Suspension rates, very confused.

[FranzE21]

Hey guys, I was doing a bit of reading the other day in the Haynes manual. It says BMW has three colour's to distinguish spring rates on their factory springs, red being softest, white being midstrength, and green being the hardest.

" Coil Spring rates lbf

Front

Code Red - 688-705
Code White - 708-725
Code Green - 728-745"

" Rear

Code Red - 613-631
Code White - 633-648
Code Green - 650-666"

My confusion stems from firstly, why does everyone refer to their spring rates in lb ie most people run 400lb front and 350lb rear. I don't understand the difference in measurement types.

Secondly, I gave my springs a wipe and checked the colours, my 318i has green fronts (hardest) 23.5mm front bar (1982 standard) and yellow paint on the rear springs with a 16.5mm rear bar (factory option).

What the hell are yellow springs, I've always found it hard to understand the "wet mop" analogy for my car, perhaps its running a factory sports pack of sorts. Were the green spring rates the same as the 323i springs? and why do I have different springs rear, which technically don't exist. (im not crazy, its definitely yellow.

Thanks guys, just don't want to get aftermarket springs which are softer than the factory ones, I want a 10-15% increase in stiffness instead.

Appreciated

Franzen

[skitzone]

they sound like kings.

[FranzE21]

Sorry I didn't make that clear, the colour which is on the springs is only a little brush of paint on a random coil. about 1.5in long. My rear springs have yellow brushmarks, like the green ones up front.

[tlapham]

mine are (were) the same way, green paintpen on fronts, yellow on rear.

[Layne]

My old springs had yellow dots as well.

When people say "400lb" they mean "400 pounds to the inch" meaning it takes 400lbs of force to compress the spring 1". I suspect BMW's specs are in some sort opf metric measurement. There's no way any of them are over 100lbs/in.

[FranzE21]

Wow, even Layne doesn't know what the yellows are :P, thanks for trying though man, interesting to hear you had the same setup. Have all of you had air conditioning at some point from the factory? they said they put stiffer springs up front because of the aircon weight.

Just wanna know the exact rates of the factory springs i'm running, so when I get a set of custom springs made by the company here; I can keep almost the same ride quality but slightly stiffen the set of springs and make the car lower. Would suck to get springs which are too stiff and overpower the ability of the damper, or springs which are lower but the rates are lower, so you get soggy low suspension.

Know what Im sayin?

Thanks guys

[Layne]

All the A/C in the USA was dealer or port installed, not factory. I don't know if the factory anticipated this and equipped them with a/c springs. I find it ridiculous that they thought they needed a different spring for a 50lb weight difference. By now our cars vary by probably 200lbs or more and the same springs are fine. It's a different story from like an e32 where the different engines have drastically different weights.

[FranzE21]

All the A/C in the USA was dealer or port installed, not factory. I don't know if the factory anticipated this and equipped them with a/c springs. I find it ridiculous that they thought they needed a different spring for a 50lb weight difference. By now our cars vary by probably 200lbs or more and the same springs are fine. It's a different story from like an e32 where the different engines have drastically different weights.

Just reading what I saw in my haynes manual layne (lol rhyme), I would agree with your statement entirely though, curious do you know anyone who has a pdf scan in of the original options/accessories sheet available for the E21?

Franz

[FranzE21]

Looking at those numbers from the haynes manual .. I say that the only thing that makes sense is if they are in Newtons / cm ... so to convert N/cm

(Haynes number/9.81)/10 x 55.88 = lbforce / inch

so for the front Green spring has a range of 728 ~ 745 = 414.7 ~ 424.4 lbf/in

But the Haynes manual is almost certainly quoting Euro spec suspension Info, so the big question is how soft was the US stock suspension?

I also had this thought, but dismissed it thinking that would be crazyness to have such a comparitively soft spring on a potentially heavier car (US bumpers). Could it be possible though? Which yanks here have driven a proper euro e21 and noticed a difference?

Franzen

[skitzone]

424 lb/inch my arse. I have 320's on the front and it's a hell of a lot stiffer now.

[Madhatter]

newtons is usually per mm or m.

Just as an example, standard rear 323i ones are 701-703 lbs. However, the lbs figure is lbs/ft, not lbs/inch, so the spring rates are about 60lbs/inch.

So go through that list and you get.

Code Red - 688-705 - 57- 59
Code White - 708-725 - 59 - 61
Code Green - 728-745" 60 - 62

" Rear

Code Red - 613-631 - 51 - 52
Code White - 633-648 - 52 - 54
Code Green - 650-666 - 54 - 55

All the bold are in lbs/inch.

Edit: according to the US factory manual ive got too, the spring rates are the same.

[Layne]

I believe we have a winner! Like I said there's no way anything is over 100, because the Eibach springs are about 100lb/in and we all know those are stiffer than stock.

[FranzE21]

newtons is usually per mm or m.

Standard 323i ones are

701-703 lbs. However, the lbs figure is lbs/ft, not lbs/inch, so the spring rates are about 60lbs/inch.

I think my empirical section must be a tiny bit faded, missed that. I calculated 80lbs/inch for the front greens based on doing my own spring rate test on the car based on the alleged factory weight of 1030kg, but its not exact, just thereabouts. I wont include the maths as its not particularly..ahh important to put here (I rubbed it off the whiteboard)...

Didn't do the back yellows, of which I assume are around 65-70lbs/inch as you say.

I also had another stare at the insanely large metric numbers. Haynes is an American book right?

Either im crazy or the measurements were converted completely wrong for the metric side. According to a kg/mm test, the rates quoted would be not so much suited for good ride quality on an E21, nor a rock hard race E21, perhaps more suited to a WABCO mining truck. 333.xx kg/mm spring rate calculation.

Someone screwed up

A little closer now I think to what I was looking to achieve. 100-110lbs I think would be good for ride quality, handling and chassis longevity.

Thanks alot guys.

Layne, glad I contributed towards your ego , its been a pleasure doing business .

But seriously, cheers.