Suspension setup on my FC RX-7...

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VinnyV81

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Hello all,

I am a newbie to the site and new to the sport. So with that being said, I have a few questions about the setup on my car.

I went to a PDX a few months ago and it was my first time in a RWD car. On the second lap of my very first session, I managed to spin out 180 degrees and go off the track 4 wheels into the grass.

I know that it was probably because I am new to this type of car that it was probably the reason why I went off, but I also remember the car going sideways and feeling that no matter how quick I got on the wheel to correct it, I felt like I had NO control of the car as it was coming around.

I did have an experience later on in the day where the car got a little unsettled in another turn, and I was able to recover-but I was wondering if there was anything I could do to the setup to make it a little more predictible should this situation ever come up again.

Any suggestions would be greatly appreciated.

-Vincent.
 
Hee hee. Boy does that sound familiar. Been there, more times than I care to remember. This car is known for oversteer issues.

IMO, this is a difficult issue for someone starting out to get a handle on. Lots of possibilities.
Car setup issues:
  • Is the rear steer mechanism defeated? From the factory, the suspension adds rear toe-out under side loading. You want to eliminate this.
  • Are all your suspension members straight? I had a bent rear toe link.
  • Is your rear toe set to at least 1/8" toe-in?
  • Have you checked the rear thrust angle?
  • Is your rear swaybar removed? Most of us run without one.
  • Spring rates? Mine are 400F 275R.
  • Cornerweights?
  • Tire pressures? I have to reduce my rear tire pressure by 3 PSI to tame the oversteer.
  • Too much rear brake? I've got an adjuster to reduce rear braking.
  • Tire type/condition. Old tires make my car very loose.
Driving technique issues:
  • Lifting while cornering. If the car is properly balanced, you need to be on the throttle through the corner to maintain rear grip. Lift and it'll come around. Don't even think about touching the brakes.
  • Downshifting while braking without rev-matching. This can break the rear loose.
Experience - the more you do it the easier it gets.

If you share more details we may be able to help.
 
Okay, well here are the details on what I have done to the car.

-Full ISC Racing suspension-non adjustable billstein's, 400/250 springs.

-AWR Rear steer eliminators

-ISC Racing Front sway bar

-Convertible BBS wheels with Falken Aezenis RT-615 205/50/15 tires (newer)

-ISC Universal camber plates

-ISC stainless steel brake lines

-Clutch type LSD with stock 4.10 gears

-Full Five lug swap with Hawk blues(pads to be installed soon, no ducting installed yet)

-1/2" Flatout Motorsports spacers in front 1/2" universal spacers in rear with ARP long studs all the way around.

-AWR single rear camber adjuster

-Rear sway bar is removed

-ISC dual pass aluminum radiator with 16" 3,000 CFM Electric fan

-ISC oil cooler with -10 AN lines

-New stock OEM Exedy clutch with stock flywheel

-Stock S4 motor with full S5 Intake manifold swap

-RB header (fiberglass wrapped) with Full ISC 3" exhaust

-Walbro 255 lph pump with aeromotive riseing rate FPR, stock lines

The suspension setup is -2.4 degrees in the front, and about -2.5 degrees in the rear, off by .3 degrees on one side because of single adjuster. I'm running about -8 degrees of caster in the front on both sides. I'm running about .3 inches toe in on the rear, and .3 inches toe in on the front(should be out but we messed it up). The tires pressures that day were on 35 psi, which is probably a bit high-but I was worried about the tires rolling in the corners. Plus I have nitrogen filled tires so I didn't want to let too much out and then be screwed...lol. Also, I do not know how to measure the rear thrust angle.

The one thing I can say is that I have NOT had the car corner weighted. Unfortunately, I could not afford to get that done by a pro, because of all of the money that I had to spend to get the car where it is at now. So basically instead I used the ride height rules for IT which is 5 inches from the lowest point of the rocker panel. And I added 1/4 inch for the rear, because of talking to other guys, I knew that the car is supposed to sit a little high in the rear. We did the ride height adjustment with me in the car. Me and my father are working on building my own set of scales so that I can do corner weights myself in my own shop.

Also, I have not even attempted to do any adjustments to the front bar on the car. When I put it on, I basically put it to where the heim joints would bolt onto the lower control arms with the tires off the ground. I'm sure that they need some adjustment, as on one side I had to run it down a little more to get the hole to line up.

I was also thinking, does anyone run power steering in IT? I thought that maybe that would help out. I have a full power rack off of my parts car that I could throw on, I thought that maybe having that would help me to react a little quicker on the wheel instead of man handling it....lol.

I think I've covered everything, if I think of anything else I'll add to it. Paul rode in the car with me and said that everything felt pretty good, except for the brake pads which I am resolving this week thanks to some slightly used Hawk Blues that I got from Mark B. Thanks Mark! Again, thanks for the help guys.

-Vincent.
 
Last edited by a moderator:
Are you running the ISC speedway bar?

I have virtually the same suspension on mine with the speedway bar up front.

Is that -2.5deg of camber on the rear? that could be your problem....
 
Yes, I am running the Speedway bar. And yes I am running -2.5 degrees of camber in the rear, but that was per Mike at ISC's instructions...
 
Loose is fast in a RWD car. If your car is setup by a known and trusted expert and nothing is broken, I would run the car a couple more events and see if you can settle into it. And remember, don't lift!
 
Thrust angle is the direction that the rear wheels point relative to the axis of the car. My homegrown method of checking it is to put a 4' level on top of the toe plate and visually sight from the rear. Check that the sight line to the front tires is the same on both sides.

Other than that, I agree with all that's been said. BTW, sounds like you've got a nice car.
 
Well thanks! It may not look like much right now, but I love the car and currently it is alot faster than I am...

I appreciate the advice...perhaps I am running too much negative camber? And also, since I'm running a smaller tire-shouldn't I come down a bit on air pressure? Or will this just make the "snappy oversteer while on the limit issue" worse? LOL.

I know I sound like an ediot and it is probably all in my head. I think that the main reason for my spin was because I didn't get all of my braking done before turning in. I was used to doing some braking while cornering in a FWD, but in a RWD this is bad.

Also, what's the secret for a smooth transition from the brake to the gas? That was something that both of my instructors said I was having a little problem with. To me, it feels like if I go right back into the gas as soon as I turn in that I would be spinning the car. Should I back off on corner entry speed a little so that I can feel better about getting back to the gas?

I think alot of this is the fact that I've never driven a car that is so "direct feeling" either.

-Vincent.

P.S.-Answer to the power steering question?
 
Vinny, I run against FC RX7s in ITS, they are great cars. I think most of the guys I run against greatly prefer the manual steering. I'm pretty sure no one runs power.

I also wouldn't worry too much about the smooth transitions from gas to brake. That is an HPDE "trait" that frankly you need to lose when you go racing. You do need to be as smooth as possible, but honestly, in an ITS car (particularly a low torque one like an RX7), you need to be full on the throttle, or on the brake -- for the most part.

I don't know much about handling setup specifics for your car, although it APPEARS to me that your spring rates are a significantly low all around, and you should lose the rear sway bar.

See if you can get Racing Ralph or Steve Eckerich to chime in.
 
I appreciate the advice, and I can understand what you mean by full on throttle and full on brakes...lol. Good to know that my manual steering is good. And just so everyone knows, I did ditch the rear sway bar (it was pretty much worthless anyway).

I took the car to my first autocross this past weekend, and wow-what an experience that was. I don't think there are a whole lot of autocrosser's here, being as that most people on the forum are wheel to wheel guys, but I was impressed with my performance on my first time.

The car was all over the place, and I used the brakes way too much, and I missed the same gate TWICE in the first two runs, but all in all it was a learning experience. I don't know how effective my car will be in autocross, but for now that's all I can afford. I let a friend drive the car and he ran about 5 seconds quicker than I did, so it's mostly me...lol. Trouble is, I have to run the car in SM2-which basically has no rules...haha.

I guess my next step is a roll cage and a better seat. That was one problem that was pointed out to me at the autocross event. The seat that I have, has very little adjustment, and is way too high (helment hits roof...argh!) So I guess I need to go ahead and find me a good, one piece, possibly FIA approved racing seat and I need to sell the seats I have. They would make great street car seats (black vinyl, mazdaspeed logo, correct sliders). I need something that is inexpensive though (best bang for buck). Any ideas?

Thanks for the advice gentlemen.

-Vincent.
 
VinnyV81 said:
I need something that is inexpensive though (best bang for buck). Any ideas?
Click to expand...

Cheapest option - Momo Start $361 shipped, FIA seat

VinnyV81 said:
...perhaps I am running too much negative camber?
Click to expand...

No. 2.5 is about right.

VinnyV81 said:
And also, since I'm running a smaller tire-shouldn't I come down a bit on air pressure?
Click to expand...

You are looking for hot pressures, so that will depend on the tire and starting pressure. Each DOT R tire has a recommended hot pressure range. For example on a Hoosier R6 I go for about 37PSI hot all around, usually starting at 29-31PSI.

VinnyV81 said:
Also, what's the secret for a smooth transition from the brake to the gas?
Click to expand...

A 2 day class with http://www.motorsportenterprisesracing.com/
Runs about $1500, when I did it Jason Saini and Eric Foss put it on. There was only 3 of us students. Both guys are pro drivers with numerous wins and championships to back it up.

VinnyV81 said:
P.S.-Answer to the power steering question?
Click to expand...

No PS.
 
Hopefully you have changed the front toe after the first mess up when you set it to .3 in. If you get it to around 1/8" or so out you will probably lose the oversteer. I think that you are understeering so bad that when the fronts finally got grip the rear had less, so you had oversteer at the exit caused by understeer thhrough the turn. Without corner weighting and hooking up the front bar the way you did, the whole setup is an unknown with regard to crossweight. At least hook up the swaybar endlinks with the car on the ground so you get rid of the preload.

matt
 
vinny , check out the set-up for rx-7 on the mazda forum. this is the set-up that i start with at most of the tracks in the southeast. you can fine tune it with tire temps of each tire. good luck , if you are at any of our races look me up . at the ITS #86 rx-7. ralph
 
Thanks for all of the great advice everyone! I believe that I am about to put the car in the garage permanently for the winter and work on some body cosmetics, (new S5 fenders and front bumper) and I will also work on getting a air damn fabricated as well. I might even throw in my good S5 motor out of my parts car that only has 70k miles on it. And if the money is there, I'd like to get my roll cage put in so that I can go to the TT school at TGPR in Feburary.

My only problem is now that I'm out of money!!!

-Vincent.
 
VinnyV81 said:
mbuskuhl said:
Cheapest option - Momo Start $361 shipped, FIA seat

What is the best way to mount the seat Mark?

-Vincent.
Click to expand...

Don't make the mistake I did and buy a bottom mount seat, although I don't think they even make those anymore. I had to have custom brackets made up and used the stock mounting points. Complete PITA.

Get a side mount seat and the brackets like these http://cgi.ebay.com/ebaymotors/MOMO...emQQimsxZ20081123?IMSfp=TL0811231310004r37480

I'd sell you my setup but I'm going to put it in the passenger side and get a Racetech seat soon. If I had it to over again I would have just spent the money and did that the first time. I want a head restraint.

If funds are tight, just get a Kirkey aluminum seat off ebay and put a seat back brace on it. There are plenty of used seats on ebay and you don't have to have FIA.
Click to expand...
 
Also, what size tubing did you go with in the roll cage in your car Mark? I found a local roll cage manufactuer here in Alabama that I am considering getting my tubing pre-bent from and I would like to know what the rules allow for. I have been told that 1 3/4 DOM that is at least .095 thick is needed, but to me that sounds a heavy duty for the vehicle weight according to the GCR.

Thoughts anyone?

I also found a 10 point roll cage kit on eBay from BD Racing but it is EWS and is 1 5/8 and .134" thick. I plan on ordering a kit, and doing the install myself with the help of a welding buddy of mine.

-Vincent.
 
1.75 x .095 DOM

If you get confused on roll cage rules, start a thread and ask but make sure you looked through the GCR first. The rules are specific on some things and you don't want to do it twice.

Honestly, you are probably best finding an SCCA cage builder and letting them build it. You want it to work right if you even end up needing it.

A 10 point cage won't work, even if DOM. Not legal.
 
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