Setting up 4wd for tarmac..

[RS13]

My mate is having trouble getting his GT4 (ST165) trackcar to turn in, even off throttle mid corner he's having trouble getting it to bite, and hes' quite keen to learning how to set up the car himself.

We've noticed that we're getting bad tyre wear on the outside of the right hand tyre, and on the inside of the left hand tyre around Ruapuna, which is largely a right-hander track.

Short of dialling in more camber on the right front and possibly less on the front left, what else can we do? In terms of suspension, he thinks that by softening the front right, thereby putting more load on the wheel, (together with an increase in camber) would get it to bite. I would have thought that more stiffness would be better?

Thoughts?

[B1NZ]

whiteline rear swaybar

[Malcolm]

In terms of suspension, he thinks that by softening the front right, thereby putting more load on the wheel, (together with an increase in camber) would get it to bite. I would have thought that more stiffness would be better?

Thoughts?

Your mate is kinda right, but for the wrong reason. One of the most basic, basic, initial things to do when doing suspension tuning on any vehicle is to get the roll-stiffness distribution at the right balance front to rear. The numbers aren't important for what he's doing, but basically he should stiffen the end with the most grip (or soften the end with the least) either with springs or anti-roll bars, until the steady-state handling balance is where he wants it. When you stiffen one end of the car in roll, you increase the weight transfer that occurs at that end, which DECREASES overall grip at that end. It sounds kind of counter-intuitive but it is due to the load sensitivity of the tyres (as you increase the load on the tyre, you get diminishing returns as to the amount of lateral grip it can generate).

Once the roll-stiffness distribution is correct, you can then start playing with camber and toe to extract more grip (and may find you need to adjust roll-stiffness as you go)

Which is a long-winded way of agreeing with B1NZ, a properly sized rear ARB is what he needs, and whiteline are the people to get it from.

[Twolitre]

Good advice from Malcolm there and also try reading some articles on autospeed.com.au and whiteline.com.au
Whiteline make a anti lift kit for the st165 which also adds positive caster which helps turn in. They used to list front and rear swaybars for the st165 but for some reason their site no longer lists them however I'd expect an ST185 rear bar to fit fine.

[RunningRich]

Get as much caster as you can on a ST165. Whiteline (from memory) make front lower A arm rear bushings that have an offset hole. Gains a degree or two of caster. Also get as much camber as you can, I used to run 1-2 degrees from memory and I still wore the outside shoulders of the front tyres.

Improve turn in with a little toeout on the front, this improves turn in but makes it figidity on the open road.

I ran Bilstein coil-overs on mine:

http://gtfour.supras.org.nz/suspension.htm

Also check the quality of the rear bushings and consider urethane. DON'T replace the metal pivots with urethane as you can buy them new from Toyota now, the urethane caused rear end waggle:

http://gtfour.supras.org.nz/bush.htm

This setup resulted in a very neutral car with a hint of oversteer.

[strx7]

More caster helps turn in on 4wd's no end, It generally reduces the amount of power on push thru the corner too. WRX's legacy's, evo's GT4's etc all suffer from it, and caster is your friend.

[85AW20v]

On my AW11, I adjusted the rear bar one hole stiffer - I had it different from right to left - and it made a big difference to the amount of push through the corners. It's now much better to drive but at the next playday, I'll be stiffening the back up some more to see what happens. I do get some oversteer - which is controllable - if I carry too much speed into corners(read outbraked myself!!). All I've done is welded tags along the top of the swaybar with holes drilled about 30mm apart to get the adjustment.

[Mr Revhead]

be aware that adjusting the bar unevenly each side stiffens it unevenly....

[Mr Revhead]

ah, here we go
http://www.whiteline.com.au/default.asp?page=/alignment.htm

[d1 mule]

Ruapuna, which is largely a right-hander track.

that may be your problem there man, ruapuna is a LEFT handed track

note: racing direction is Anti clockwise
http://www.canterburycarclub.co.nz/Track/Maps.php

GP track 7 left. 3 right
Club track 6 left. 2 right
B track 5 left. 2 right
A track 3 left (5 left. 1 right with dipper)

[Malcolm]

be aware that adjusting the bar unevenly each side stiffens it unevenly....

Are you sure about that?

[Mr Revhead]

well, i havnt done any testing that would give me any data to argue with whiteline

Asymmetric is the opposite to symmetric and implies the use of differing holes on each side of the swaybar. For example, this might involve setting the left hand side to the hardest setting of 3 while the right hand side might be set to the middle setting. Contrary to what some people think it does not equally split the rate difference between symmetrically using setting 3 and setting 2. That is, the resultant rate is also asymmetric with more roll stiffness on one side compared to the other.

go to the above link, and click on faqs, then swaybar faqs

[Malcolm]

Actually yeah I don't know why I said that I was thinking about things all wrong

[RS13]

Ruapuna, which is largely a right-hander track.

that may be your problem there man, ruapuna is a LEFT handed track

note: racing direction is Anti clockwise
http://www.canterburycarclub.co.nz/Track/Maps.php

GP track 7 left. 3 right
Club track 6 left. 2 right
B track 5 left. 2 right
A track 3 left (5 left. 1 right with dipper)

Hah yeah, my bad, must've been tired. Now the tyre wear makes sense!

[d1 mule]

lol yeah maybe, i no nothing about racing 4wds but that just seemed a bit weird

[KinLoud]

Understeer - as has been said... stiffen rear and/or soften front with spring or swaybar.

BUT... realise that driving technique can affect handling
I have seen a couple of guys driving Lotus Elise's at Taupo making them understeer the whole of the old sweeper because they jumped on the brakes and then turned the wheel waay too quick=understeer.

I'm not suggesting that driving skill is causing the problem but it can be a factor.

Uneven holes in swaybar...
The problem is that without adjustable length links there might be a weight bias.

Ken
Auck
021 408 863

[RS13]

I'm not suggesting that driving skill is causing the problem but it can be a factor.

I would say not? Hes' been racing rwds for years, but 4wds are a completely new thing for him, perhaps that could be an issue, but I doubt it would make too much of a difference.

So then ideally we should; increase caster, increase camber on the front right, decrease camber on the front left, and get a swaybar for the rear, and perhaps soften the front a little?

[pc]

got adjustable shocks? Try softening the front a little, or stiftening the rear.

[Mr Revhead]

hell theres a bunch of adjustments to do!
personally i would start by looking at tyre pressure
then camber and castor
then adjusting shocks (if you can)
then a rear bar

my philosophy is to soften things rather than stiffen things. or rather get away with the softest settings you can.