914-6 GT fast road/track suspension settings Options

[amallagh]

Hi,
I'm just about to have the suspension set up on my 914-6 GT project and wanted to see if anyone had any advice. I have never done this before (my first 914) and was looking for a fast road/track set up. I think the range of settings people seem to talk about on Toe and Caster is fairly small but camber settings vary wildly depending on what people want to do and type of tyres.
I know the theory about track set up and measuring temperatures across the width of the tyre but this car will spend more time on the road than track (albeit I could be called a spirited road driver!), and tracktime ain't cheap !
Suspension components are :-
FRONT -
Sway-a-way 22mm hollow torsion bars
Weltmeister 22mm sway bar
Bilstein shocks
Weltmeister camber plates
Fuchs 7X15s with Goodyear Eagle GSD3 205/50s
REAR -
Weltmeister 140lb springs or 180lb springs available - need to decide which ones are best to use ?
Weltmeister 16mm sway bar
Koni adjustable shocks (yellow)
Stable Energies rear strut tower camber brace.
Weltmeister chassis and suspension arm stiffening kits
Fuchs 8X15s with Goodyear Eagle GSD3 225/50s
Tyres will be

This is what I was planning to do based on some previous indications:-
FRONT -
Toe in(each wheel)- 10'
Camber- 1 degree negative
Caster- 6 degrees
REAR -
Toe in(each wheel)- 15'
Camber- 1.5 degrees negative

#############################################
I think these are the factory settings -
FRONT -
Toe in(combined) 20' +/-10'
Camber- 0 degrees +/-20'
Caster- 6 degrees +/-30'
REAR -
Toe in(each wheel) - 0 degrees +15'
Camber- 30' +/-20' negative
##############################################

I would welcome any advice or opinions. If anyone has any advice on initial settings for the rear Koni shocks then that would be a real bonus. All advice gratefully received and without prejudice.
Andrew

[Dave_Darling]

The hollow t-bars will be fractionally less stiff than the solid ones. They might (not sure) be fractionally larger in diameter than their "rated numbers", which would make up all of the difference.

You can do the math if you know the size of the hole in the hollow bar: The bar's effective spring rate is based on the fourth power of the diameter. The hole would take away the fourth power of its diameter, which turns out to be very little in comparison to that first number until the walls of the bar are very thin. (If the hole is half the diameter of the bar, it only takes away 1/64th of the strength!)

Since the effective rate goes up with the fourth power, you can see that going up one mm does not result in nice even linear steps...

--DD

[amallagh]

The hollow t-bars will be fractionally less stiff than the solid ones. They might (not sure) be fractionally larger in diameter than their "rated numbers", which would make up all of the difference.

You can do the math if you know the size of the hole in the hollow bar: The bar's effective spring rate is based on the fourth power of the diameter. The hole would take away the fourth power of its diameter, which turns out to be very little in comparison to that first number until the walls of the bar are very thin. (If the hole is half the diameter of the bar, it only takes away 1/64th of the strength!)

Since the effective rate goes up with the fourth power, you can see that going up one mm does not result in nice even linear steps...

--DD

You're right. Just checked the Sway Away website and they are actually 22.5mm diameter with an effective rate of 22mm. I don't have the bars out to measure them but based on your fourth power maths assumption then for the 22.5mm bar to have the effective rate of a 22mm bar, there must be a a 12.5mm hole in the middle. Sounds about right.

Sway away do 21/22/23mm effective rate bars. If the 22mm bars are most compatible with >200lb springs on the rear then it sounds like their scale of application is very top end biased if std 914 springs are about 100lbs.
I think I saw someone write that std torsion bars are 19mm. That being the case then 22mm bars are 80% stiffer than std. 180lb rear springs are also 80% stiffer than std. Seemed like simple logic to think they they should be fairly compatible. Is there some reason why this would not be the case ?
Andrew