Given the same force input at both positions on the bar, the part that's getting left out is, that the angle of twist in the bar is different because, at the inner position (short lever arm) it takes more force to twist the bar through the same angle.

Example Problem:

Two MINIs depart Denver in a westerly direction at 9 AM and motor up Golden Gate Canyon at 70 MPH. MINI #1 has the MINI Madness bar set to the forward position. MINI #2 has the MINI Madness bar set to the aft position. Upon entering the first corner, MINI #1 slows to 50 mph. Since MINI #2 is following, it slows to the same speed for the corner. For simplicity, assume that at the apex of the corner, both MINIs will have the same loads applied to their suspension, since they follow the same arc through the turn. Explain why MINI #1 corners flatter than MINI#2.

(insert flashbacks to word problems in 7th grade math here )

Answer:
The force acting on the bar is independent of where the drop links are positioned (forward or aft). Thus, the only difference between the MINIs is where the link is positioned. Positioning the link in the forward position will result in the force (called X) to act on the bar with a shorter moment arm. The angle of twist in the bar is proportional to the torsional loading. Since MINI #1 has a shorter moment arm acting on the bar, it will have less torsional load, and thus, the bar on MINI #1 will be more resistant to twisting than the bar on MINI #2. The force transmitted side to side is the same in each MINI, but MINI #1 is kept flatter because the angle of twist in the rear sway bar is less due to the forward positioning of the drop link.

 

from dave: "The force transmitted side to side is the same in each MINI, but MINI #1 is kept flatter because the angle of twist in the rear sway bar is less due to the forward positioning of the drop link."

that clears most of it up for me...thanks. in fact, the same argument applies to a thicker sway bar = less twist in the bar.

now, how does less twist in the bar contribute to less roll? Hmmm...If the bar were infinitely stiff, there would be zero roll (the roll-stiff chassis would lift off entirely the inside wheels...the complete opposite to indpendent rear suspension)

 

Correct. Which is why when the drop link is in the rearward position on the MINI Madness bar (essentially the stock geometry, but with the stiffer bar), the MINI Madness bar is approximately twice as resistant to twist as the stock bar (see calculation above), assuming both bars have the same modulus.

However, if you move the drop link to the forward position, the moment arm is cut by what appears to be about 20%. The result of just the change in geometry is a 25% increase in stiffness. Calculated by: 1/(1-.2) = 1.25

So, with the MINI Madness bar (twice the stiffness of the stock bar) at the forward position (approximately 25% stiffer than the rear setting), the result would be a 250% increase (2 X 1.25 = 2.5) in torsional stiffness compared to the stock rear sway.

 

>>So, with the MINI Madness bar (twice the stiffness of the stock bar) at the forward position (approximately 25% stiffer than the rear setting), the result would be a 250% increase (2 X 1.25 = 2.5) in torsional stiffness compared to the stock rear sway.


Well that explains why George @ Madness said "with that setting you could do 360s without effort".

R

 

Davbret: how'd things go today with your install?

 

i just saw that as I was asking for an update in this thread, you posted an update to the H&R thread

Too bad about KW shipping the series 1 springs.

 

I just posted an update to the H&R spring install thread.

Basically, I got the rear sway and rear springs installed. I was sent pre-March build front springs though. So I'm waiting till tomorrow to finish up. The correct sprints are being overnighted to me.

But as far as the rear sway goes, pretty simple actually. Here's my advice on the install:

Remove the strut completely first. Then remove the drop link nut with a 16mm wrench and 5mm allen. Then remove the binding post thingy. Next remove the 4 16mm bolts for the subframe. Then as you push down on the subframe, pull the sway bar up and back (towards rear) over the subframe mounts. Once it's in front of the mounts you can manouver it easily past the electrical cord bundle and get it out. Then to put the new one in, start on one side feeding it thru, in front of the subframe mount. Once the curved part is just beyond the subframe mount, press down on the subframe and pull the bar over, towards the front of the car. Now fish it down and then pull it over the subframe on the other side. Finally, to reinstall the subframe bolts, jam one of the interior bolts into position as you press towards the rear of the car on the subframe. Then do the same on the other side, only you should be able to actually get the bolt all the way thru and into position. Tighten it and then go back to the first one and actually get it in position and tighten it down. The outside ones are cake after that. They bolt right up.

I did it by myself. I'd say,including the time to remove the rear struts, this only took me about an hour. Not bad at all!!

Really, it's not as bad as it seems.

R

 

Woah! I put the rear sway setting on the forward hole...quick question...is it going to be ok there??? I mean, there is like a 1-2mm gap between the drop link and the spring. Seems MIGHTY close for my comfort. Just need some reassuring. Thanks!

R

 

Davbret, you might want to check that your sway bar is centered. Also, once you lower the car off of the jacks, the suspension will compress and there will be more clearance.

 

Ya, the bar is centered...there's about 1-2mm on each side before the stops. George took a look at the setup and said it was fine, nothing to worry about.

Let's just say that if there is something to worry about, I'll worry about it! I think me and HighAnxiety would get along good.

R