I've made some (too many) changes to my suspension & alignment setup. As such, i'm now in a place where i'm trying to recoup as quickly as possible. Any advice is appreciated.

Since the late 90's, i've run the Pettit "Long Track" setup on 245/45R16 V700 kumhos on track and Autox. That worked well enough to be competitive in most any event. In addition, it did not destroy my street tires too quickly. I had been running that setup using the R1 Shock/Swaybars and Eibach ProKit springs.

My frist change was a TriPoint tubular adjustable front sway bar. Following this, more major changes occured. I had intended on doing one change at a time, but because one of the spokes on my 1992/PED stamped stock wheels (the lighter brittle ones prone to cracking/breaking)

I bolted on a new set of coilovers F: 11kg/mm (615 lb/in) & R: 10kg/mm (560 lb/in), and a set of upgraded trailing end and toe links. Alignment was adjusted to help with turn in a bit:
Front camber: -1.5, Front toe out : 1/16, caster +6.0, and Rear Camber -1.4, Rear toe in 1/16.

This felt ok the first day on the stock 16's but due to the cracked wheel, i moved directly to a set of 17's i had in the garage on "standby". These 17 inch wheels are running 255/40R17 & 275/40R17 (three year old Yoko A032R tires) and i find myself in a fairly uncontrolable car.

I push on corner entry, and find i can throttle oversteer _way_way_way_ too easily (stock engine/boost levels). I've since removed the rear sway bar, and have begun backing off the tripoint adjustable front bar to attempt to find a more neutral position - but that's taking a bit of time and i have pretty much only 11PM -1 AM to work on this between autocross weekends.

I was able to made some headway with tire pressure adjust ments as well,

If you look at this link from Pettit:
http://www.pettitracing.com/rx7/index_information.htm
it states that camber settings adjust pretty dramatically based on wheel size. From what i've read so far, it would seem that there is an assumption that the sidewall will be smaller when using the larger wheel. In my case, the difference is only about 1MM in the rear. That doesn't seem to be so different, and that seems to be my biggest issue. I figured that even with the same camber settings, the 275's should offer more bite than the 245's even at the same camber setting.

 

Your spring rates are too high....the rear spring rate is way too high relative to the front rate. With the 600-lb front springs, adding more bar up front is too much. Additionally, you have added a staggered tire width setup.

I am running the exact same spring rates right now, as an experiment. I also have staggered tires, but have stock sway bars. I know exactly what you are talking about handling wise. Another thing -- with those spring rates, you have to drive VERY VERY smoothly. You cannot get away with any kind of ham-fisted driver input. My advice - run softer springs, at least at the rear. I will be contacting Rishie to get softer rear springs for my Zeals (down to 8 at the rear from 10).

 

I considered getting a set of 8's as well. If i do that, i might move the 10's to the front. I think the road surface irregularity (North east) may also contribute to the problem. Although the last event i went to was an utter disaster time wise for me (out of practice) i'm generally referred to as pretty smooth by comparison to the competition.

Still... i'm miles away from a pro driver and maybe that's what the 10kg rears are confirming to the world. Still, I think i'll get another 16 inch wheel and try that before chaning out the springs.

btw, did you get the aluminums? they are very light.

 

The stock suspension, R1 or otherwise is pretty well set up. It takes a while to properly sort out a new suspension. Higher springs rates and stiffer shocks is not always faster.

When I switch to a "race" suspension to I was a little bit slower until I learned to dial it in and drive it correctly. Now it's a little bit faster than stock.

Also, three year old R compound tires are going to be all dried up and horrible with any suspension setup.

 

I expected the R tires to be much worse, but they heated up better than expected according to the pyrometer. In any event, i'll try new tires first. Thanks for the other comments. I'm just having a difficult time shaking the feeling that i could "lose it at any moment"

I'll do more sorting next weeked.

 

Any comments about why there is such a dramatic change in the posted camber settings for the 16.17 and18 inch wheels? http://www.pettitracing.com/rx7/index_information.htm I just throught there might be something to that.

 

I think it is the inherent shortening of the sidewalls and the fact that they won't give as much in cornering. So it has less to do with the wheel size, and more to do with the tire profile. You'll probably find the inside of the tire getting a lot hotter than the outside until you get set up with less camber.

Dave

 

Yeah... the Pettit camber settings for 17-18" wheels are crap! You can run less but you should still be running around 1-deg front and rear (tweaked from there) for 18" wheels. More like 1.3 deg or so for 17".

 

I had to learn that the hard way by almost crashing my car. The 0 degree rear made my car extremely unpredictable on boost. I get no abnormal wear on my tires using the stock settings.

 

I actualy have to disagree. A friend of mine is tracking an FD with 18" rims and I'm using the stock 16 inchers. He's been making careful record of tire temps and the temps do indeed seem to be most consistant across the contact patch with the less agressive Petit alignment. It seems a larger diameter wheel does need less camber. I too was sceptical... but the hard tire temp data I've seen supports the Pettit specs.