why 964RS has smaller rear anti-roll bar?
10-27-2009, 09:32 PM
#1
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why 964RS has smaller rear anti-roll bar?
Dose anyone know why factory design a smaller rear anti-roll bar and bigger one for the front for 964RS (compared with C2)? What is the weight saving compared front & rear? I guess most of the weight saving are from the front, such as the seats, aluminum hood, aluminum wheel carrier, side glass, door panels...
10-28-2009, 12:31 AM
#2
Rennlist Member
It's not about weight its about effective spring rate and adjustability. The RS has higher spring rate in the coilovers and the front and rear bars are adjustable to tune the handling characteristics. Here's a comparison of the RSamerica/C2 030 rear bar and the RS adjustable piece:
10-28-2009, 08:01 AM
#3
Drifting
A smaller rear bar also helps to reduce overstear. I got a lot more traction out of the corners when I changed to the RS bar, and I ran in it the softest position. Then when I got the LSD I also put a RS bar in the front to balance the increased traction from the LSD, and this also made it possbile to set the rear bar in the middle position. Now I'm really happy with the balance, turn in, and traction.
10-28-2009, 08:49 AM
#4
As has been mentioned the base springs for the RS are very different
here are the f/r spring ratios, lower means stiffer rears relative to front and greater native oversteer
'89-91 C2/4 0.836
'92-94 C2/4 0.894
mit M030 0.727
RS 0.606
Cup 0.75
Eibach Pro 0.977
H&R 964 green 0.962
H&R 965 red 0.947
H&R 964 Cup 0.664
H&R performance street 0.641
Weltmeister 0.672
I also have #s for PSS9 and KW v3 but they don't make sense so I suspect faulty data loking fo better #s on PSS9, PSS10, KW all
here are the f/r spring ratios, lower means stiffer rears relative to front and greater native oversteer
'89-91 C2/4 0.836
'92-94 C2/4 0.894
mit M030 0.727
RS 0.606
Cup 0.75
Eibach Pro 0.977
H&R 964 green 0.962
H&R 965 red 0.947
H&R 964 Cup 0.664
H&R performance street 0.641
Weltmeister 0.672
I also have #s for PSS9 and KW v3 but they don't make sense so I suspect faulty data loking fo better #s on PSS9, PSS10, KW all
10-28-2009, 12:33 PM
#5
Three Wheelin'
Interesting numbers. It would seem that the H&R green/red setup is much more understeer-inducing than factory. Exacerbating the problem for us C4 folks.
10-28-2009, 12:46 PM
#6
Rennlist Member
I have often wondered if a combination of HR Red rear and Green front springs would be a good combination for a C4.
Bill, do you have the numbers for a Green/Red F/R ratio?
I have sets of both - I am tempted to try it, in my spare time someday.
I have already put the 21mm rear bar (largest stock available) from a 90 C2 onto my C4 (originally with 20mm). I know it is not much of a difference, but I think I can detect a difference. But, what do I know, the nut behind the wheel has the greatest room for improvement.
Bill, do you have the numbers for a Green/Red F/R ratio?
I have sets of both - I am tempted to try it, in my spare time someday.
I have already put the 21mm rear bar (largest stock available) from a 90 C2 onto my C4 (originally with 20mm). I know it is not much of a difference, but I think I can detect a difference. But, what do I know, the nut behind the wheel has the greatest room for improvement.
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10-28-2009, 04:54 PM
#10
Nordschleife Master
Most every steel comes in there at around 11,000 ksi for torsional modulus ("G").
It's drastically more efficient to affect a torsional stiffness change via diameter than material changes, based on the torsional deflection equation:
alpha (torsional deflection) = TL/(GD^4),
where T = torque, L = effective torsion bar length, D = bar diameter.(fourth power variables are an engineer's dream control agent.)
10-29-2009, 09:33 AM
#12
Drifting
Thomas
10-29-2009, 04:56 PM
#13
Burning Brakes
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"...Most every steel comes in there at around 11,000 ksi for torsional modulus ("G").
It's drastically more efficient to affect a torsional stiffness change via diameter than material changes, based on the torsional deflection equation:
alpha (torsional deflection) = TL/(GD^4),
where T = torque, L = effective torsion bar length, D = bar diameter.
(fourth power variables are an engineer's dream control agent.) .."
Oh come on Lonnie... Everybody knows this...
It's drastically more efficient to affect a torsional stiffness change via diameter than material changes, based on the torsional deflection equation:
alpha (torsional deflection) = TL/(GD^4),
where T = torque, L = effective torsion bar length, D = bar diameter.
(fourth power variables are an engineer's dream control agent.) .."
Oh come on Lonnie... Everybody knows this...
10-29-2009, 05:59 PM
#14
Nordschleife Master
hmmm... good point.
(This might explain why my girl friend's eyes roll whenever I 'explain' how her car works...)
Executive Summary: The bar's diameter, not its metal, is what car builders alter to change a sway bar's stiffness.
Well, that and its end pickup points...
(This might explain why my girl friend's eyes roll whenever I 'explain' how her car works...)
Executive Summary: The bar's diameter, not its metal, is what car builders alter to change a sway bar's stiffness.
Well, that and its end pickup points...
10-29-2009, 11:16 PM
#15
Rennlist Member
I always wondered how the adjustabilty of the RS sways works. I have both set at the middle holes of each bar. Works great. What does moving the bar to the other holes do?? Is there a combination of adjustment for the front vs the rear that is more optimal?