Suspension Settings, Hicas Or Bushes?

[jjman]

So on the weekend i was doing some driving (track) at a speed id not done before and had some ass clenching 'feedback'.

Basically i was doing about 170km/h and turned in to a fast left hand curve at 170km/h and while i could feel i would be close to the limits of my mechanical grip i was nonetheless within it. But the car handling feedback i got was not a good one.

Essentially the turn in was perfect (no understeer and it pointed very well and communicatively) but after that the tail end started doing this strange swaying (3 sways: first into oversteer, then under then over) that was a bit too much movement for my likeing at that kind of speed. I had to correct the sways with steering inputs otherwise im sure it would have meant a spin (crash).

A point worth noting is that the tyres were not breaking traction, it was just that the rear end was swaying.

So my question is, what is most likely to have caused this?

The HICAS? the limits of the car and my suspension, tyres etc? old bushes that might need replacing?

as a bit of a run-down i have

An R33 GTS-T

275/35/18 toyo proxes on the rear.

GTR sway bars.

BC coilovers 8/6kg springs (mid damping on the front and lowest on the rear) Car lowered considerably.

HICAS is still on the car...

Other factors-

road surface was very good and grippy- though it was fairly low ambient temp and my tyres werent exactly really warm either.

Anybody familiar with the characteristics of GTST's in this kind of setting and what might have caused this?

cheers

J

[jrm]

HICAS does not operate >110kph.

[simpletool]

Understeer, then traction, then oversteer again? Or rear swapping sides?

How quickly did the transformation take? less than 1 second or several seconds?

Wheel to guard heights?

Have you check the rear end for play?

Edited August 29, 2011 by simpletool

[jjman]

ah interesting, i did not know that about HICAS not operating above 110. That rules that out then (unless there is freeplay in the HICAS mechanism...)

Understeer, then traction, then oversteer again? Or rear swapping sides?

How quickly did the transformation take? less than 1 second or several seconds?

Wheel to guard heights?

Have you check the rear end for play?

transformation was very quick. N it was more the end swapping sides (tho not breaking traction) n it swayed into essentially oversteer first n then swayed the other way, then the other again n then settled drown.

It might have been that i did turn in quite aggressively n it just meant that the rear weight transfer just flicked the back a bit which then took a couple of sways+corrections to settle down.

wheel to guard is about 1-2cm. see attached pic (tho in reality it sits a little lower than this in the rear as it is on the back of a flat top tow in that pic n on the angle with the handbrake on means the rear is sitting about 1-2 cm higher)

I havent had the rear end checked for play recently (did about 9 months ago n all good). Have also had a full 4 wheel alignment about 6 months ago.

Prob will check for freeplay again n get into a suspension shop for a comprehensive look-over.

Can the HICAS systems get freeplay in them or do they lock well when that get above that 110km/h threshold n turn off?

[jrm]

ah interesting, i did not know that about HICAS not operating above 110. That rules that out then (unless there is freeplay in the HICAS mechanism...)

Can the HICAS systems get freeplay in them or do they lock well when that get above that 110km/h threshold n turn off?

My HICAS stuffed up for a while, and I pulled the fuse for it to limp it by for a while. That 'while' turned into about 6 months. After 6-months I got my steering-angle sensor sorted, but the HICAS rack had had been uncontrolled from the fuse being pulled during that time that it had developed excessive free-play in the rack itself. I had to replace the rack with one without play to fix it once and for all. So yes, they can wear, and they can get free-play in the rack itself.

I learnt about the 110kph turn-off in an interesting way. When my HICAS steering sensor was mis-aligned, the car would progressively steer my rear wheels sideways (causing the car to crab) and the steering wheel to 'turn over' to compensate from about 60kph onwards. The first time I got onto the highway and hit 110kph, the car & wheel snapped straight as the HICAS disengaged, nearly caused an accident (which is why I quickly pulled over, and pulled the fuse, as I was driving from Adelaide to Melbourne that day).

I'm not sure how the HICAS system turns off at 110kph - I would assume it would have to lock the rear-tyres in the straight-ahead position. However if the rack has any wear & play in it - obviously this could cause handling issues.

[jjman]

mad. that cant have been fun...

[boostn0199]

Just f**k it off if your going to track it. Also if your tracking change all the bushes in your suspension. 15 years there gona be pretty average if not completely dead also the control arm ball joints will be gone.

Dont know how serious you are about the car at the track but i would just adjustable arms and do the bushes and get a good grip alignment.

[simpletool]

Could be a few things but sounds like play somewhere in the rear end. There is a lot of bushes that need to be replaced. Do them all at once.

You didn't mention if you had pinapples installed (subframe urethane lock). This would be a good first start.

[jjman]

Could be a few things but sounds like play somewhere in the rear end. There is a lot of bushes that need to be replaced. Do them all at once.

You didn't mention if you had pinapples installed (subframe urethane lock). This would be a good first start.

no i dont but the pineapples are the next mod that is going in- just after the camber arms so i can have it all aligned at once after this n will get them to have a look at the bushes just prior to this.

Hey, im still trying to get some more seasoned advice on the pineapple issue. I plan to put in pineapples that help 'grip', particularly in take-off and straight line power-down grip. How truly effective are they at this beyond actually getting the camber just right in the first place?

and, most importantly, are the any compromises that this sort of pineapple introduces?- such as reduced lateral (cornering) grip?

cheers

[simpletool]

I'm no expert and it's been awhile but I think the general recommendation is maximum stability - which is FLAT. (neither grip or slip)

Edited August 31, 2011 by simpletool

[jjman]

yeah right. Cos the reputable garage im speaking to says put in the traction pineapples that tilt the subframe a certain direction which = more grip.

But.

1: usually with anything there is a tradeoff otherwise the factor would have done it like that or everybody would do it aftermarket

2: a garage has the agenda to sell me something and make a profit so its not unbiased...

[GTSBoy]

Pineapples are a good idea. You can put them in 3 ways. 1 enhances longitudinal traction but negatively affects lateral traction, one is neutral and one enhances lateral traction but negatively affects longitudinal grip. If you are worried about losing grip in either direction you just put them in neutral. Regardless of this, they certainly help to lock the subframe up a bit tighter to stop it steering the rear of the car.

Even better is to buy a full set of Whiteline subframe bushes and replace the 15-20 year old ones.

If I were diagnosing your problem I'd suggest that bushes could be worn, HICAS tie rod ends could be worn, subframe bushes could be sloppy, but the HICAS rack itself could be to blame. The electric ones sometimes seem to have some random behaviours. (So do the hydraulic ones - but I know what they do - I have one and I'm getting rid of it, and the entire HICAS subframe).

[jjman]

hmmm, yes well this confirms what i thought... would have to rob from peter to give to paul.

I might just see what putting in the camber arms can do for me.

On that note, does anybody know what is the best camber for the balance between longitudinal traction and lateral traction? At the moment im at 1.2 degrees from memory which is as straight as i can get it at my current ride height on stock R33 camber arms. Iv heard .5 degree is about best...?

As far as all the bushes n freeplay goes im hoping its not to bad. iv never had any symptoms of anything prior to this n this was a pretty extreme setting so for normal to even spirited driving i think everything might still be working well enough.

N its not that i wouldnt want to get it done if it needs but a modified R33 is always crying out in numerous ways for $, time and attention right?

which means it becomes a priotity list depending on the need at any given time...

n the current top of the list is the camber arms, and fitting the fresh HKS turbo iv got sitting there waiting for action (stock turbo @15psi is screeching real bad) and doing all the exhaust manifold bolts n gaskets.

Cheers again for the thoughts n advice people.

Edited September 1, 2011 by jjman