Back End Feels Light

[AMR33]

Hey folks,

I noticed on the track that the back end of my R33 gtst feels a bight 'light'. What I mean by that is that if im coming down the straight doing around 160-170kms the back feels a bit bouncy and unstable. I've added a bit of weigh in the boot which seemed to help a bit.

Any idea what could be causing this? My guess is that my suspension is simply not cutting it on the track. I currently have JIC height adjustable coilovers but will be considering upgrading when I have the money. Other suspension components (arms etc) are also stock. I lowered the car but dont want to go much lower as it seems to be at good height.

If you guys have any thoughts please let me know.

Cheers

Amir

[GTSBoy]

Too stiff.

[warps]

Don't put weight in the back to try to counter bad suspension setup. That's a terrible idea.

Hard to know exactly what is wrong - too many variables. Could be poor alignment (toe), poor damping, slop in bushes, tyres themselves. It could even be the front end causing problems at the back (mismatch, poor alignment etc.)

How do you know it's at a good height? Just from looking at it, or because of the amount of travel (bump and droop) you have available? How has the ride height affected geometry? Are the dampers in good condition? (ie did you buy them second hand?)

Best advice is to take it to a suspension place (preferably one who understands track cars) and check out what you have (bushes, alignment, shock tests etc.). This might give you an insight into what's going on

[AMR33]

Cheers guys. I think it is too stiff. I got alignment done by Wheels World - Peter races in Targa etc and is quite knowlegable. He gave the thumbs up for ride height and tried to do the best allignment with the stock components. I agree that adding weight is silly in this instance but I did it to test for any differences.

I am looking for new coilovers and other suspension bits to allow for adjustments so we'll see what happens. Meanwhile its good to get some input so cheers.

[GTSBoy]

Got any ideas on the spring rates involved? Which track? Is that straight smooth or does it have any low or high frequency bumps in/on it?

Springs and dampers need to be matched to tune them to a particular frequency. Race cars get stiff springs in order to limit body roll and to make one part of the suspension (the springs) suited to high frequency inputs. That's because when going fast the input of bumps and the transitions caused by changing directions are short and sharp. When running stiff springs, the dampers then have to be matched so that the system isn't horribly underdamped at the frequencies likely to be experienced. Horrible overdamping is also to be avoided, but probably not as bad as underdamping. BUT......one thing that can happen and is spectactularly funny to see is when the rebound damping on a suspension is so high relative to the spring rate that the car will jack itself downward whilst driving around. Each bump compresses the spring, but the damper doesn't allow the suspension to re-extend. A mate of mine when I was a kid had a 116 ALFA with Koni Yellows wound to max stiffness (rebound adjustment only on these things) and stock torsion bars and rear springs. It would arrive into the carpark at work at lo-rider height and over a period of 5 minutes would raise itself back up to normal sky high 116 chassis height. It made it an awful harsh billy cart to drive around in. The suspension was too soft everywhere except in rebound damping, and so when it became compressed, it became too hard everywhere, with no bump travel.

Worth considering both aspects of the above with ref your car. Maybe the springs have been changed on those coilovers, either to higher or lower rates, leading to one or the other problem.

Edited October 27, 2014 by GTSBoy

[AMR33]

Cheers for the info mate. The straight Im talking about is quite smooth and doesnt really have bumps - but I seem to feel anything I go over as Im guessing the spring rate is too stiff. I'm not sure what the spring rate is but I can tell you it is very stiff - too stiff. I will look into what you said mate, its great info. I dont think there's much I can do till I get new suspension. Or is there?....

[V28VX37]

Are you still running HICAS? If so, gave you checked your HICAS ball joints? For track use you probably want to ditch HICAS anyway so a lock bar or an eliminator kit might help.

EDIT: Also you might just need more aero. Years ago at Sandown I felt the car getting really light in the rear at the top of hill near the end of the back straight at ~190 clicks, not a nice feeling...

Edited October 27, 2014 by V28VX37

[AMR33]

Are you still running HICAS? If so, gave you checked your HICAS ball joints? For track use you probably want to ditch HICAS anyway so a lock bar or an eliminator kit might help.

EDIT: Also you might just need more aero. Years ago at Sandown I felt the car getting really light in the rear at the top of hill near the end of the back straight at ~190 clicks, not a nice feeling...

no HICAS mate, got the lock bar on. I was also considering aero, maybe a decent rear wing to give it some down force. But for now I think sorting out the suspension is the main priority. And you're right, its not a nice feeling at all. I find myself wanting to come off the gas as Im afraid the rear end will kick out and send me into the wall at 170+ Ks an hour.

Cheers for the input

Amir

[GTSBoy]

Lock bar doesn't prevent the outer tie rod ends from allowing slop. Worth a look. But HICAS problems are more likely to make a car feel left-right unsettled than up-down unsettled. Should be relatively easy to tell the difference at 160+.

[niZmO_Man]

Two Zimbabwe cents on flogged out rear struts.

[AMR33]

Lock bar doesn't prevent the outer tie rod ends from allowing slop. Worth a look. But HICAS problems are more likely to make a car feel left-right unsettled than up-down unsettled. Should be relatively easy to tell the difference at 160+.

Its an up and down rather than side-to-side movement.

Two Zimbabwe cents on flogged out rear struts.

uhhh what now?

[GTSBoy]

Nizmo man made a very small bet that the rear dampers are stuffed. This is certainly a possibility. I didn't go there in initially talking about your problems because I was willing to assume that if you had HSD coilovers then you'd probably know their condition. If that assumption is not valid......

Edited October 28, 2014 by GTSBoy

[AMR33]

I see I see. Yes they could be stuffed. No, Im not 100% sure of condition. Will get in the garage over the next few days to do bits and pieces so will have a look. Anything in particular I should look for? Leaking oil etc?

Cheers

[GTSBoy]

Leaking oil, yes. Dismantle (springs off) and stroke them up and down. Comparing them against each other and any other struts you might have (or other experience).

[AMR33]

Will they get stiffer if I stroke them up and down? Thanks for the help mate. Will have a look at them soon and see where to go from there.

[Ben C34]

Will it get stiffer if you stroke it?

Hmm.

[GTSBoy]

Thread derailed. Again.

[SkudR33]

Will they get stiffer if I stroke them up and down? Thanks for the help mate. Will have a look at them soon and see where to go from there.

Hahaha definite derail!

[AMR33]

ahahahah yeah I had to

[niZmO_Man]

Bahahaha.

Man, you said you have old JIC coilovers. They are usually pretty stiff (running 8+ kg/mm spring rates), so they may be what GTSBoy said in post #2. Coupled that with old, worn dampers, you'd get that bouncy feeling.

Get some MCA suspension .