Apex Wheels

[murph]

430 lb springs are significantly softer than stock. (well, the stiffer part of the progressive stock springs) Go with at least 600 in the rear. Performance will improve, and you won't rub.

[LivesNearCostco]

What is the rate of the E46 sports suspension stock rear springs once they're pre-loaded? I thought GC told me stock spring was progressive but once you preload it with the car's weight, it's linear at 400 lbs/inch over the working part of the spring. But I might have misunderstood, or GC might have been thinking of the E36 rear spring. I was assuming my current 430 lb/in was 7.5% stiffer than stock. I certainly don't want rear springs that have a lower rate than stock.

The next step up in rates suggested by Ground Control is around 440 lb/inch front and 547 lb/inch rear. Not sure what is after that but I guess about 500/600. What front spring rate would you suggest if I go 600 lb/inch for the rear, and what spring rates are you running?

[murph]

All depends on your application... I liked 550/650 on the street with the ASTs, might be too harsh on ground control shocks.

Vorshlag tested the rear springs at more like 600 lbs, I believe.

[LivesNearCostco]

This Vorshlag spring testing? http://www.vorshlag.com/tech_springrates.php
I clicked on the spreadsheet link and saw...

• BMW E46 2001 330Ci Front 130 lb/inch linear
• BMW E46 2001 330Ci Rear 320-380 progressive (really 360-380)
• BMW E46 M3 Vert Front 140-170 lb/in progressive (really 170+)
• BMW E46 M3 Vert Rear 350-493 progressive (really 377-493)
• BMW E46 2004 ZHP 330i Front 140 lb/inch linear
• BMW E46 2004 ZHP 330i Rear 375-750 lb/in progressive (really 440-658)
• Dinan E36 M3 front 100 lb/in linear
• Dinan E36 M3 rear 425 lb/in linear

So it appears my rear springs (and Derbo's) are same as Dinan E36 M3 rears, stiffer than the 2001 E46 vert OEM rears, but significantly lower rate than the 2004 ZHP sedan rears. Those start at 375 lb/in but assuming each back corner carries at least 800 lbs static, the working rate from 2"-4" of compression is 440-658 lb/in progressive.

Interesting... now I'm thinking I do need to try higher rear spring rates. My current rear rates (430 lb/in) are where the OEM ZHP springs start (at 2" compression), but much lower than where they end up under heavy cornering load. Your rear rates were where the OEM ZHP springs end up between 3-4" of compression.

[murph]

And I realize I never answered your question, I use 600/750 in higher grip situations, and am thinking I'll try 650/750 next year. (600+ up front gets to be a bit much on the street)

[LivesNearCostco]

When you say higher grip situations, besides the surface type, what kind of tires are you using with those springs rate--regular summer, sticky summer (like Star Specs), R-comps, or slicks?

[derbo]

thats interesting that the zhp rear is that wide of a range. I didn't know that. Upgraded springs here we go

[murph]

I use 265/18 Dunlop star specs (colder weather) and hankook RS3s. (warmer) when I say higher grip situations, I mean when it's 75+ on smooth asphalt, or 70+ on concrete. Colder weather or beat up surfaces mean less grip, and so the car rolls less, and less spring or bar is required to control camber loss.

I've logged over 1.5g's in this car in Lincoln. "high grip" I generally think of when I'm getting more than 1.2-1.3.

[derbo]

17x9 or 17x8.5?

[LivesNearCostco]

Little correction to my math. Jay of Ground Control pointed out to me that due to the lever action of the rear upper control arm, 800 lbs of corner weight applies about 1100 lbs of force to the rear springs. So if Vorshlag's published rates are correct, the static compression of the stock ZHP rear springs is about 2.5" and the spring rate at that point is somewhere between 500 and 600 lb/inch.

• BMW E46 2004 ZHP 330i Front 140 lb/inch linear
• BMW E46 2004 ZHP 330i Rear 375-750 lb/in progressive (really 440-658)

So it appears my rear springs (and Derbo's) are same as Dinan E36 M3 rears, stiffer than the 2001 E46 vert OEM rears, but significantly lower rate than the 2004 ZHP sedan rears. Those start at 375 lb/in but assuming each back corner carries at least 800 lbs static, the working rate from 2"-4" of compression is 440-658 lb/in progressive.