mater

Has anyone here ever try a square set up on a 996 cup. By square I mean same spring rates on each corner?? Thanks!

FTS

Out of curiousity and learning purposes: why would you want to have same/similar roll resistance front and rear, while 60+% of weight is in the rear?

analogmike

It depends on the lever ratios on the suspension as to what the actual wheel rates are, which is all that matters. I thought they DID have the same spring rates front and rear.

FTS

My bad. I thought that you adjust the motion ratios using the spring and A/R rates to achieve a target roll resistance to generate desired lateral weight transfer. I guess it is the other way around.

911SLOW

They do, although the motion ratio is not the same between F and R.

Glen

Ive run square with 360 NM all the way around,currently the car is square with 300 nm all around. the 360 was difficult for a codriver to adapt to but the 300 he was fine with.

911SLOW

: )

Glen why you think the maxed out the rates in latest cups so much?
Is it due to the wider tyres mainly? I don't believe anything else major changed in the suspension or weight..

IPguy

What are the f/r motion ratios for a 6GT3?

Is the 7GT3 the same?

Thanks,

911SLOW

I measured MR and it is a bit less than 1:1 for the front and about .75 for the rear in a 6GT3.

I believe that it should be quite similar for the 7.1 GT3 as the suspension's geometry is almost identical.

IPguy

^interesting....since wheel rate = motion ratio ^2 X spring rate (spring angle ignored for simplicity)
for some common applications (assume 0.98f and 0.75r, based on SLOWs post above):
600/800 - WR=576.24/450 - 56%/44%
700/900 - WR=686.07/506.25 - 58%/42%
900/1100 - WR=864.36/618.75 - 58%/42%

Cup rates: (converion = 5.710143)
2005 - 240/260 - 1370/1484 - WR=1315.75/834.75 - 61%/39%
2009 - 260/260 - 1484/1484 - WR=1425.23/834.75 - 63%/37%

Need sprung weight to figure frequency, IIRC.

911SLOW

Correct, hence i find it weird that cups and RSRs run same springs front and rear.

To calculate suspension frequency:

SF= (187.8)x(√WR/Sprung Weight) *sprung weight= cars corner weight less the un-sprung weight

that will give us the cycles per minute and then to find suspension frequency in hertz we divide SF/60.

or we can use the constant 3.133 to get the frequency in Hz directly.

(3.133 is 187.8 divided by 60)

claykos

My opinion about the spring rates (high in the front even though the car is tail heavy):

Due to the lightly loaded front tires, they can handle a lot of load transfer and still operate in a good spot on the load curve in terms of overall vertical load.

The rear tires are already doing a lot and we want to transfer as little lateral load as possible across the back.

We also need to consider sway bars which could dramatically alter the overall roll rate distribution.

IPguy

^the factory Cup rates seem to agree....

911SLOW

Very good point.