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In Reply to: Re: will this suspension setup workout? posted by RA/Bob G. on December 18, 2000 at 21:28:47:
1. Anti-roll bars. These reduce the body roll of the car, without lowering the car. It is a viable option for those of us who want to reduce the roll of a car without resorting to stiffer springs. What an anti-roll bar does is tie the two ends of the suspension together. The stiffer the anti-roll bar is, the less it wants to bend. This resistence to bending is it's spring constant (or "k"). The higher the spring constant, the less it will travel with the same amount of force acting on it. (F=kx, if you increase "k", "x" or the distance traveled, is reduced if you keep "F" constant). The less travel you have in the suspension, the stiffer the suspension is. Thus, if you want to reduce roll, but want to keep the stock ride height, bigger anti-roll bars are the way to go.
2. Springs. The stiffer the springs, the less they want to travel. The less travel, the less roll, dive, and other suspension movement you have. Lowering springs have increased stiffness because you have less spring travel, and you don't want to bottom out the spring. This is why if you want to get lowering springs, they are stiffer than stock. (Again, do the calculations, and you will see). And this is why cutting stock springs is bad. This is because the spring constant remains the same, but the total amount of spring travel is reduced (because you're reducing the length). Thus the maximum amount of force you can exert on the spring is reduced (F=kx, if you reduce x, and keep k the same, you reduce F). Thus, you can bottom out the suspenion on severe bumps, potholes, etc.
3. Shocks. These do all the important work of DAMPING the spring. If you have just a spring, and put a force on it, and then remove the force, in an ideal situation, the spring will oscillate FOREVER. Think about a slinky. Of course, there are frictional and other forces action on the spring which will dissapate this. Now, your shocks do the work to dampen the spring's oscillations. If you have a soft shock, it is not doing much work of dampening the spring's oscillations, and thus you have bouncing. If you have a hard shock, it will do a lot of work dampening the spring's oscillations. Now, a soft shock feels cushy, a la Cadillac. If you've ever driven next to one, and seen it go over a bump, you will see it boucing up, and down, and up, and down....Now, if you drive next to a Ferrari or something like that, you won't see that, because the shocks will dampen the spring's movements. (Of note, almost 99% of suspensions are underdamped, in theory. The perfect damping is when the shock does enough to work so you only have 1/2 of a period. You hit a bump, the suspension compresses, then it rebounds to the original length it had, but we won't get into specifics here.) But, the important point is that the shocks are the key to a well handling and BALANCED suspension.
4. Tires. What contacts the road? A small patch of tires. THEY make all the difference in grip. If you run R-compounds, you have mucho grip in dry, none in rain. There are soooo many variables to consider with tires, that it's better to recommend a good, all-round tire and wheel combination. With tires you have to consider:
A. Sidewall deflection - (Generally, less deflection, more stiffness, less "give and suppleness". This is why 17" wheels give a harsher ride than 15")
B. Total area of contact patch - (Generally, more tire on the road equals more area to grip)
C. Shape of contact patch - (The idea of a friction circle. If you have a wider tire, you generally have more lateral grip, the thinner the tire, the less lateral grip. Remember back in the 50's when F1 tires were skinny? They had to "slide" the cars to get the maximum speed in corners. Nowadays with slicks (well, until 1998), you practically "drive on rails")
D. Temperature - (Generally, a tire that's made to work at a higher temperature will not work well at lower temperatures. This is one of the reasons why a performance tire - made to work at high heats, and grip well there - will be solid as a rock and give just about as much grip as a plastic Power Wheels tire in cold weather or low temperatures)
E. Camber/Caster adjustments to make the tire work effectively - (you want the tread to wear evenly, so that you have EFFECTIVE use of the contact patch.)
F. Tire compound - (Similar to the temperature issue, the tire is designed to work in certain grip conditions like snow or rain or dry, and at certain temperatures).
G. Tread design.
As you can see, it can get complicated, really quickly.
Now that we've gotten that out of the way, here's some of the options we have available for E28's. I'm only going to do Springs and shock combo's for now.
(Note, all spring rates are given for front springs, and used to compare relatively between springs).
1. Stock springs (165 lb in), Boges
This is what the 535i originally came with. Hey, there's nothing wrong with this, it was state of the art in the 80's, and it's still better than 90% of what people drive out there.
2. Stock springs (165 lb in), Bilstein HD
The Bilstein HDs an aftermarket replacement shock that fit with Stock springs (or generally, +/- 0.5" of stock spring ride height). The damping of the HD's is more than the Boges, and can "firm" up the handling from stock.
3. Stock springs (165 lb in), Koni Reds
Not too readily available, but Koni Reds are made for stock spring heights, and are adjustable. Very cool because you can adjust the damping for "performance" if you want, or "daily city driving."
TO BE CONTINUED
I have bilstein HDs I should have got sports. But, i didn't. So, don't lecture me on why you shouldn't lower shock like these, it is done with stock shocks on new cars all the time. Besides, I am using what I have. I was planning to lower them with H&R springs from BMP, use a stress bar from BMP, racing dynamics sway bars, and upgrade to 16inch wheels with 225/50's. I am trying to accomplish a ride that will not give me as much body lean in turns. With the hd's it is not where i want it to be. Can anyone tell me is this resonable setup that will work? Please help.
josh
thx
535i to is
Colorado
Josh;
Bilstein Hd's are perfect;the sports will be far to harsh for the ride you say you want.
On body lean,that is eliminated more by springs and swaybars,not shocks.I've been setting up e28 cars for years,and my own outcorners "M" cars regularly,using Eibachs,Koni or Bilstein HD's,and RD or SuS.Tec. swaybars.And you still have 85% if a normal road ride.
I use 16x7.5" rims with 205/55/16 or 225/50/16 tires,adding a 3.73LSD diff and 7 series brakes.
Great combination;you have 25% more usable power,M5 handling, BETTER than M5 braking,and it's still comfortable all day long.
Of course,lately I've gone to 17x8.5" rims and 245/40/17 tires,but that's for an instructor's track car.
You also need to reinforce the center swaybar mounts,as well as the rear shock towers if you plan serious driver's school rides,along with new 7 series control arm bushings,and new "a" arm and subframe bushings as well.
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