Suspension Issues

[tacker]

Guys have a look at the picture and for gods sake tell me what i have to do to correct it!

GT2 porsche spanked me this weekend and not happy about it! The pic is on a banked corner but car is very happy to understeer it way around the entire circuit these days.

[MrStabby]

Have you read through the Suspension/handling Articles sticky?

From http://www.wtrscca.org/tech.htm

"For Steady state understeer, All turns or low-speed turns only;

If front tire temps are optimum and rears are low, stiffen rear antiroll bar; if front temps are too hot, soften front (most likely).

If front tire pressures are optimum, decrease rear tire pressure. Increase if chunking occurs.

Improper front camber.

Too much body roll at front, causing excessive camber change.

For Steady state understeer, High-speed turns only

If front tire temps are OK, increase front downforce.

If front tire temps are too hot, reduce rear downforce."

etc.

[padey]

Guys have a look at the picture and for gods sake tell me what i have to do to correct it!

GT2 porsche spanked me this weekend and not happy about it! The pic is on a banked corner but car is very happy to understeer it way around the entire circuit these days.

Close the petrol cap??

[tacker]

Close the petrol cap??

yep thanks for that

[Sydneykid]

Hi Guys

Can I start by asking what suspension mods and wheel alignment settings you have before we try to fix something. Also, spring rates and tyres (look like a full slick)?

The first thing I see in the picture is body roll in the back - on full slicks, 24mm front, 26mm rear bars would be optimum with sperical links.

Hicas locked?

The rear looks unhappy to follow, possibly due to the load on the outside tyres, but it looks like a pig to drive..

If understeer is the issue, how much camber and caster are you running?

I need more feedback on the overall feeling (corner by corner) before I can comment much more. We need to identify what is wrong before we can fix it.

Then you can go out and give the GT2 back its just desserts!

Cheers

Matt

(Son of SK)

[tacker]

Hello Matt,

mate glad to have some help on the issue i can tell you.

Your correct the picture is on full slicks, but the purpose of the pic was to give you guys an idea of what it taken place.

We now have to run on RE55's which have only seen the issue get much worse as you would expect. The car still feels the same but understeers worse than when the slicks were used.

The set up of the car is as follows

Front ride height 350mm front wheel centre to guard lip

rear ride height 340mm

And we do run with a lock bar.

Front settings

2mm total toe out

3.5 degree neg chamber Cusco items

5 deree castor adjustable rods

spring rate is 10kg

Tein circuit masters on softest setting currently

cusco 26mm front sway bar as white item has not arrived yet but on order.

Rear settings

2mm toe in But i wonder if the car is getting bump steer with the lock bar as it sits with about 5 to 6 degree angle up when on a flat surface.

1.5 degree neg chamber

Tein circuit master on softest setting

Spring rate is 10kg

white line adjustable sway bar on soft setting

Aluminium sub frame bushes in rear.

The car its self is predictable in just about any corner, it will turn in well enough but then goes to quite bad understeer during mid corner to the point its a case of slowing entry speed by one gear on what i used to be able too so i can even get close to the apex. Slow corners i can hold my own but fast to medium corners the car happily understeers through them.

After apex the car continues to understeer through the corner exit unless i wait before starting to accelerate out of corner. It is very rarely that over steer ever takes place and that would be caused by just a little to much entry speed. As i said the car will start to turn in but goes pear shaped after that.

Not the greatest driver in the world but not to bad either ( won national kart titles ) so i could be part of the problem but try to be as consistant as possible when driving.

[Sydneykid]

Hey mate,

As a fellow former karter (who didn't even win a state title, let alone a national), I think we can get this thing handling a lot better. I'm of the opinion you have enough skill to drive the car...

I can identify a couple of issues myself which I think explain the handling woes, without touching on the geometry settings too much (not my area just yet, still in training there)

On full slicks, a 10kg front spring is probably OK. Infact, its probably close to being about right.

However, on a semi slick radial, its waaaay too stiff. You will never get away with using the same spring rates for slicks as you will with a semi slick. . Something around the 6kg mark would be my max on RE55s on a circuit GTR, no more.

I imagine with the shocks and springs used, if you wind up the shock valving UP stiffer, the problem is amplified, is it not?

If this is the case, having an adjustable shock is not doing the job, because you have nowhere to adjust them too. You really need to get a better shock valving, and a good non-adjustable monotube matched with a more suitable spring rate will improve your handling dramatically (there's more required at the same time to improve it, but this is a big start) and probably cheaper than another set of adjustable japaense shocks that will again have the same issues as the current ones.

No upgraded front sway bar - that's one problem.

HOWEVER - if you put the 26mm sway bar on, with the current shock spring arrangement, it will make the handling worse, and will BADLY increase the understeer.

26mm front is, in my opinion, too big. On semi slicks, we tend to run 5-6kg front springs with a 22-24mm adjustable front sway bar. I dare say 26mm will be oversized, especiially if it is bigger than the rear sway bar (whiteline go to 24mm, no larger, and rear needs to be bigger). With a 26mm front, you'd need a 30mm bar on the back - and that's just stoopid!!

Either way, you will also benefit from sperical swaybar links.

The same applies for the rear as the front in terms of shocks and springs

No adjustment there, too stiff in the spring, etc. If it wasn't understeering so badly, it would be oversteering so badly.

The rear sway needs to be atleast 24mm, if not 26mm, with a 24mm front bar.

As a former karter myself, I have NO IDEA how you put up with that much understeer - drives me NUTS!!

There's more, but this is a start.

I need to do more reading of dad's books and notes, not to mention question him, before I get to the geometry, so I'll leave that alone for now.

Matt

Son of SK

[tacker]

Cheers Matt

Ok to sum up then:

6kg springs all round

white line 26mm rear sway bar ( which i have )

white line 22mm front swaybar ( which is on order )

both with sperical links which i believe it the rear has and front should when it gets here.

My thoughts are that the whole car needs to be rebushed as something is happen under the old girl so the wheels are all pointing in different direction, directly porportional to the radius of each corner. The harder you turn the worse it gets the pic above it appears that both back wheels are pointing out giving huge amounts of toe out.

Dont get me wrong your advice is sound and i will get some softer springs but have to stick with the jap shocks for a while at this point in time.

[BHDave]

Increase the rear bar stiffness if it is set to soft.

If it's still understeering then zero the rear toe as with your current problem the rear toe in won't be helping.

It will be far from optimum but it will improve the handling and cost you what ever a rear alignment costs.

Try increase the rear damping.

Then spend money on the other things.

Your grip seems biased towards the rear, so you need to try and get it back towards the front. As you can't go any softer on the front then try and stiffen up the rear.

re the sway bars, i'd say the cusco unit may be hollow which is why it has a large diameter.

[tacker]

And it is a hollow item