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Spring rate section
Spring rate effect on acceleration, FR
Red is 2.0/2.0, blue is 20.0/20.0, both using 130/130 ride height and simulation tire.
  
  
 
Red with soft spring rate has slower acceleration, but it also has better braking distance.
Spring rate effect on acceleration, FF
Yellow using 20.0/20.0 spring rate, black using 2.0/2.0 spring rate, both using 135/135 ride height, 24/24 BBC.
  
 
Black with soft spring rate has slower acceleration, but it also has better braking distance.
This is the same from FR car result.
So in summary, in GT2, hard spring rate can increase car acceleration, although it can also increase braking distance.
Spring rate effect on cornering
With the help of computer driver, I can get a stable lap time. This make cornering testing possible. The track is Super Speedway. The car is 472hp 1710kg 3000GT VR-4 Turbo
Using 2.0/2.0 spring rate.
 
Using 20.0/20.0 spring rate.
 
Using hard spring rate increase the cornering grip. The cornering speed is higher when using 20/20 spring rate. The turning capability also higher when using 20/20 spring rate which can be seen as more distance from the wall.
Spring rate effect on acceleration, 1000m
Another 1000m experiment, curious with different feeling on spring rate behaviour, lower front = more oversteer?
NSX Type S Zero, stock with FC suspension = 1/1 1/1 damper, 0.0/0.0 camber, 0.00/0.00 toe, 7/7 stabilizer.
spring height time
2/2 135/135 24.554
4/4 135/135 24.515
6/6 135/135 24.493
8/8 135/135 24.48
10/10 135/135 24.479
12/12 135/135 24.435
14/14 135/135 24.444
16/16 135/135 24.446
18/18 135/135 24.477
20/20 135/135 24.481
2/2 135/135 24.554
2/4 135/135 24.518
2/6 135/135 24.595
2/8 135/135 24.58
2/10 135/135 24.576
2/12 135/135 24.568
2/14 135/135 24.554
2/16 135/135 24.559
2/18 135/135 24.547
2/20 135/135 24.553
2/2 135/135 24.554
4/2 135/135 24.648
6/2 135/135 24.641
8/2 135/135 24.641
10/2 135/135 24.645
12/2 135/135 24.636
14/2 135/135 24.639
16/2 135/135 24.638
18/2 135/135 24.643
20/2 135/135 24.643
2/12 135/135 24.523
4/12 135/135 24.46
6/12 135/135 24.508
8/12 135/135 24.459
10/12 135/135 24.455
12/12 135/135 24.435
14/12 135/135 24.453
16/12 135/135 24.451
18/12 135/135 24.454
20/12 135/135 24.452
2/2 89/89 24.644
4/4 89/89 24.619
6/6 89/89 24.597
8/8 89/89 24.586
10/10 89/89 24.575
12/12 89/89 24.569
14/14 89/89 24.544
16/16 89/89 24.556
18/18 89/89 24.557
20/20 89/89 24.557
12/12 89/135 24.095
Another test, spring rate effect on 1000m time.
NSX S Zero Civic type 300zx turboSilvia R AeElan S2 '64 Elise 190 Trueno BZ-R
2/2 24.554 28.879 25.701 26.454 32.325 26.429 28.686
4/4 24.515 28.854 25.652 26.419 32.266 26.395 28.637
6/6 24.493 28.839 25.621 26.388 32.223 26.362 28.628
8/8 24.480 28.838 25.608 26.371 32.202 26.340 28.548
10/10 24.479 28.824 25.596 26.358 32.180 26.328 28.571
12/12 24.435 28.791 25.608 26.330 32.172 26.302 28.569
14/14 24.444 28.809 25.573 26.347 32.161 26.305 28.594
16/16 24.446 28.789 25.570 26.325 32.153 26.295 28.567
18/18 24.477 28.790 25.553 26.327 32.149 26.289 28.552
20/20 24.481 28.782 25.556 26.311 32.138 26.226 28.564
Conclusion:
- spring rate have effect on grip. There is optimum grip value, which can be different on each car and can change on other setting change.
- handling behaviour is different when you use bellow optimum grip or above optimum grip.
- the most optimum grip is when you use the same value for both front and rear.
- because NSX is MR, high height have better time
- in NSX the optimum grip for 135/135 ride height is about 12/12. So using 4/12 or 20/12 will result in understeer, and 12/4 or 12/20 will result in oversteer.
- spring on non driven wheel have no effect on acceleration.
- lower front do not always result in more oversteer, if both value is bellow optimum grip it will result in understeer. If both value is above optimum grip it will result in more oversteer.
- from testing the result in some FF and FR car, using 12/16 will result in more oversteer (actually less push understeer/ less understeer from WOT) and using 20/2 will also result in more oversteer. In some MR car and high powered car, using 16/12 will reduce spin caused by tourqe steering, I use this setting on TVR speed 12 on rome night.
- the optimum grip is usually happen above 12 and steady after that or decrease a little on some car.
My Opinion
Spring rate will:
- increase grip, affect acceleration and cornering.
- reduce weight transfer, affect body roll (camber) and brake balance (BBC)
- increase wheel response to the road, affect damper and stabilizer.
Changing spring rate will also need changing:
- Damper, try make the wheel return to zero after bump before encountering next input. See from the wheel cam. Too soft will make the wheel return to zero too quickly, make it overshot. Too hard will make the wheel don't have time to return to zero for the next bump.
- Stabilizer, treat like sideways damper.
- Camber, increasing spring will make the wheel less angled during cornering (less body roll), so, you have to reduce your camber when you increase the spring rate.
- Brake controller.
We can use spring rate to:
- Reduce oversteer / increase understeer, reduce front spring rate / increase rear spring rate.
- Increase oversteer / reduce understeer, increase front spring rate / reduce rear spring rate.
- Grip driving, use drivable all hard spring rate with appropriate damper, camber and stabilizer combination.
- Drift driving, use drivable all soft spring rate with appropriate damper, camber and stabilizer combination.
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