968cs_red

Hi,

I'm getting my M030 Koni's rebuilt and while I have them off etc was considering changing the springs to slighter higher spring rates.
I use the car mainly on track but do drive on the road too a fair bit.

Was hoping someone may be able to offer advice on this and what rates they have used.

As I understand the front standard rate is 28N/mm = 160lb/in.
The rear (helper spring) is ~ 125lb/in I read somewhere.

1) can anyone confirm the rear rate? This is not listed in the 968 workshop manual...

2) my setup would be keeping the rear torsion bar so suggestions for the new rear spring rate would have to allow for this.


thanks,
Matt.

Graham CS

Hi,

Just done this.

I went for 250lb hypercoils which work well on British roads (read crap roads)

I think they may be a little soft for the track though.

Will find out soon

Graham

968cs_red

Hi Graham,

This is the rough figure I had in mind for the fronts... my real area of interest is the rear (no jokes please! :-) )

Have you kept the torsion bar in your setup? If so what spring rate are you using at the back?

cheers,
Matt.

flash968

according to paragon and performance products, the stock rear torsion bar rate for both standard and M030 is 175# - numbers i have seen for the helper spring vary, so maybe raj has that spec

i removed the rear torsion bars altogether and went to kla adjustable shocks with eibach 250# springs - my butt-o-meter tells me that it is about 25% stiffer than stock - nice on the street

968cs_red

Cheers Flash,

Who's to argue with the tried and tested butt-o-meter then?!

I'm thinking that 250lb/in springs on the front with a combination at the rear that gives maybe around the same 250lb/in effective rate would be good.

Now I know the torsion bar effective rate I can do the calculation to find out what springs I need....

cheers :-)

Matt.

P.s A confirmation from Raj or someone on the stock rear helper rate would be great. Dots (2) on the spring are green.

968cs_red

ahh just thought... the 250lb/in springs at the front... the 250lb/in is a linear rate - so another question is what does this translate to in terms of effective rate at the front?

Obviously I need to do the calculation to work out the effective rate with a 250lb/in spring at the front - and then calculate what spring rate to use at the back used in conjuction with the torsion bar to give the same or slightly less
overall effective rate.......... i think?!

Matt.

flash968

be careful of the calculation thing - i tried that with the rate calculator at the paragon site, and the .56 ratio did not work - it kept coming out way too stiff for street - they were cool though and it all worked out in the end, but i ended up working with the engineer at eibach to do the math on the entire geometry to figure out what spring i needed to get just a bit over stock

i am currently wrestling with the decision between 225 and 250 up front to balance with the rears - i currently have eibach/tech art progressive springs and the initial rate is too low - rides nice on the freeway, but on hard turn in i think it takes too long to ge to the firm rate and gives me too much front roll

i'm going to drive dave's car again first - he has the h&r 190/230 springs - that will give me a better guage

968cs_red

Yeah I've just done the calculation for the standard M030 setup at the rear.

The overall effective rate = (0.56 x helper spring rate) + torsion bar effective rate
= (0.56 x 125lb/in) + 175 lb/in
= 245 lb/in

This seems high compared to the standard 160lb/in springs at the front?

Any thoughts? - is this due the the calculation coming out too high as you said Flash, do you think?

Matt.

968cs_red

p.s re: the effective rate at the front......... same as the spring rate as there is no mechanical advantage etc in the front setup as mcpherson struts which are mounted at the end of wishbone where wheel is also located.

So as far as I can tell the standard setup is:
160lb/in effective front rate
245lb/in effective rear rate

flash968

actually i think it's higher than that- i have to dig up my notes, but i think the effective rate was a much higher ratio - i'll do that and get back to you

where did you come up with 125# for the helper - so far i've seen rates from 50-100# on those springs - if somebody could get me the specs on the size i could calculate the rate - from pictures, i am guessing somewhere around 75#

raj? anyone?

flash968

dug up my notes and it looks like it's closer to .75 effective ratio not .56 - measurements of rested and compressed heights bear this out too - my 10" 250# springs compress 3.75" with an estimated rear load of approx 1400lbs, and stock being around 1600# - that would make a wheel rate of 188# - my butt-o-meter thinks it might be stiffer than that, which would mean i have less weight on the rear wheels than i think (very possible - haven't weighed corners since new suspension setup and car diet, and i am now at dead level ride height which may be transferring weight to the front a bit) - it definitely does not dip like stock when you bounce the rear end - very resistant to that - also does not compress under load like stock - both of these tend to make me think it's a bit higher wheel rate than 188, like closer to a little over 200

does that help or confuse things more? - i know my head is now spinning

968cs_red

Flash - thanks for the info.
Think you are right about the effective ratio. I did some measuring of the geometry last night and I get a figure of about 70% effective ratio.
Using this figure the rear effective rate works out to be (0.70 x 120lb/in) + 175lb/in = 260 lb/in

This is based on the helper spring being 120 lb/in. Can't remember where I saw this figure but I have seen this in more than one place on some sites on the web. I guess the only fool proof method is to get one of the springs 'tested' to give an accurate figure.

The springs have 2 green dots on. The green should give a value for the rate... but I've never found any info on this... I'm just going on what people have said rather than official sources... annoyingly the spring rate is not given in the workshop manual..

cheers,
Matt.

flash968

i know that frusration - i have not found a rate for that spring anywhere - it's possible because it's a progressive spring (as i've been told) and they don't want to publish a rate they can't demonstrate easily

raj or somebody may have a soucre of data on the rate - so far, as i said, i've heard of things like 50-100 - the spring looks like a 75 - i can't imagine them going higher without increasing the front to balance

Graham CS

Jason at Paragon told me it was 50 lbs.

Which would means that its effective rate would be 28lb

So in total about 200 at the wheel.

I heard that the helper spring was put on to aid towing trailers etc.

The .56 rate on the paragon site is for calculations with torsion bars.

The effective rate of the front 250 will be about 225.

Thats what Jason told me anyway.

Graham

flash968

read closer - it is intended to incorporate both the torsion and coilover springs - many conversations with jason and chuck, and second hand with skip, and so far, nobody has gotten back to me with where the .56 came from - it may have been a simple juxtoposition

no worries - we all worked it out and i got the spring rate at the wheel that i was looking for