240Z Autocross Suspension Setups (all-out)

[zredbaron]

I'm feeling a bit overwhelmed and turned around and I don't know which way is up anymore...

 

I read the sticky regarding camber plates, and all I got out of it was a bunch of arguments about different designs, and came out more confused than I started. Sweet.

 

I also re-read a thread I posted long ago regarding spring rates ( http://forums.hybridz.org/showthread.php?t=88512 ). The thread basically says for me to keep my spring rates light, not really to exceed 250-300, both because I have Illuminas and because I have a non-reinforced 240Z frame.

 

My '71 240Z is finally a garage and enclosed trailer queen, and I'm finally taking it to autocross events on the weekends. I've only done about 8 events (ever) and I'm at the point now where I need to dial in my suspension. My setup is rather simple at the moment, 225f/200r coilovers with Illuminas. 1" front sway with 3/4" rear. I have no camber or caster adjustment yet.

 

But at my local SCCA region (Oklahoma) they aren't even close to the recommendations found here at HybridZ. There is an autocross 240Z, non-welded, and he runs 400lb springs in his illuminas. He has minor camber adjustment. He runs in BSP (my car is technically FP but I run in SM2 because I'm not gonna win at this point anyway) and puts down 3 sec faster lap times. Granted, he has slicks and is a much more experienced driver, but still. He isn't remotely close to the power and accelleration I have. He has 400lb springs in front and ~250 in rear. All the hybrid Z guys say to run stiffer in rear. He contradicts this and drives really, really smooth like this.

 

Theres a road racer / autocross 240Z (SM2), with welded frame, that runs 600lbs front and i think 400 rear), again stiffer in front. Also with Illuminas, oddly. Also very successful.

 

I took a ride in a mid-80s bmw 325 with the EXACT same tires (model and size) I have, and I can't laterally hold what he can. He runs 600 up front and under 300 rear.

 

Reading posts from John Coffey and a few others, these spring rates are absolutely ridiculous and the car should be bouncing.

 

So you see my confusion. I trust the hybrid z forum, but i'm also experiencing successful contradiction first-hand.

 

I know that camber (and caster) is huge, and I'm looking into it for my Z. As usual, I want the best, damn the cost, but I don't want to invade my frame. My 240Z racer also happens to be in pristine condition inside and out and I am not willing to cut it. I want the car built for all-out autocross (FP), I don't care how undriveable it will be on the street. I'm not willing to put reinforcement bars in, so if that restricts me to <300lb, so be it. The best I've got is triangular strut braces, front and rear.

 

So what is the ideal? How should I change my spring rates, and what should I do about camber/caster? The EMI plates look awesome, but so do these http://www.technotoytuning.com/products/camber_plates.html, mentioned from the camber sticky. No one has reported actually using them yet. Again, for the ideal setup, am I correct that this would also include adjustable front control arms and tension compressin rods? (Or would having one negate the need for the other?)

 

Also, I seem to remember John Coffey telling me that because I have a Quaiffe, running without a rear sway bar, although it feels weird, will improve lap times by letting it squat that torque in around those tight turns. Any comments on that?

 

Thanks again, guys. I look forward to learning from all the experience out there...

 

-Mark

[zguitar71]

If you are not going to cut up the car then you will have to use the wheel/tire set up I have in FP. I use Goodyear G-19 23x9x15 R250 tires with 15x7 wheels with a -12 offset. They do not rub inside or out though they do stick out past the fender but they are so small in diameter they do not hit the fenders. I have AZC springs 200 rear and 180 front with Illumina's. I have 4 1st place finishes this year and 1 2nd place out of 5 races (so far) against other similar z's, 911's and 914 6's with better set ups, same tires. I have about -1.75 camber in the front with 1/4 of toe out and -1.5 camber rear with 1/4 toe in. I got that from using camber bushings. The caster is whatever it came with from the factory. My car has the poormans set up and I win often including 3 fast times of the day trophies so far this year. It is not what you drive but how you drive it. Your car is set up just fine like it is except I would move the stiffer springs to the rear. If you go stiffer than 250 springs with the sticky tires you will run the risk of cracking the body of the car because you do not have any reinforcements. I don't have reinforcement (except strut bars front and rear) in my car and no problems yet but I bet I will at some point, the super sticky slicks are hard on the car's body (flex). I have seen many cars with 350-400 springs on the Illumina's and they do handel well. I have heard the heavy springs will over work thus over heat the shocks and run them eventually. Autocrossing probably does not generate the heat due to the short run time; though, shocks valved to run heavy springs (400 or so) probably do handel better.

 

Ground Control makes some camber plates that do not require cutting the tower tops and the EMI plates do not require cutting either. The difference between my car with good street tires and slicks is around 6-11 seconds depending on the course. If you go to the slicks I use you should gain more than 3 seconds. The Quaife requires the unloaded (inside)wheel to have some traction in order to throw torque to the outside (loaded) wheel. The softer rear, no sway bar in the rear, set up allows the inside wheel to stay on the ground harder giving more traction to it thus getting more torque to the ouside wheel.

 

If you are not willing to cut, cage/reinforce, strip and flare the car then you will never be to the potential of FP. A real FP car is not streetable. They weigh 2100 LBS (with a 2.8) and have 300+ HP and high compression requiring race fuel with a big cam, ect... No modded up street car with a set of slicks slapped on will compete, though they do a pretty good job. In a real FP Z I will always out run my car, just how it is. I say get some slicks and have fun and remember your driving abilities dictate the time more than the set up. When you are driving really well then your times will get better with the better set up.

[JMortensen]

If you want all out, go all out. If you don't want all out, don't run FP (and expect to win anyway).

 

Lots of people run Illuminas with extremely high spring rates. All that this proves is that you can put a 600 lb spring over an Illumina strut, it doesn't mean that it works well. It also doesn't mean that those people won't be faster than you. As discussed in the calling all racers thread it takes a lot of effort to even know if one shock is better than another, let alone to know if the shock matches the spring rate.

 

Forget comparing the BMW rates to your Z. They have semi-trailing arm rear suspension and what they're doing doesn't translate well to what you're doing. The numbers that you quote don't sound right though, because the semi-trailing arm rear suspension has a leverage ratio of something like 3:1 so the 300 lb rear springs would be the equivalent of a 100 lb spring on a Z which has a .98:1 leverage ratio.

 

I'm really surprised to hear about the one guy with the 600 lb springs in front and 400 in back. I suppose it would depend on what else he has on the car, but my problem has always been to get the front end to stick, and I never had too much trouble with the back end. In fact, this ties into the Quaife comment too. The Quaife is just not a good autox diff IMHO. You tell me if your experience is different than mine, but mine up to this point has been a struggle to get enough camber and caster to keep the front end planted. If that's the case with yours then it helps to have the rear end stiff to get the car back to rotate instead of understeering all over the place, and that as John says is what the Quaife doesn't like. If you could really get the front end dialed in, then maybe softening up the rear might be an option. But as long as the you've got understeer, harder front springs and no rear bar is a no-no IME. A roadrace setup is totally different and doesn't require the instant turn in and rotation that an autox setup requires IME.

 

tube80z is a fan of the really high spring rates and runs with a lot of Z's that are over 400 on various strut combos with various states of chassis stiffening too. Hopefully he'll chime in, but what he has said to me in the past is that chassis stiffening is VERY important. I think I might go down the path of running insanely stiff springs too after talking to him about it quite a bit, and I've been trying to stiffen the chassis for just that reason. I won't do it until I have struts that can handle the spring rates.

[zredbaron]

I didn't think of the possibility of leverage ratios being different...that makes so much more sense now for the bmw's 600 lb rate. The 300 rear is probably wrong.

 

I just looked at SCCA's rules for the different autoX classes, and I don't know why I thought I wasn't qualified for SM2...it looks like I'm okay for that category, which is awesome news considering I won't cut my car or stiffen it and of course would like to still have half a chance someday when I get some experience under my belt.

 

So. Thanks for sharing all of your experiences. I'll have to experiment with the rear stiffness once I get some camber adjustment going for me. At the moment, I push quite a bit on the tight 180 degree turns, but do well (neutral) on sweepers and slaloms.

 

If anyone else out there has any more to add, I'd love to hear what you have to say. I'm feeling like a sponge at the moment...

[tube80z]

Hi Mark,

 

Here's an old thread with some info that may help you. One big item to think

about is tires, will you run slicks in prepared or a street radial for SM. That will make a difference in picking rates to go with.

 

For let's start from the beginning:

4) car set-up as per John Coffey:

Camber - 3 degrees neg front and 2.5 neg rear (fine tune with pyrometer). Some tires need more insided temp to work correctly but in general will be 10 to 15 higher (slicks) and may be even higher for radials.

 

Caster - 6-8 in front (you can decrease camber if you have more caster)

General rule of thumb is one half KPI (steering axis inclination). When running this much caster you also need to check to make sure you don't have too much caster trail (mechanical trail). You'd like to have around half an inch.

 

Also try to have no more than 20 percent of tread width as scrub.

Toe - 1/4 to 3/8 out in front and 1/16 to 1/8 in in the rear

For tight track try rear toe out.

 

Ride Height - 4.5 to 5 inches at the rocker (don't try to over lower the car)

Springs - 400 all the way around (ideally should be set based on scale weights and multiplier for tire type -- perhaps another discussion). You'll need proper shocks to make this work. Helps to quicken transition times and keep suspension geometry for going all over the place.

 

Sway bars - 15/16 to 1-inch front and 5/8-3/4 rear -- both need to be adjustable and connect to the strut, not the control arm. Sway bar should be in a low friction mount, which is not poly or other form of pinch block. Ideally at least one is driver adjustable for when you need to make the last minute tweak between runs. See what Jon has been doing for an idea of a low friction mount.

 

Offset bushing - yes

Will be needed for street prepared but should be avoided in other classes.

 

Never use Poly suspension bishings, it has too much friction. These need to be low friction pieces to help with mechanical grip.

 

Good advice on notes deleted(lookup the original thread). A tire pyrometer is good to indicate wear but not a lot more. But tire pressures are more accurate on how the tires are used. You should work on a setup that gives you an even rise in pressures. This is where good notes and understanding what you need for a hot tire pressure is important. You can switch to nitrogen to help eliminate the effects of water vapor in the tires.

 

To adjust chassis balance you can change the rake. Rule of thumb is two turns of the spring collar to start. If the effect is too much try one turn. You lower the end that isn't sticking. Make sure you keep the arms near lever and don't end up too low. The car should be corner weighted. Make the front level and the front weights as close as you can and live with what you get in the rear. Move as much weight down and towards the back as you can but not behind the rear wheels.

 

Remember you need to make ride height changes to compensate for weather conditions to keep a balanced chassis.

Also consider using shims for camber/caster plate alignment. These allow rapid known changes and/or allow you to get the car put back together without having to do a major alignment.

 

Before an event always know all your settings. Keep notes of any changes that you make at an event. And at the end of an event do a setdown. This last step is important and few people do it.

 

If you're using the same size tires all around keep notes on how hard they were used and rotate to keep the use as close to the same as you can. Do all chassis setup work on old tires (but not junk). New tires will mask a lot of the changes until you have killed them. By doing all this you'll end up having a car that is kinder to its tires.

 

A number of assumptions have been left out of this thread, like bumpsteer, corner weighting, checking for compliance, suspension binding, etc.

 

Test, test, test, and have lots of fun.

 

Hope this helps,

Cary

[Dragonfly]

But at my local SCCA region (Oklahoma) they aren't even close to the recommendations found here at HybridZ. There is an autocross 240Z' date=' non-welded, and he runs 400lb springs in his illuminas. He has minor camber adjustment. He runs in BSP (my car is technically FP but I run in SM2 because I'm not gonna win at this point anyway) and puts down 3 sec faster lap times. Granted, he has slicks and is a much more experienced driver, but still. He isn't remotely close to the power and accelleration I have. He has 400lb springs in front and ~250 in rear. All the hybrid Z guys say to run stiffer in rear. He contradicts this and drives really, really smooth like this.

 

Theres a road racer / autocross 240Z (SM2), with welded frame, that runs 600lbs front and i think 400 rear), again stiffer in front. Also with Illuminas, oddly. Also very successful.

 

[/quote']

 

Two words for you "seat time". Up to a point the person with the most seat time will run better times even if thier setup is not what it should be. Take the advice of the guys on here with plenty of seat time and good setups and you will find that your times will improve, and you will soon be beating the cars that are not set up as well. Practice, practice, practice.

 

Dragonfly

[OlderThanMe]

great thread! My setup is: Illuminas, 225lb/in front, 250lb/in rear. No rear swaybar (removed) and stock front (unfortunately). I am also running poly bushings (the rear control arms were fun to install with the new bushings! lol). I had my front struts on 4 and the rears on 3 thinking that since the front was harder it would grab sooner. haha... I would understeerlike crazy!!! I then swapped the font to 3 and the rears to 4 and it is VERY neutral! I still have to finish my suspesion off with weld in camber plates, bigger sway bars, strut bars...

 

I don't see how that 240Z could be good handling with a difference of spring rates front to back. 400 front, 250 rear sounds like a lot. I guess it depends onthe settings the car has though. I was going to do my first autox event this summer but my engine decided it had enough already.

[zredbaron]

Wow, TONS of info on this thread. Awesome.

 

I'm definitely confident again that my 225/200 springs are in the ballpark, and now I have camber numbers to try out once I get the capability. Thank you all so much!

 

Never use Poly suspension bushings, it has too much friction. These need to be low friction pieces to help with mechanical grip.

 

This is the first time I've ever heard anything like this. Years ago I replaced all my squishy stock bushings with polyurethane...and now you're saying that I should have something else. What whould a low friction piece be made of? Do you have a picture or a link of one?

 

About the seat time, I am fully aware at how inexperienced I am, especially out there on the track. I'm not an idiot, and I don't expect to win anytime soon. I do however want to do as much as I can with my suspension, so that I can learn to drive the car as it will be one day when I know what I'm doing.

 

Another side note on experience...I am limitiing myself to do my first 1-3 seasons (depends on how long it takes me to come around) on street tires (Kuhmo Ecsta MX), so that I'll pay for my mistakes. With my power/drive ratio combination and my brakes, it's really hard to drive smooth as an rookie. Not to mention the car's technology is older than I am, haha. Damn, it's fun though. The theory is, if I can get fast on street tires, I'll be on rails with DOT slicks.

[JMortensen]

Low friction means not poly bushings. Other types of bushings are better like the G Machine bushings, but really low friction means usually means monoballs/rod ends/heims joints. I started out my rebuild planning to use poly in the rear and poly on the sway bars, but Cary kept mentioning how bad it was. I really didn't know what he was talking about until I started to mock up my rear suspension to check for bind. I was using poly rear control arm bushings, and just had the strut assembled and the spindle pins through the control arms but with no nuts on the end of the pin, and also did not have the big 24mm bolts at the end of the control arms tightened down. When the nuts on the spindle pin and the bolts in the control arms get tightened, it compresses the bushings and dramatically increases the stiction. Even with it loosely attached like I had it the stiction was not good. I can only imagine that with everything really tightened up it would probably take 75 lbs of pressure on the outside of the control arm just to break the bushings loose and get the arm to move. Imagine when you loosen a lug nut and you push and push and push then it suddenly breaks free and starts to move. Same sort of deal. This made me want to do something else, and heims joints look to be the answer. I'm still working it out, but you can follow this thread to see where I'm at: http://forums.hybridz.org/showthread.php?t=106457 I did get the swaybars done as Cary said and I think that will help A LOT too. Here is the swaybar thread: http://forums.hybridz.org/showthread.php?t=105596

 

The front end of my car is all heims joints with the exception of the inner tie rod and the ball joint, and it's amazing how freely the suspension moves up front. Contrast that to the back, and it was easy to see that something needed to be done back there.

 

This is a "how fast do you want to spend" thing, so if you decide to go all heims joints, the joints themselves are expensive, and then all the fabrication to get them in isn't cheap either. Doing it myself I probably saved a bunch of money, but I still have many many hours out in the garage redoing the sway bar stuff until it worked without binding (took me 3 or 4 attempts front and rear) and then there is the cost of the tools and all the materials, etc. Mine isn't going to be a practical street car when its done, so you have to ask yourself how far you want to go. Is it a race car or a street car? Heims joints don't last forever like poly bushings, and they don't dampen noise or impacts either.

[heavy85]

Lots of good advice up here that you should take in and apply, but also consider you can make up three seconds just by switching to race tires from street tires. Tires make a HUGE difference.

 

Cameron

[johnc]

Autocross cars can be effective with a suspension setup that has very little suspension travel. 2" of total wheel travel can work if the course is fairly smooth and you run a lot of spring. In those cases on a 240Z, the chassis itself is acting as an additional spring (like a shifter kart), which can work but is more difficult to tune. Cars like that are very difficult to drive quickly but a lot of seat time can get a person used to a particular setup and be fast with it.

 

What you see recommended here is usually based on not using the chassis as a spring. It makes suspension tuning easier and more effective.

 

BTW... "typical" street prepared E36 BMW spring rates are 700 to 900 front and 500 to 700 rear.

[zredbaron]

Autocross cars can be effective with a suspension setup that has very little suspension travel. 2" of total wheel travel can work if the course is fairly smooth and you run a lot of spring.

 

What do you mean by total wheel travel? Are you talking about vertically? (That seems like a lot in a racing environment...)

[johnc]

Total wheel travel is bump and droop. Also, Mark, your sig is getting pretty big.