I did it the same way you did at first but I used a mm scale more accurate. My ride height was at 55mm all around with my weight in the car and the correct fuel when I autocross.
Took it to my sponsor who does corner weighing and I was off by like 2 turns on one corner. You will notice better handling when you get it corner weighed though.
__________________
Sponsored by: KAM Racing Sports, Falken Tires, Progress Technology, Brady's High Performance, Taggart Performance Engineering, Rotora Brakes
Autocross is: 90% driver, 5% car, & 5%
CRAZY MOJO!
Autocross Help Page