS important. If you are not getting 180+ temps you are not getting them hot enough to make a diff or are measuring them way to late. I have seen temps 200+ and set some very fast times there. I would start with 2deg. of camber in the rear 3-3.5 front and don't change a thing untill you see temps (with a probe) of +180.

Yeah caught my Falked up mistake too late.

I have begun to realize that my stagger is not doing me that much good. I will be changing this on future tires - in about 2 sessions time.

I think a lot has to do with the driver at this point. I am still building a relationship with the car. Don't really know its limits/likes/dislikes yet.

Appreciate the LSD suggestion and will look into it!

I will be ordering a probe soon.

Wow, that is some serious camber but will take your suggestion. What you mean by "until temps 180+" is that I am finally able to push the car to its limits?

John,

Excellent starting points. John and I have extensive experience driving and setting up RX-7's for high level SCCA racing. Our cars currently own 5 track records up here in the northeast.

Tire temps are important because each brand and model has a range wher eit operates at peak performance and grip.

Head to an SCCA weekend and pick the brain of some of the ITS drivers running FC's. It will become real clear real fast what you need to do. The tires you are running are indeed a glorified street tire so some of that may not cross over but it will be a start.

I am running a 335 rear (hoosier R6) with -2.1* camber. My temps are about 35* spread (from the inside out of course) starting with 29 psi cold. I could probably do with reducing the camber slightly but it is close. I am running a 315 front tire and the handling is very neutral.

I am using the AWR camber adjusters, AWR toe adjuster rods, and the AWR spherical bearing that replaces the stock toe cam bolt.

do you mind if I ask...

what sway bars and what settings?
what spring rate?
what shocks?

what have you done with the front caster?

If you dont want to answer I understand;)

sorry to thread jack...

No rear bar, front bar is a Speedway bar (rated at 247lbs). Spring rate 650lb front 400lb rear, Koni double adjustable shocks front and rear (front is 8612 RACE insert in AWR tube, rear is custom based on Sport model, modified for double adjuster and revalved for spring rate).

I initially started at 3.5* negative camber in the front, but the inside was 20-30* hotter than the middle of the tire. I'm not sure if it's because the tire is so wide (315) or what the cause is as I know most people suggest 3*+ on an FC. I have to run around 2.5* at the front to get a good temperature spread.

Would your front spring rate not be higher than the avg. FC because of the 20b powerplant? 650 sounds a bit high.

I actually have a 13B bridgeport turbo in there now. I originally used 650/400 with the 20B, but since switching to the 2-rotor the car still feels quite neutral with the 650lb front. I just added a big front splitter and airdam, and will be extending it to a full undertray so it will be interesting to see what effect that has on the handling. 600/400 seems to be something of a 'standard' on the turbo FC's that I know of which roadrace (Carl, Brian, etc).

Great information and appreciate it. Slowly I will bring my car up to a level closer to yours but doubt if I will ever attain it.

I am starting to feel I have a bit more ammo to be even more competitive in my class.

Appreciate all the input I am getting.

Another question: Do you find the camber adjusters have less play in them compared to the dog bones and thus the need for camber increases? I ask this because the last session, I had only one adjustable in and that side had a greater differential in the tire temps even though I made sure both sides had exactly the same camber.

makes sense with the speedway up front and no rear... what type of lsd?

I like your setup. makes good sense, should be nicely balanced. do you run any toe?

LSD is stock T2 clutch LSD that was rebuilt about 2 years ago. It definitely needs an upgrade.

Toe varies for me, but either 0 or 1/16" out depending on twistyness. I finally just got the car mechanically sorted out so will be toying with the suspension more in the coming weeks.

I haven't noticed that with the camber adjusters as I had no real baseline (I've never run the car with the stock dogbones).