Skip to main content

Hi there

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"... Eeker


Images (1)
  • IMG_20180703_1107344_(2)
Last edited {1}
Original Post

Replies sorted oldest to newest

I dont know if you accept my advice , but the new springs you have are from a Maseratie Quarteporte ?

Place one old and one new spring on each side of the car ,whit out the spacer on the new shock.

otherwise heat the new springs 2 coils from under and push them down , that lower the car 3 cm.and keep their stiffenes.
I didn't roll the car, but pushed down with my weight on each corner.

Not Maserati, generic Eibach springs

One old and one new, that's not good advice, it'll try to twist the arm and wear out joints and pivot points

Let's see if any from the US/Canada has ideas, otherwise I'll just buy 150 lbs/in springs and try them. Then I'll own 16 rear Longchamp springs...
just my first thought.

try placing a 1 to 2 board under the right rear tire to level and thus put more weight on the left and see if that lowers it.

I think the front on a center jack is an unknown as to how the weight is suspended. making sure it is a "free pivot" and moving it over to the right.

do you have the spring lenghts free and then mounted.

any way to test the rate
Originally posted by René #4406:
The springs are inleaded and the lever arm must be taken into account between the pivot / wheel and pivot / damper length. ...

Just looking, Due to;

1) the lower arm ratio of Y/X, the spring will compress less than the wheel moves.

2) the shock angle with respect to the lower arm, the spring will compress slightly more than the arm goes purely up and down


Images (1)
  • spring_force
Last edited by jfb05177
Why cut corners?

Do both sizes, but all four wheels on the car, drive it a mile or two, park the car and do the measurement!

That's what I would do if I were on a customer's hourly pay ;-) For us weekend warriors, it's sometimes necessary to work smarter, not harder... Wink

But you have a point. Took it out to drive today, raised the other side body with a jack simulating all 4 installed, it got even higher. So for me, for sure, I'm not going from 125 to 175, regardless of my math, I'll buy 150s...

Add Reply

Link copied to your clipboard.