There's a problem with your math. A driver does not sit over one wheel. Nor can you simply spread the weight out over 2 diagonally opposite wheels. If you did, it would actually end up spreading the weight across all for tires. Adding a driver will actually add weight to all 4 wheels since the driver, for the most parts sits between all four tires. The static weight on the driver's side will be increase a little more than the passenger side. The front to rear distribution will probably be close to 50/50. That being said, if we were to assume for argument's sake that all the weight of the driver were to go to the driver's side and be distributed evenly to each of those wheels, the change is not nearly what you say it is.

First off, the crossweight difference you calculated of 52 lbs will not change:

LF + RR + 90 = 1781 lbs
RF + LR +90 = 1833 lbs

1833 - 1781 = 52

Secondly, crossweight is evaluated not and a difference, but as a percentage. 52 lbs has a greater effect on a 2000 lb car than on a 4000 lb car. So:

(RF + LR)/weight of car = Crossweight percentage

No driver:
1743/3434 = 50.75% Pretty good for any factory car. Race cars should typically be between 49.5 and 50.5(50% is where you want to be).

with driver:
1833/3614 = 50.71%. The change in crossweight is not much and in fact due to the increase in overall weight, the crossweight percentage became slightly better.

As you can see, it is not as drastic as you make it seem. Even with a progressive rate spring the car should not see a noticable difference in the change in ride height simply from swapping springs. As I have repeated, I think something is wrong with his spring or the way it was installed. I understand the logic you are using, but simply put, there is not going to be so drastic a situation that the situation you describe should exist. In fact, if it did, the car would have been uneven from the factory, even on linear rate springs and likely dangerous to drive.

 

ckwik - I see. Does the driver side really distrbute evenly 90lbs / 90lbs ith the front
passenger side and also 50/50 with the rear making it 45lbs per corner, or would it
be more biased to the driver front side, for example like this? (My guess)
(righthand drive car)

180lbs driver
LF 37.5 RF 75
LR 35 RR 37.5

Based on my guess, cross weights are going to be like this...
LF + RR + 75 = 1766lbs
RF + LR + 110 = 1853lbs

Going by your precentage with driver:
1766/3614 = 48.9%
1853/3614 = 51.3%

Would the above have enough impact to change corner weights with
a driver say on a 274~463lbs progressive rate spring?

 

It would infact distribute some weight to all 4 wheels. However, on a front to rear basis, it would depend on where the seat is in relation to the wheels. Looking at the diagram on Road & Track's data page, it looks like te front seats are pretty well centered. I'd say if there was a front bias, it would be minor. Maybe from the legs protruding forward from the seat. The seat position would probably make a slight difference a well.

As far as progressive rate springs, when you put a spring in a car it compresses from the weight. Depending on the design of the spring, much of the progressiveness of a spring is taken up just by the car's weight itself. For the most part, lowering spring companies do this because the overall higher rate of a lower spring makes a spring too short to be extended fully within the seats while providing the lower stance. So by the time the spring is compressed to it's normal ride height, it is closer to the higher rate rating. Some progression may still be left, but for the most part, most of the lower rate potion will already be in coil bind and likely at a higher rate than the factory spring. Easily verifiable by simply comparing the difference in deflection between a stock car and one on lowering springs. Simply pushing down on a corner of each car will show you the difference. All cars I've lowered have been stiffer than OEM. But to answer your question a driver's weight can certainly make an impact on each individual corner weight regardless of OEM or aftermarket spring. But the crossweight percentage will change very little in either case.

 

ckwik-thanks.

It's ironic how progressive rate lowering springs are sold as an
economical way of lowering a car while engineering such variable rate
spring should take more engineering and durability test costs than
an ordinary linear rate spring. or perhaps there is nothing ironic
about this at all... maybe it is the other way around where making
a perfectly linear spring is much more involved than making a blurred
rate spring which we call "progressive rate."

At the end of the day, the progressive rate might be just a mere
half-assed simlulation of a helper spring in a coilover system and
the unlucky ones get stuck with uneven height on the corners
due to poor engineering and or craftsmanship due to cost. It's
basically a hit and miss and most of us get hit with the miss while
we, in our heads, think the blurred rate is actually helping our
ride comfort...well, it is a little bit but it's more of a psychological
marketing tool for the manufacturers. And we have accepted this
as part of having lowering springs thinking that the corner weights
of the car were causing the uneven drops when the blurred
springs themselves are probably the root cause. Who knows what
the spring rate is while the car statically sits on the springs.

But from the manufacturing perspective, what do you expect
for a $12-$15 piece of coiled metal? Who would buy a
$500 (or watever) perfectly wound progressive rate spring?
You just have to pay if you want the perfect setup...and I
guess we have to thank the manufacturers for giving us the
option to be able to choose for ourselves.

 

The problem with aftermarket progressive rate springs is not that they are progressive. It's that there are no shocks to match their progressive rate. There are plenty of OEM cars that use some progression, but the shocks are valved to match. And due to the arc of wheel travel during suspension movement, there is some natural, but very linear progression already built in(some more than others depending on design), but add in progressive rates that are not damped properly and you end up with a suspension that is usually less than optimal. For the street, you can usually get away with it, but when looking for max performance, they are usually not the best compromise unless you are willing to build or find shocks designed for the progressive rate of those springs.

At least according to what Eibach stated in their tour, they try to ensure the most consistency from spring to spring, testing after just about every process, and testing several important aspects of the spring. They claimed that their rejection percentage was quite low. I do not remember exactly what was said, but I remember thinking that considering how many springs they spit out, if they are doing what they say they are, then the rejection percentage was very low. And if it is all true, then it would appear their quality control in the manufacturing process itself is quite high.

Personally, I'd feel comfortable buying their products based on that info and from my personal experience with their products before. However, if I were to be in the market for it, I might look more at their ERS line of springs to be coupled with a well designed shock/coil-over system. Not to mention they are based in CA which is where I am and their facility is pretty nice. They have a garage area, shock dyno, and full machine shop where they can make custom bits and pieces to suit specific needs. Not bad if I get serious about building a track car.

 

That's another issue, but that's true.

I have D-Specs on the way.

 

Where can I buy thses white Rubber donuts?