Oversteer mania...

[erik325i]

You need to stiffen those suckers up for sure.
I had mine set at about half way when I first installed them, and they were bouncy as fuck.
With those rates, you should be close to full stiff even if you are just driving it on the street.

-Erik

[mazur]

That's on the street. I've always done that with coil-overs figuring it'd give me a good ride.

Otherwise it's about 0-1/4 turn from full stiff front and maybe 1/2 turn back in the rear. Havn't really been able to chose something concrete yet.

Are you guys suggesting to run the same on the streets as on track?

[matt]

Yeah, full soft doesn't sound right. With those rates, you should be approaching full hard, probably.

[golde30]

you run the shocks at full soft? when i ran them at full soft my car bounced around like hell...

[mazur]

So did you pull your rear bar?

Oh, yah...I did. Havn't been to the track yet, but going around some nice sweepers by the dealerships here, I can tell the rear is getting more grip and doesn't want to just slide out.

This is with shocks at full soft front/rear.

Oh, and it's getting corner balanced Wed...can't wait to test it out at PIR!

[surebimmer]

So did you pull your rear bar?

[JeffRR]

Here's a screen dump from my spreadsheet, the items in the dark blue cells are the ones we've been talking about, Left side = inputs and right side in the box = outputs. Sorry its not so neat as its a working doc that I threw together some time ago.

I'm a chassis engineer and this is one of the spread sheets that I use to determine initial set-ups for a prototype. My buddy and I were talking about direction for our e30s so I tossed in some numbers I found on the web so we could us it as a reference.

There is a wheel rate calc but I'm using it to get to ride rate which really is what we're after, its a way of comparing different vehicles since it takes out the vehicle weight.

I pulled a bunch of the numbers I used as inputs from that e30m3performance site.

There are quit a few assumptions in the spread sheet but its a good tool for determining direction and magnitude of a change for steady state spring and sta-bar tuning. (that's why i use about and approx)

The formulas are pulled from various common vehicle dynamics text books, pulling a little hear and there as I needed or found useful.

[erik325i]

Is the swaybar worth anything? It's from an IS. If not I'm gonna toss it.

It's really only worth anything to someone with an early 318 because they didn't come with any from the factory.
I have thrown away a couple of those swaybars.

-Erik

[matt]

Don't toss it, you never know when you might want to go back to regular springs or something.

[mazur]

Thanks for the link. Been to the site before but had forgotten the address.


So I took out the swaybar and adjusted the ride height a little in the rear. It's slightly lower. Pics below.

Is the swaybar worth anything? It's from an IS. If not I'm gonna toss it.

[matt]

Very nice info.

If it isn't too much trouble I'd be interested in the forumla's you used to figure all that out. Or at least the conversion from spring rate to wheel rate on the E30.

http://e30m3performance.com/tech_articles/susp-tech/eff_rate/eff_rate.htm

You'll need to know some assumptions he's making (or measurement's he's made) of the sway bars to come up with the relative roll stiffness the calculated.

[mazur]

I did a few calcs, the 450/750 springs should give you a ride rate of approx 2hz. Which is in the range for a track set-up.

Ideally the rear ride frequency will be 10~15% higher as a rule of thumb. Ideally you'd set your base spring rates using a level ride theory with the rear ride rate higher than the front, something in the neighborhood of 2.0hz front and 2.3hz rear. Then balance out the OS/US with bars. but based on available parts balancing only with bars might not be an option.

With a few more cals it looks like your total roll stiffness distribution is in the 50/50% front/rear range (stock bars and 450/750 springs). By pulling the rear bar your shifting that distribution to approx 55/45 FR/RR. That's a pretty big shift in roll stiffness distribution and will give you a good direction. Not to mention its simple.
For reference you'd have to drop to a 600lb/in rear spring to have that similar roll stiffness distribution (similar to dropping the rear bar).

A few more calcs and with the Ireland 25mm front/19mm rear (not adjusted moment arm same as production bars), M3 front drop link mount and 450/750 springs you'd be around 53/47 Fr/Rr roll stiffness distribution.

Anyway, pulling the bar is free and fast. It'll confirm that your going in the right direction and as budget allows you can add bars and get back to a similar balance, while maintaining an acceptable roll rate for a track car.

Very nice info.

If it isn't too much trouble I'd be interested in the forumla's you used to figure all that out. Or at least the conversion from spring rate to wheel rate on the E30.

[erik325i]

Pull your rear bar NOW.

You are running a kickass setup for an e30 with NO rear bar.

I agree completely.

I am running the C3 kit with 450/750 springs, NO rear swaybar and a cabrio front swaybar. I loved how it handled at the track. It was very neutral.

-Erik

[JeffRR]

I did a few calcs, the 450/750 springs should give you a ride rate of approx 2hz. Which is in the range for a track set-up.

Ideally the rear ride frequency will be 10~15% higher as a rule of thumb. Ideally you'd set your base spring rates using a level ride theory with the rear ride rate higher than the front, something in the neighborhood of 2.0hz front and 2.3hz rear. Then balance out the OS/US with bars. but based on available parts balancing only with bars might not be an option.

With a few more cals it looks like your total roll stiffness distribution is in the 50/50% front/rear range (stock bars and 450/750 springs). By pulling the rear bar your shifting that distribution to approx 55/45 FR/RR. That's a pretty big shift in roll stiffness distribution and will give you a good direction. Not to mention its simple.
For reference you'd have to drop to a 600lb/in rear spring to have that similar roll stiffness distribution (similar to dropping the rear bar).

A few more calcs and with the Ireland 25mm front/19mm rear (not adjusted moment arm same as production bars), M3 front drop link mount and 450/750 springs you'd be around 53/47 Fr/Rr roll stiffness distribution.

Anyway, pulling the bar is free and fast. It'll confirm that your going in the right direction and as budget allows you can add bars and get back to a similar balance, while maintaining an acceptable roll rate for a track car.

[mazur]

I sure don't!

I'm still skeptical about running no rear bar, especially if you're running street tires. High spring rates (>500lbs) are going to heat up the tires faster, and if they're street tires that aren't designed for high temps, they are going to get greasy quick, killing your overall grip.

Decrease your rear spring rate and keep the bar in.

But hey, I'm a wuss on 350/475 springs

I don't think they're that stiff. I can still depress the suspension pretty easily when pushing down on the trunk. My E36 with 500/550 springs wouldn't even budge. E30 wheel rates are pretty "soft".

And since I'm getting 245's all around when my current tires wear out, I think I'll be able to deal with the heat just fine.