I Need Your Suspension Advice , Can You Help ??

[MX339]

Thanks for finding that. Nope, I don't have a diagram, but that one will work nicely. I've been looking for the archived version of Gustav's site. Lots of good info on there.

Will

It spooked me a bit when the old site went down a few weeks ago, but the guys on S14 had an archived link. I know I'm still getting plenty of use out of it.

Thanks, yes,
that's about what I was thinking of.

I get in mental trouble switching between the 2002 and the E30,
because they're not exactly the same... but similar...

t

The properties of the roll center shouldn't be any different on our 02's, they're both McPherson anyhow (E30's and 02's that is).

What I tend do to is just think of the 2002 front suspension being backwards of the E30's. You've got the radius rod in the front of the 02's subframe while the steering linkage is behind it. While the E30's are the other way around, even though the control arm is pulling double duty acting as the radius rod too.

[ajackz]

Ping for later reading.

[TobyB]

Thanks, yes,
that's about what I was thinking of.

I get in mental trouble switching between the 2002 and the E30,
because they're not exactly the same... but similar...

t

[BlackbirdM3]

I assume you're looking for a more detailed/E30 specific diagram, Toby, but here's a basic roll center diagram for those of you who don't quite understand it.



The accompanying article is located here: http://web.archive.org/web/200712300..._transfer2.htm

Thanks for finding that. Nope, I don't have a diagram, but that one will work nicely. I've been looking for the archived version of Gustav's site. Lots of good info on there.

Will

[MX339]

Will,
do you have a roll center diagram for the front kicking around anywhere?

t

I assume you're looking for a more detailed/E30 specific diagram, Toby, but here's a basic roll center diagram for those of you who don't quite understand it.



The accompanying article is located here: http://web.archive.org/web/200712300..._transfer2.htm

[TobyB]

Will,
do you have a roll center diagram for the front kicking around anywhere?

t

[BlackbirdM3]

can the extra body roll from the roll center be combated with the strut tower bars ???

Strut tower bars just tie the left and right sides of the car together better. As the suspension compresses it will cause the strut towers to move toward each other, since they are angled in. A strut tower brace simply keeps them from compressing inward. The same thing applies to the rear shock mounts. They are supports, they don't affect the suspension geometry.

With a bad roll center, the common band aid fix is going with crazy high spring rates to combat the effective loss of spring rate as things compress. The trade off is that the suspension doesn't move unless its a big hit. This causes the car to feel nervous because you have no suspension travel until you hit something big/hard enough to overcome the spring rate. (Think of it like a mountain bike with the suspension locked out. It doesn't absorb the little stuff, but it moves if you land a jump or something along those lines.) On the street the car fails to absorb expansion joints and that sort of thing. Yes its flat through a corner, until you happen to find a bump then the car skips. This will make the car feel loose because it is. All your grip is what the tires can provide, and if they are skipping off stuff, they aren't on the ground.

If you get the roll center correct, and reduce the spring rate so that little stuff is absorbed as well as the larger stuff, the car will be faster, and easier to drive because the suspension is moving and absorbing impacts allowing the tires to stay on the ground. Suspension movement is a good thing.

A couple years ago I got to drive a friends M3 with GC coilovers and it was nervous and skittish. It was not settled, and the rougher the road the harder it was to drive. It always felt like it was right at the edge of tire grip. We then swapped cars and he drove mine. The difference was night and day. Even with my spring rate way too low, and the roll center being way off, the car felt planted and confidence inspiring until you hit a bump and then it would bottom out and hop. We had opposite ends of the spectrum, although he was closer to the right roll center because he had the spacers that go between the control arms and the strut. Still the car was hard to drive at the limit because it just felt unsettled everywhere.

There are a few other things that come into play besides roll center that dictate how a car handles. Roll couple is another. This can affect how weight is transferred under braking and acceleration. It also has to do with the roll centers of both the front and rear suspensions. Getting things right is really a matter of compromise. What you give up to get elsewhere. For a perfect smooth flat or banked track (Think NASCAR) give up roll center for higher spring rates and a lower ride height to gain an aero advantage, for say Nuremberg, you have only one super fast sections and a whole lot of corners that have different profiles. Raise the car up and trade a few mph of top end for more grip in the corners. The corners are what matter, and the more speed you carry through them, the faster the lap you will have. In the case of street driving, I'd trade looks and top end speed for good suspension geometry any day of the week. I'm not saying you want a 4x4, but there is a point where lowering the CG becomes detrimental to the roll center and your gains from lower CG are lost to the loss of suspension geometry. Its all about going as low as you can go without driving the RC below ground.

Will

[JRKOUPE]

I hope the OP doesnt mind .....but its all relative...

HR race springs for e30m3 is a widely used spring in our e30's, even used by spec cars, and iirc they are like 315/550 or so...and it is a rock solid planted set up, just a bit soft for advanced DE stuff or all out racing. I dont understand why or how then a 500/700 set up would then make a car so loose? \

these rates are all over the web..most are accurate enough, if not perfect, how could all these company's get it so wrong?( in terms of frt to rr set up):

Stock 325is: 118/265
Stock 325i: 106/245
Stock M3: 140/250
Eibach Pro: 148/274-343 progressive
Eibach Comp: 166/457
Dinan Street Sport: 171/300
H&R Sport: 185/340
H&R Race 315 570-680
H&R Grp G (not DTM) springs: 343/570,700,912
H&R Coil Overs: 340/380
Turner J-Stock: 680/1026
Alpina: ~200/350

[TobyB]

I think you may have your rates backwards,

Whoopsie, yes, I fucked up- 700 rear, 600 front was loose,
700 rear, 650 front was better.

Yes, the RELATIVE difference was pretty night- and- day at Portland.
Adding #50 all around I'm sure I wouldn't notice, especially there with the nice smooth pavement.

Single yellow Konis, stock sway bars, about 5 1/2" off the ground (flat of rocker) in front,
a tad more in back.

t

[JRKOUPE]

nrub..

you say "you are way off base here.."...do u mean blackbird or the OP?...

Spring rates:The common set up IS for higher rear rates, but dont assume what Toby mentions is wrong. I just last week spoke to a well respected raCER who also uses more rate up front on his e 30 and he says the car is very very stable. Im confused as well as I hAve some 550/700 rates ready to install.....and now Im worred..lol

but when Toby states going higher in frt from 650 to 700 the rear became loose makes kind of no sense/..Toby?...

I believe its your pro3 car correct?.....dont most of these guys run more rate in rr vs frt??...like most of us.


and I agree on sway bars.....Im not sure id even bother w/ upgrades


Matt....your comment made me feel better.....what was so bad about the 450 all around?..just curious.

and could u tell between the 600 vs 650 in your buttmeter?



and..this:

Also, the point of the short stack camber plates is that they allow you to lower the car and retain suspension travel. In fact, with short stack camber plates and shortened struts, you may well gain travel, depending on your ride height choices.


is spot on!!!!
__________________

[Paddlee30]

can the extra body roll from the roll center be combated with the strut tower bars ???

[e30_302]

1" roll center spacer, puts the arm right back where it should be (I'm using factory strut mounts). Needs a 16" wheel.

[BlackbirdM3]

I haven't personally taken the measurement, but a friend of mine (who is a rocket engineer, and therefore understands precision) did some roll center measurements and calculated the roll center as 2" above ground at a ride height of 12.6" fender to wheel center.

Roll center correction matters. A lot. But you are way off base here.

Also, the point of the short stack camber plates is that they allow you to lower the car and retain suspension travel. In fact, with short stack camber plates and shortened struts, you may well gain travel, depending on your ride height choices.

And what setup are you running to get that? If your lower control arm points down toward the ball joint, yes I'll believe it. If the control arm is level or sloping inward toward the oil pan, I'll say double check the measurements. If you have roll center spacers, again, sure I can see that as being possible, but your control arms will be sloping down toward the ball joint rather than inward toward the oilpan. I'm not the only person who says this either. http://www.massivebrakes.com/accesso...llCenterSpacer A quote straight from the ad "If your control arms are at (or close to) the horizontal, then their geometry is compromised" If the total height from the ball joint to the top of the strut mount is less than X inches long, the geometry cannot be correct. The thing that dictates this (for the most part, I'm sure there are possible combinations of strut housings that allow for spacers to be run or something. Another possible way to do this is to somehow raise the subframe) is the extended length of the strut insert because the mount attaches to the top of the strut. A topped out strut is just that, topped out. It can't be any longer and so cranking the preload on a set of coil overs to the moon is doing nothing but compressing the spring and inviting coil bind when it compresses.

As for the short stack camber plates, they rub on the upper spring hats. I'll call that a bad design. I've talked with GC and they swear there is no contact, but after looking at the tops of my correct spring hats, they are scuffed and scraped to hell. There should be NO contact here at all. They might work fine with coil overs, but since they supposedly are designed for spec E30 that must run H&R race springs, its a bad design. I sent pics to GC when I questioned them on the fitment and I was told it was fine. WTF? I thought perhaps I had been sent the wrong part, but apparently not.

To answer what roll center is and why its important, it has a very big impact on how the suspension works. Here is a quick article that I found. http://www.meganracing.com/tech/faqs...ect=Suspension Some of the major downfalls to having a roll center that is too low are more body roll, to correct this you run more spring rate, but the spring rate effectively falls off the more the suspension compresses (because the already bad roll center has moved) You also tend to loose camber as things compress, and a Mac strut suspension already has issues with this. The quick and easy solution is to run mega high rate springs, but the draw back is the need for dampers that have been valved to handle the high rate springs, and the tendency to have the car skip over imperfections in the road rather than absorb them (making the car feel nervous all the time)

This might be worth messing around with. http://performancetrends.com/rc.htm

If you are using stock strut housings with the spring perches removed, and threaded inserts added, (like a GC setup) your total stack height is still dictated by the strut insert because the gland nut still needs to be screwed into the top of the housing in the stock place keeping the off the shelf damper in place. Really the only thing you gain with coil overs is the ability to get cheap springs at different spring rates. You can make it lower, but unless you have a damper with the extended length that is long enough to keep the roll center above ground, the full height will have to be made up by using spacers either between the bottom of the strut housing and the control arm, or by adding them to the top of the mount, or both as I have to do.

Will

[matthugie]

Your springs seem to be either too stiff in back/too soft in front.

650 front/600 rear and stock sway bars makes mine pretty neutral, as one starting point.

700 front/600 rear made it a bit more tail- happy than I was comfortable with..

t

His spring rates are pretty standard. I think you may have your rates backwards, pretty much no one runs stiffer fronts than rears. I've also driven a car that had 450's all around and it was rubbish. The rears were switched out for either 600's or 650's and the handling improved greatly.

[TobyB]

Your springs seem to be either too stiff in back/too soft in front.

650 front/600 rear and stock sway bars makes mine pretty neutral, as one starting point.

700 front/600 rear made it a bit more tail- happy than I was comfortable with..

t

IGNORE THIS- I MUST HAVE BEEN SMOKING SOMETHING