E30S50

[|ncary 0]

Got new springs, 575lb fronts and 500lb rear, but put some 170lbs in the rear for shits and giggles but it didn't really make much difference

I'm sure my PM was clear enough about why you need the rear spring about 1.5 to 1.7 times harder than the front! Why so soft in the back? Have you gone coil over shock with rear tower reinforcement? Or are you saying you have 1000lb springs in the rear, making it 500 effectively?

And that 170 rate you would feel if you drove it, it'd understeer and lift inside front wheels like a bitch all day

[c.robertson00 11]

That looks f@#kn sweet mate

[Jamez 2147483647]

Were just going springs in the rear with no coil overs, reason for low spring rates is that some of the other cars at raceFx are using 200-300lb rear springs and they are all heavier in the rear, will probably end up putting a slightly harder spring in, I still have 500lb springs that can go in the rear.

all will be revealed round the first corner might have to get it on video

Edited July 27, 2009 by Jamez

[|ncary 0]

With effective rates of 550f and 250r it's certainly going to have a lot more rear traction than front. Car's are fastest when set up to understeer slightly, so you'll have to see how it goes

[Jamez 2147483647]

with effective rates of 550/250 it will have a similar setup to the blue Z4 at RaceFX that can do a 1:03:900 with the right driver

that car does have an extra 70hp but is also a bit heavier, so who knows how the e30 will compare

Edited July 27, 2009 by Jamez

[|ncary 0]

Oh yeah? Well certainly with the right driver, and some help from sway bars and good shocks, it'd have excessive traction out of corners, which is perfect for track work heh

[CamB 48]

200lb on a trailing arm <> 200lb on a coilover, due to the different motion rates. If the Z4 has coilovers, its very, very different.

For the same reason, you can't simply work off a ratio (like 1.5-1.7x) as it changes as the springs get harder (the wheel rate is what you need to work out).

[|ncary 0]

I'd like to actually measure up the trailing arm and see what the actual rate of a given spring would be. Internet might have it somewhere.. I know however it's not exactly 50% wheel rate from a given rear spring, so halving it to get actual rates is a bit of a guess.

But, it wouldn't change as the spring gets harder though.. The point where the spring sits, the T-arm perch, isn't moving so the wheel rate would always be a constant percentage of the spring rate, no matter what rate the spring is. I believe.

(Well you could get into things like: as the trailing arm swings up, the spring perch in the front to back axis moves backwards a couple of cm and changes geometry, but negligable really)

Hmm actually reading what you said again Cam, I have misread. Certainly for the rates I have chosen, having the back rate 1.59 times harder than the front rate has worked out very well for balance. I don't see how though it would matter if you wanted say a 700lb front rate and a 1125lb rear rate (1:1.6) it should give the same handling balance. But much bumpier

[|ncary 0]

Wham. I love Gustave.

http://www.e30m3project.com/e30m3performan...e/eff_rate2.htm

Front is Spring Rate times .88

Rear is Spring Rate times .45

Using my car as an example:

350 x .88 = 308lb/in wheel rate (or 5.50kg/mm)

550 x .45 = 247lb/in wheel rate (4.41kg/mm)

308+247=555

Front rate is 55% of total, rear is 45%, weight distro of car (stock anyway) is 52f/48r.

Rear is under sprung slightly, and front is over sprung slightly. Giving more rear grip on a skid pad or well executed corner, exactly what a E30 needs.

What a speel!

Didn't do these calcs before I ordered my rates, but it has worked out perfectly. RESEARCH FOR THE WIN.

Hijack over

[Jamez 2147483647]

nice, for me

575 x .88 = 506 69.2%

500 x .45 = 225 30.8%

so using your formula thats 70% front 30% rear combination

or if I put the rear spring on the front and the front on the rear I get a closer combination (both are 6" springs)

500 x .88 = 440 63%

575 x .45 = 259 37%

hmmmmmmmm

Edited July 27, 2009 by Jamez

[|ncary 0]

Hmm yes yes, it's over twice as hard at the front, not sure how that would drive.

I'm sure your weight distro hasn't changed too much with a cage mostly in the back and a bit more weight in the front. Balancing spring rates to weight distribution on the wheels is key for handling as I've read. Centre of Gravity balancing is another thing all together, something for DTM and F1..

You should get your car on some corner weight scales when done, the results of that will be curing curiosities everywhere

[CamB 48]

I don't see how though it would matter if you wanted say a 700lb front rate and a 1125lb rear rate (1:1.6) it should give the same handling balance. But much bumpier

Incary - try running the same equations for the 600lb front and 1125lb rear and you'll see what I mean

James - so is it coilover rear? Or using the standard inboard spring perches on the trailing arm?

Edited July 28, 2009 by CamB

[Jamez 2147483647]

using the standard inboard spring perches on the trailing arm

[CamB 48]

When RaceFX say they have success with the lower rate springs on the Z4, if its coilover the motion ratio might be over 90% since the spring is moving almost directly over the hub. This means that 250lb for a coilover is probably the same stiffness as 500lb in the standard E30 location.

If they say it will work then its worth trying. I am sure to some extent it will also depend to some extent on your choice of rear sway bar and the weight distribution as a race car (nothing in the rear half = front weight bias, at least in my car).

Edited July 28, 2009 by CamB

[|ncary 0]

Incary - try running the same equations for the 600lb front and 1125lb rear and you'll see what I mean

James - so is it coilover rear? Or using the standard inboard spring perches on the trailing arm?

Hahaha yes I realised after I found the motion ratios that those rates wouldn't work. You are just wonderful Cam

[|ncary 0]

Hang on hang on, the calcs do work out. If you had a 700/1125 setup, thats still effective rates of 55%f and 45%r.

It's all linear, but of course!

The 1.6 ratio is sound.

[CamB 48]

Ooops - you're right. :o

I was doing numbers in my head. If you stick with a ratio front/rear you are ok.

If you add 100lb front/rear, not so much.

Either way, what I really don't know is how to change the theoretical to the practical --> what difference does all this make in real life. Theoretically my rear springs are woefully underdone, but the car was pretty well balanced.

[DRTDVL 0]

Ooops - you're right. :o

I was doing numbers in my head. If you stick with a ratio front/rear you are ok.

If you add 100lb front/rear, not so much.

Either way, what I really don't know is how to change the theoretical to the practical --> what difference does all this make in real life. Theoretically my rear springs are woefully underdone, but the car was pretty well balanced.

Driving style and personal handling preferances also play a big part...

[|ncary 0]

I thought my car was very balanced before, with King Springs, went like a champ. Now with uprated springs that are matched to the weight distribution, the rear grip is SHOCKING (good shocking), it doesn't have that E30 tendancy to get the rear end out in slaloms and under power, it's a completly new car. Certainly the style you drive with matters though.

[hybrid 1044]

I decided on medium track setup for NZ's sh*t bumpy track surfaces 525f/700r with a medium/hard shock.

Most DTM rates are around 1000 mark and 1175 rear. With those rates youll want reinforced / rebuilt rear towers and reinforced rear trailing arms perchs / seam welded body and ties to all major hard points tied to the roll cage.

[Jamez 2147483647]

this may shock some of you but its not running a rear sway bar to start out with

[Guest FrantiC]

only 325i's had rear sway bars.

320i, 318i dont.

mounts are there to add one though, I did on mine.

Edited July 28, 2009 by FrantiC

[E30-323ti 66]

this may shock some of you but its not running a rear sway bar to start out with

Not really surprising, I don't run a rear bar, and just a stock one up front.

BUT I am running coilovers in the rear with 350# springs.

Are you sure those 250's you are using are not going on coilovers??

Because in the stock location that rate is about the same as stock springs at ~244# (which equals a boat)

Edited July 28, 2009 by E30-323ti

[Jamez 2147483647]

yeah, the guys at raceFX reckon it dosent really need one, also delmonts turbo beast dosent have one

they keep on stressing to keep the car soft

[E30-323ti 66]

yeah, the guys at raceFX reckon it dosent really need one, also delmonts turbo beast dosent have one

they keep on stressing to keep the car soft

Don't confuse "soft" with "supple" there is a difference!!! (same with "hard" Vs "Firm")