S13 Chassis oversteer a lot on entries

[Croustibat]

Hi guys, i am new here, although i have been reading around for some years now. I am french, so please tell me if i offend you in any way.

I own a european 200sx S13, which is the 240sx s13 you know with a CA18DET in it. I modified it some, basically i have stock internals with a GT2560R turbo and all supporting mods. Also running e85 fuel with octane >100, which helps a lot, and tuning all of that with a nistune board. When run at 1.2bar, it is around the 300whp mark. Never dynoed thought, i am not interested in the hp comparison. I am using powerdyn to check mods, so far it has been quite useful.

My current problem is not engine related though. The chassis has also been quite modified, and i use the car as a trackday one. Rules & regulations in France are quite harsh and my setup is completely illegal for road use (any mod here makes the car illegal anyway), but i dont care, it only sees the road when going to a track. So far i have been driving for 15 years and never had an accident, hope it continues.

I am currently having a big chassis headache. About a couple month ago, i did some major work on my S13 chassis, and since then the car "overturns". Corner entry is terrible, it feels like the car has rear wheel steering, and some other people told me it felt like that too.

Steering response feels just like an integra type R, with its torsen on the front wheel drive pulling in the corners. It is somewhat fun, but i do want to tell my car where to go, and not preventing the steering wheel from turning on its own once i start turning it.

Once entry is done, mid corner and exit is fine, it understeers a bit on exit and that is fine with me.


Here is the chassis setting and mods:

half rear rollcage
strut braces F/R
apex gen2 5/4 coilovers, fronts modded to let the tyre pass (the higher hole used to bolt on the spindle was ovalized, so i could incline it a little bit more. Not a lot, maybe 3mm)
godspeed ARBs front and rear
complete apex alignment kit front and rear
new steering rack arms with bump steer correction
S14 front lower arms ( 8mm wider than S13 each) - i went 5 studs
polybushed everywhere spindles, arms, engine, gearbox, rear subframe
8mm plates between chassis and front subframe anchors, to tilt it a bit (to remove some antisquat)
wheels have maxxis MAZ1 235/40/17 on them. specs are 17x8 front ET 35, 17x8 rear ET38.

Car is sitting level, as high as apex 5/4 coilies will allow without putting a lot of preload on the springs (there is 5mm preload on each). This is about 19cm above the road measured from ground to sils.

Settings are 7° caster, total 5minutes toe out front, 6 minutes toe in rear, -1°30" camber front, -1°camber rear


Last time i tested on a track, i just needed to turn a bit and immediately counter steer to prevent the car from spinning out. Obviously this is not good at all for grip driving ... It really felt the rear suspension is toeing out dynamically and turning.

A couple of friends helped, and we closed rear hydraulics, as it turns out it was way too soft. This made the problem happen later and only on harder corners, but still it was better, and i enjoyed my day. It did confort us in the idea the rear is toeing out on load.

I just dont understand how the car could change like that. The last job done on the car consisted in fitting the wheels, rear subframe polybush and antisquat mod, and the car did handle "well" before (it understeered a lot but was quite predictable), so i guess it has something to do with either :

-larger track width at the front
-antisquat mod
-coilover mod

my bet is on the first, really. I happened to do the front 5 studs mod and got tired of that, so brought the car to my mechanic to do the rear. Now i know it was toeing out badly at that time, but the car felt the same, although at a much slower pace (i was quite scared and drove slowly) . But i thought it was just a geometry problem, and that it would be sorted.

I also noted after my trackday testing that my front tyres showed signs of gum ripping away, but not the rear ones. I was running only 0.9bar boost (stage3 + e85) as it was very hot and i wanted to test the car, not crash it.

Basically, the question is "what is wrong, and what can i do to solve that ?"

Is it just the larger front track width ? If it is, i could solve it with a pair of spacers. Is it because the front is set to toe out a little ? Did i completely mess my rear train by tilting the subframe ?

I started to take some measurements too, and i could see that the rear traction arm from apex is longer than OEM one, even on its shorter setting. Could this be the cause of my problem ? I still have the oem one, but it has an old bushing in it...


If someone had the same problem, i would be glad to hear from him/her.

thanks guys (and girls but i fear they are not a lot here )


note : sorry for writing too much :blah:

i posted a similar thread on sxoc, but people there are not very fond of gripping.

[Croustibat]

So, 50 viewers and no answer.

No one here tilted his S13 subframe or used S14 front lower arms ?

[PoorMans180SX]

I would add negative camber in the front, something like 2.5* and change your toe to zero all the way around. Toe has a surprisingly large affect on turn-in.

Your traction rod should be about 8.5 inches long for ideal toe curves in the rear.

Them make sure everything is good and tight and there is no play in your steering rack or subframe.

Hope that helps.

[Silverbullet]

Once entry is done, mid corner and exit is fine, it understeers a bit on exit and that is fine with me.

... so i guess it has something to do with either :

-larger track width at the front
-antisquat mod
-coilover mod


A longer front track would allow steady state over steer so its something you would feel in mid corner also if you barely touch the gas.

Corner entry over/understeer can be associated with the toe like Poorman suggested, but also try softening the shock damping stiffness (hydrolics as you refered to them as) in the rear. They affect transient response which is most felt on corner entry.

[Croustibat]

Thanks guys.

My rear traction arms are 22cm (2/10 more than 8.5") from hole center to hole center currently, i will check again and try to shorten it, if i can.

I tried different toe settings before, the car typically acts like both front and rear are toeing out. But 5 and 6 minutes total are not a lot. i will try adding some toe in to the front, but am not very keen on adding toe out at the rear, as it should amplify the problem.

Damping wise, i have no separate bump/rebound setting, apex coilovers are the same as BCracing ones. The harder I set the damping, the better the car drove, problem was getting way out of hand when soft so we all thought the rear suspension was toeing out dynamically. I fail to see why, as it is designed to toe IN dynamically, not out... I will try to compress and film the suspension at the same time.

No trackday scheduled in august, so i have some time to solve that while spending the less possible money.

I usually only do 1 mod at a time, it is a slow but sure way to go. This is what happens when going too fast...

As of now, i plan to :
1/check if the car has play in the subframe or really toes out dynamically
2/remove the subframe spacers
3/refit them and add spacers to the rear wheels(i can get 3, 5 and 25mm spacers to try)
4/remove subframe spacers and fit rear wheel spacers
5/shorten rear traction arms

If everything fails, i'll get a new alignment done with 0 toe front, a bit more camber and more toe in rear.

I will post progress here, if that can be of any interest ?

See you all :hsdance:

[PoorMans180SX]

Yeah please do, this has me curious.

I don't think wheel spacers are going to do too much.

You can also set the car on the ground and jack up one wheel to see how it moves under suspension compression.

I really think you should set your rear toe to zero.

[gripster]

Remove front subframe spacers (your anti-squat mod)

0 degrees toe front, 1/16 degree toe-in for rear.

I hear you, I prefer grip driving. My car is surprisingly pretty neutral lapping around Laguna Seca.

[Croustibat]

Some news. I had little time this week end, GF was angry because i spend too much time without her, so could not work on the car on saturday.

On sunday, i jacked it up and used a second jack to go from fully extended to fully compressed damper. I learned some interesting things...

1/ i only get around 0.8" of travel in compression ... i guess that really is not enough. How can i fix this ? I have a lot more rebound travel available. I did add some preload on the springs ... could it be the cause ? they are low priced coilovers

2/ the rear wheels rotate (clockwise for left hand wheel watched from left side, anticlockwise for the right wheel watched from right side) and travel "backward" when suspension compresses ! How can that happen ? I dont think it is supposed to happen at all... traction arm too long would cause that to happen i guess ?