I want to raise the rear of my Longchamp, it's too low when fully packed trying to negotiate terrible roads in Loire Valley on LMC trip. Later I'll get to the front, I started with the rear because I had the springs. They're same brand, length and diameter as the ones I had on, only variance is that they're 175 lb/in, the ones mounted before were 125 lb/in.
Here's my math on how much I expected the rear to sit higher with the new springs:
Weight of car: 1800kg
Estimated weight on rear wheels: 700kg=1555lbs
Weight per spring (4 at the rear), 390lbs
Compression with 125 lb/in: 390/125=3.1 in
Compression with 175 lb/in: 390/175=2.2 in
Variance 0.9 in
So I expected the 175 springs to raise the rear almost 1". I today mounted two springs on the left rear axle, lowered the car so it's on the ground on the rear wheels. The front is on one jack in the middle between the front wheels, so having a pivot point, so the front wheels do not touch the ground, and do not affect how the rear end sits.
Here's the problem. The left side comparing fender lip to rim lip is 6 cm higher, more than 2".
Is my method with of testing with a pivot point on the front wrong, do I have to mount the other 2 175 springs to really be able to measure (replacing rear springs on the LC is not a fun task)?
Is my math wrong? When I ask people selling springs, when I tell them I have 4, they go quiet, all their calculators can only handle 2. Having 2 springs at 125 lb/in per wheel, is that exactly the same as having 1 spring at 250 lb/in per wheel?
I understand this can never be accurate, because springs are not all the way out at the wheels, on the other hand they're not fully vertical either. But expecting less than 1" and getting more than 2"...