ALFAGTV6.COM

OK, I'm a bit board here and have been thinking about some of this stuff for a while (read: to long) .

Scrub Radius: From my observations of other cars, the 75 has a fairly aggressive scrub radius. The SZ/RZ even more so .
Apart from load on the steering components, what other disadvantages are there from having a high amount (for a road car) of scrub radius? I see many cars with much lower scrub radii.
This brings me to my second (rehashed) query:

Increased Track Width: With a decent camber curve, I have enough negative camber gain for the front tyres to clear the top of the wheel arch even if I add 20mm spacers behind the wheels I have.

Coil Overs: I would ideally like to go a pure coil over set up and ditch the torsion bars.

So my current thoughts are:

To make new wheel hubs that reduce the scrub radius. I recon I can move the wheel mounting flange in by between 12-15mm with the wheels I have, before I have clearance issues with the brake calipers.

Make new upper and lower control arms that allow for not only the reduced scrub radius of the different wheel hubs, but also increase the front wheel track by a total of 40mm over current. At the same time remove the need for torsion bar splines (not really an issue) and move the lower ball joint forward to give more positive caster without clearance issues.

My desired move to a stand alone coil over set up raises a question.
I would like to use a 375lb/in coil spring per side. Nothing massive, but technically the chassis isn't designed for it. Apart from my viewtopic.php?f=10&t=3403, which I believe would be sufficient, do others see any potential long term durability issues with the chassis and a pure coil over set up?

375lbs w/o torsion bar? Sounds VERY soft to me, where did you come up with that number?

Longer control arms/steering arms + higher ET rims? Did you think about that option?

It's a road car, Mats
A 375lb/in spring is very close to a 28.7mm torsion bar in wheel rate (at standard control arm length and wheel offset).

I think there may be a degree of northern versus southern hemisphere misinterpretation here regarding wheel off sets.
I see the standard (well, with the rims on my car) scrub radius as being very positive. The steering pivot intersects the road on the inner edge of the tyre foot print.
What I'd like to do is to have the steering pivot point intersect the tyre foot print closer to the center of the tyre.

Did you remember to square the MR?

A 375lb/in spring is very close to a 28.7mm torsion bar in wheel rate (at standard control arm length and wheel offset).

I can confirm this number, I'm running also 60 [N/mm] additional helper springs in line with the shocks on top of the standard torsion bars in my daily driver.
In the back side I'm running 35 [N/mm] springs.

And in my opinion, yes this is what a standard transaxle needed from factory

[N/mm] to help to total confusion
60 [N/mm] = 342 [lb/in] ~ 28 [mm] torsion bar in wheel rates

A 60N/mm PLUS the stock torsion bar? I reacted because I read 375lbs/inch springs ONLY, i.e. without the stock torsion bar.

"My desired move to a stand alone coil over set up raises a question.
I would like to use a 375lb/in coil spring per side."

Still sounds ok?

Still sound ok, standard torsion bar is neglect-able (~ 18 [N/mm] in wheel rates).
Going from 18 to 60 [N/mm] is already a big step in the right direction.

Mats wrote:Did you remember to square the MR?

The MR???

Just for the record, I calculate that the standard TB are equivalent to a 150lb/in spring over the shock absorber.

Another question relates to spring durability. I currently have a 10" long, 105lb/in, 1.875" diameter spring sitting on a threaded platform that sits on a sleeve I welded to the Koni Yellows (Yeah yeah Mats, but that's what I have at the moment ).
Now, would there be a durability issue with using stand alone 1.875" 375lb/in springs?
http://www.speedwaymotors.com/AFCO-1-7- ... 23772.html

Duk wrote:

Mats wrote:Did you remember to square the MR?

The MR???

The Motion Ratio.

How did you weld anything to a gas shock? Drain it or just dumb luck?

welding on a shock your brave!

My calcs say 169 lb/in at the shock, which was a pretty rough estimate, so we talk in the same order.

I'm running this setup ~20k km, i looked for a right length of spring eg which just engages when the car is on its wheels. This is something you can't do when you want to run a coil-over only setup.

Haha! Koni Yellows are low pressure. I used gas welding and managed to pop a hole in each 1. They needed to be overhauled anyway because (I didn't know this at the time ) they were both stuffed from excessively low ride height (the valves at the bottom were farked).

I calculated motion ratio to be 0.62 for the shock.

Maurizio, did you add any bracing to cope with your extra spring?

Thanks, Scott

scott.venables wrote:Maurizio, did you add any bracing to cope with your extra spring?

Thanks, Scott

At the chassis side, I did nothing.
The static main load is taken by the original torsion bar, as the helper spring only just touches the upper spring pad in a rest state.

On my nurburgring/trackday 75 which runs a real coil-over setup with 105 [N/mm] springs + tb's, I added some metal at the top of the shock tower.

Duk wrote:Haha! Koni Yellows are low pressure. I used gas welding and managed to pop a hole in each 1. They needed to be overhauled anyway because (I didn't know this at the time ) they were both stuffed from excessively low ride height (the valves at the bottom were farked).

I calculated motion ratio to be 0.62 for the shock.

Ignorance is bliss...

MR depends on rife height, I suspect you did your measurements with the wheel off and the suspension in full droop?