Arthur McDonald wrote:
Why disconnect the sway bars?
Because as you raise or lower one corner, you twist the bar and transfer load to or from the other side adding pre-load to the bar. After all the adjustments are complete (with the bars disconnected), you then adjust the endlinks (yes mine are adjustable) so they just slide into the swaybar hole (this is done with the driver in the car) so there is no preload on the bar. If you do this without the driver in the car, the weight of the driver will pre-load the bar. If the bar has preload, as it enters a corner (say left) it will have to untwist before it can transfer load, while in a right turn it will transfer load immediately.
I didn't mention it, but I also disconnected all the shocks because as the perches are adjusted up or down, it tends to bind the spring. After each adjustment we bounced the car vigorously at each corner - you could hear the spring go BOING as the bind was relieved. Then we rolled it back onto the scales. You really can't do this with the shocks connected because the dampening works against you. Obviously, if you have a strut suspension you can't do this either.
Other tips:
You want a really flat garage floor - I actually took the car and scales to a friends house because my floor is like a hyperbolid paraboloid (it ain't flat).
Air up the tires to what you would normally run.
Roll the car off the scales to make adjustments. I have blocks the same height as the scales set directly behind them.
Make sure the tires are in the center of the scales. We fussed around with this a while then chalked the tires to make sure we rolled it back to the same spot each time.
Ride height:
There is enough adjustment to drag the rockers, but that is not a functional ride height. I went back to my data acquisition files from VIR and CMP to find the max vertical Gs (max load on the suspension). 25min on the track generates about 25,000 data points - so 4 sessions gives me lots of data. At VIR, max vertical was 1.38g and it occurred at the bottom of hogpen as you might expect (max lateral Gs also occurred there - 1.53g. That's why that corner is so much fun!). At CMP max vert of 1.23g occurred while jumping the curb at T3.
I have alot more available travel in the rear than the front so lets start there. Let’s say we’re going to lower the car to the point where we have 2.5” of suspension travel before hitting the bumpstops. For simplicity, let’s say we have 900lbs resting on each front wheel. I haven’t weighed the wheels, tires, knuckles, control arms, strut, spring and CV shaft, but I guessing there’s about 150lbs of unsprung weight at each corner - leaving 750lbs of sprung. Based on our data, we design for a maximum 1.5g bump. Based on these assumptions, we would be absorbing a 750*1.5=1125lb force over 2.5”, therefore requiring a minimum wheelrate of 1125/2.5=450lb/in.
Of course wheel rate and spring rate are not the same, but they a related by a constant that is a function of the control arm linkage ratios, the instant center of the front suspension and angle of the spring. On my car, I found WR=0.64SR or SR=WR/0.64 Therefore we, need a 703lb/in spring to handle a 1.5g bump in 2.5 inches. The new front springs I just installed on my bilsteins are 700lb/in.
I set my front ride height leaving myself the 2.5" of available travel and then adjusted the rear to give me about 3/4" of rake. When you put the car on the scales and have an imbalance in cross weight, you can correct it by adjusting any one of the 4 corners as the screen shot shows. You choose which corner to adjust by comparing the ride heights at each corner with the intent of getting them equal along with the cross weight. In the end, I got the fronts within a 1/16" and the rears within an 1/8" with the rear being about 3/4" higher than the front.
Yeah, I know - too much time on my hands. When you share a house with 4 women, you spend alot of time in the garage.
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