In essence, because of these factors:

If you lessen 1/4" of preload on 500 lb/in springs, and 1/4" on 800 lb/in springs... you've altered the inherent suspension balance (and subsequent handling characteristics) of the vehicle.

If you're talking a mm or two, you wouldn't probably notice much - but "best practices" would be to get your car to a competent shop, set the ride height where you want, and have 'em corner balance at that level.

 

 

I agree with your basic physics, but they depend on tacit assumptions,
that the contact point to the ground at each corner doesn't change, and
depending on camber and suspension geometry, they may not. If the arc
of travel is different front to back, or if they are even the same, but at
different angles in their arc, then this will affect their relative distance away
from the center of gravity of the car. Don't assume your suspension positioning
is exactly the same on the left as on the right unless your last corner balance
job was also very particular about checking ride height at all 4 corners. Usually
I see the guy do it at one place on one side and one other place on the other,
and not necessarily exactly the same spot! Also, if the camber is different, the
load balance can also change differentially. Once a car has positive or negative
camber the weight is mostly on one edge of the tire, but if you raise a car enough
to go from negative to positive there is a big shift in the moment arm.
So, if you succeed in raising your car symmetrically, you will want a re-alignment,
and if you were perfectly corner-balanced before, you won't be radically off, but
you likely won't be spot-on either. But close is really all you need. Once you hook
up the sway-bars, the corner balance is only spot on for that CG. gain or lose
10 lbs, fill or empty the tank, have a passenger, put in or take something out of
the trunk, and that all changes...

 

This is a great discussion. Can you corner balance a car with just lowering springs? From what I am reading, you have to be able to adjust height in order to get the car to balance? If this is true, then the dealership I was going to buy my car from was totally blowing smoke since he told me the dealership corner balanced the car with the alignment when they installed the H&R springs.

Is there any special kind of alignment for just a spring install?

 

First you need coil overs to corner balance a car. H&R makes coil overs and they came factory on GT2-3's. Then some are better then others. I have bilsten on my car and after you balance the car you need to hook up the sway bars and if you do not have adjustable links you wind up pre loading one side to get the sway bar hooked back up. There goes your corner balance! Jic's are adjustable for that also.

 

I'm pretty sure it was only H&R springs...no coilovers. Thanks for confirming.

 

I hope this helps clarify.

 

This is where I'm confused. How does adjusting the spring perch up (or down) by the EXACT same amount (let's say 3 turns of the perch) on all 4 corners change the preload on the springs??? The body of the car is not a fixed object. It will freely move up (or down) by the same amount that you have moved the perches and the preload on the springs will not change. The only time that the preload on the spring would change would be if the body of the car was not free to move in response to the spring perch adjustment.

 

Hey Joe,
This all makes sense. Obviously the alignment will change with any alteration of ride height and would need to be redone. As you state, all the details that you mention above would come into play but their effect on corner balance in our street cars is relatively negligible/minor. I was mainly concerned with this from a purely physics standpoint (if all the other variables remained constant) with which you seem to agree.

One can start splitting hairs but after all, how do we know that the scales being used by the shop doing the corner balance are precisely calibrated and spot on? All it would take is for one scale to be 3% off and you have a 30 lb. assuming a 1000 lb. load. Or what if the surface that the scales are mounted on is not calibrated dead straight and level. Even a 1/16 or 1/8" delta would have an effect on a corner balance. I would be willing to bet that if you took a car to one shop for a corner balance and then took the same car to another shop across the street for another one, you would get very similar readings but they would not be an exact match.

 

well said....

 

Yep, and unless the person doing the first corner-balance is careful to
shake the car during adjustments to make sure there's no stiction holding
some part from settling as far as it will, you might be able to roll the car
off the scales, onto the shop floor, and roll it back onto the scales and
get some different numbers than before. Note that when you raise or lower
a corner, if the tire on that end has any traction at all, you impart a side-
load (the wheel doesn't go exactly straight up or down) which pushes or
pulls the car a little. Now if one or other corner may have less traction or
side-load resistance, such as having a little more or less grease on the
surface, the side-load on one side might displace the body that much!
Heck, next time anyone here has their car on the rack for a corner
balance write down the initial numbers, then before changing anything,
just lower or raise one tire's pressure by 4 lbs. Tell us how the corner
weights changed.

 

The answer is yes. I agree that on a street car the perfect balance is probably not needed but it will change if you adjust it no matter how evenly you think you are doing it. I raised my ride height also a smidge but had it rebalanced. It is worth the money to have it readjusted especially if you track it.

 

Well put!