If one has a 3 link/coil-over suspension in the rear with a panhard bar, there is the opportunity to set the rear roll center height by moving the panhard bar up or down. The roll center height would be at the same height as the bar if one has horizontal, non-converging lower control arms.

With a leaf spring suspension the roll center height is found by drawing a line from the front spring eye to the upper shackle and noting where that line crosses a perpindicular dropped through the axle centerline. This height turns out to be at or a bit above the height of the axle itself, which would make it 13+ inches.

I read some thread that implied that one would want to make the roll center height the same front and rear, which means that a value closer to 10" is desirable. However, with a center of gravity at about camshaft height, a lower roll center height would allow more body lean, which is not a desirable thing.

My question is why wouldn't one just mimic roll center height of the original leaf spring suspension?

Ed

Ed,

Maybe David will pop in here and help....

And you might post your question over at www.pro-touring.com (http://www.pro-touring.com) for help over there too b/c they are way into modified suspensions..

pdq67

Ed,
Good question.
A couple of things Ive seen a fiew times when reading the books is to keep the front and rear roll center heights the SAME DISTANCE from the center of mass height of each end of the car.

As you have probably read, there is a "Mass Centroid Axis" (MCA) line thru the F/R axis of the car, the engine is a heavy mass so the MCA in front is brought low, the center of the car is higher with the tall roof so the MCA is higher there, the rear is pretty high also since the heavy rear axle and half the springs and shocks are unsprung weight and don't count.

All this brings me to agree that the rear RCH should be higher than the front, probably somewhere around the bottom of the Differential. I would guess the 13" height, or center of axle is the highest you'd want to have it. The lower the rear RCH, the more cornering loads are sent through the springs or anti-roll bars, so a lower rear roll center with no other changes will make the rear suspension act softer in roll. You will probably need to stiffen the rear anti-roll bar to make up for it.

I took a quick look at my Adams book but didn't find a rear RCH recomendation.