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My lap times are lower with the higher spring rates and smaller sway bars. Had too much understeer with the bigger sway bar and softer gtv6 t bar. The bigger sway bar was really torquing the front connecting points even with the welded in reinforcing plates. Car chassis seems to be happier with the higher spring rates and less sway bar.
You calculate the rear frequency with 300# springs at 2.75 which seems high but the way the springs are mounted doesn’t really damage the integrity of the chassis. Plus the rear end grips pretty well.
Since race tracks have been closed due to the virus, I’ve been driving the stiffly spring alfetta on the mountain roads around reno on cheap street tires. Roads around here are much better maintained than high traffic city streets, bumps, pot holes, and cracks aren’t as prevalent. Since it’s a stripped down race car with a full roll cage, it does feel overly stiff and noisy. The handling is very good on the mountain hairpin turns. the body roll has been minimized and you get sea sick rolling from side to side. It handles like a Miata now.
 

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I meant you don’t get sea sick rolling from side to side on the stiff suspension vs the soft stock suspension.
 

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You can't simply quote spring rates of 2 completely different suspension designs and vehicle/suspended mass.
That's why suspension 'stiffness' is spoken about as a natural frequency. You can compare natural frequencies, but the ways and means of achieving said natural frequency is vehicle specific.

Years ago I crunched the numbers to calculate the natural frequencies of different torsion bar sizes for a V6 75/Milano.
Keep in mind that natural frequency is basically wheel rate VS suspended mass. The more suspended mass, the lower (softer) the natural frequency.
So a lighter car with the same size torsion bars will have a higher natural frequency.

22.8mm TB has a Wheel Rate of 93lb/in = NF of 1.10Hz.
25.4mm TB has a WR of 143lb/in.
27.3mm TB has a WR of 191lb/in = NF of 1.58Hz.
28.7mm TB has a WR of 233lb/in = NF of 1.74Hz.
30.0mm TB has a WR of 279lb/in = NF of 1.9Hz.
32.0mm TB has a WR of 360lb/in = NF of 2.16Hz.

A V6 75, a car that has a lot more weight sitting on its front wheels than an Alfetta GTV, with 32mm TBs has a natural frequency that is 'dedicated, chassis reinforced with a substantial roll cage and running slick tyres' stiff. And that's a full weight car, not a stripped out race car.
My understanding is that road car tyres, even proper sporting types, don't do much/any better once you go past about 2Hz.
And the rear suspensions natural frequency should be 10% higher than the front suspension's natural frequency.
If I did my maths right, the motion ratio for the rear springs is 1.05:1. In squat, the rear spring compress 5% more than what the wheel moves upwards. It's very unusual to have a motion ratio higher than 1:1.
Put a spring over the front damper and it has a motion ratio of 0.3867
For a full fat 75, a rear spring rate of about 175-185lb/in gets you around 2Hz natural frequency
So if 2Hz is around about the limits of even the most useful road going tyre and the front natural frequency is 90% of the rear natural frequency, then the front should have natural frequency of 1.8Hz, or basically 28.7mm torsion bars and get rid of some of the fatness. And again, that's for a V6 75.
Can you show the different elements of the equation and various geometry that you used to come up with these wheel rates. I have done this and have come up with very different values. Just work through the 30mm bars. In U.S units please.
For reference:

GTV6 (long) Overall 990mm (38.9”) Effective length 927mm (36.5”)
Milano
(short) Overall 932mm (36.7”) Effective length 856mm (34.5”)
 

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Can you show the different elements of the equation and various geometry that you used to come up with these wheel rates. I have done this and have come up with very different values. Just work through the 30mm bars. In U.S units please.
For reference:

GTV6 (long) Overall 990mm (38.9”) Effective length 927mm (36.5”)
Milano
(short) Overall 932mm (36.7”) Effective length 856mm (34.5”)
My number are crunched on the back of the measured, by another forum member (sorry, it was a long time ago, so I can't say who it was), wheel rate of a standard torsion bar equipped 75/Milano.
To translate that initial wheel rate of 93lb/in to the other size bars, it was a function of applying a simple rate comparison calculation I learned many, many years ago
So to compare the original 22.8mm bar to the 30mm bar, you simply raise each diameter to its forth power.
22.8^4 = 270,233.6256 (no units).
30^4 = 810,000
To get the wheel rate translated from the initial 93lb/in for the standard 22.8mm bar, to the 30mm bar:
(93/270,233.6256)810,000
=0.0003441466 X 810,000
=278.76lb/in

To get that to a natural frequency, I used a spreadsheet that was shared on GTV6.com(currently out of action) that was supplied by a member and came from his 'ex-V8 Supercar race engineer' workmate.
I don't know how to share it on here.
I'm sure you can goggle how to calculate motion ratios of dampers and/or springs.
As I mentioned in an earlier post, I calculated a front damper motion ratio of 0.3867 and a rear spring motion ratio 1.05.
 

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I believe that the values that you use were incorrect. I have calculated the values some time ago and I actually chained down the car and validated them with a load cell placed under the center of the ball joint. The measured values were pretty close to the calculated values so I am pretty certain they are correct. I am cutting and pasting this from a word document so it wont post my equations because its not text. But you can google this and find them. You can ignore the numbers that state the value at the dampers - those were used to help out some guys who wanted to directly compare coil overs to torsion bars.

Equation for Torsion Bars: = Spring rate (K)

Equation for Hollow Torsion Bars: = Spring rate (K)

Where 1,178,000 = spring rate (torsional constant)

D = Diameter of Torsion bar in inches.

d = Internal diameter of hollow torsion bar.

L = length of torsion bar in inches (effective length) (only the length that twists should be calculated with)

l = length of lever arm in inches (12.37” from Lower Control Arm (LCA) pivot to the ball joint) (10” LCA to damper mount)



Torsion Bar (TB) Diameters: 27mm (1.063”) TB lengths: GTV6 (long) Overall 990mm (38.9”) Effective 927mm(36.5”)

30mm (1.181”) Milano(short) Overall 932mm (36.7”) Effective 856mm(34.5”)

31mm (1.220”)

32mm (1.260”)

33mm (1.300”) (Note: 12% more WR than 32mm)

36mm (1.417”)

Wheel Rates for Bars:

GTV6 27mm = 269 lbs/in (wheel rate) 412 lbs/in (at damper) Milano 27mm = 284 lbs/in 435 lbs/in (at damper)

30mm = 410 lbs/in (wheel rate) 627 lbs/in (at damper) 30mm = 434 lbs/in +52% 664 lbs/in (at damper)

31mm = 467 lbs/in (wheel rate) 715 lbs/in (at damper) 31mm = 494 lbs/in +14% 756 lbs/in (at damper)

32mm = 531 lbs/in (wheel rate) 813 lbs/in (at damper) 32mm = 562 lbs/in +14% 860 lbs/in (at damper)

33mm = 602 lbs/in (wheel rate) 921 lbs/in (at damper) 33mm = 637 lbs/in +13% 975 lbs/in (at damper)

36mm = 850 lbs/in (wheel rate) 1301 lbs/in (at damper) 36mm = 899 lbs/in 1376 lb/in (at damper)
 
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