coilover and caster help!

[Dan Juday]

John, what is it that actually happens that ruins the handling when the lower control arms start pointing up?

 

In the front we can relocate the pivot points higher on the crossmember. The rear is a much bigger challenge.

[johnc]

Without getting into a big dissertation about instant centers and roll centers (refer to Chapter 17 of Race Car Vehicle Dynamics by the Millikens) what happens when the LCAs point up on the front and rear suspensions of the 240Z is that you get large amounts of tire scrub (lateral movement of the tire relative to the ground). Any vertical suspension movement introduces lateral movement in the tire and changes the slip angle. With constant slip angle changes from all 4 tires the car is being disturbed; it feels "skatey" and doesn't take a "bite" in the corner. As a driver you constantly have to correct with the steering wheel and it feels like alternate ends of the car are about to let go when driving at 10/10ths.

 

Its best to have the LCAs point slightly down at static ride height with a typical load on the vehicle. In the case of the 240Z, lower is not better.

 

Look at the picture below of the ROD at Thunderhill with the left suspension fully compressed in a fast right hand turn:

 

 

Even at full compression the car still has about 4" of ride height measured at the rocker panels. It was set up with 6.5" ride height in front (measured at the front of the rocker) and 6.75" ride height (measured at the rear of the rocker). That was with 25.2" tall tires, and 27mm bumpsteer spacers. Even if I relocated the front LCAs I would have been stuck at that ride height because I couldn't lower the rear any more. .5" of rake is about the most you want in a 240Z and still keep the handling neutral.

[majik16106]

well, ive got the 17x10, 275/40 on the tire, and i plan on using the imsa flares, which should be plenty big enough. i may have been a bit misleading, im not trying to put the bottom of lip a half inch off the ground, really as far as styling is concerned, i want the fender gap gone, with the 3inch piping on the exhaust, i really cant afford to put the bottom that close to the ground anyway, as this is a street driven car. if u look at the pics i posted in my other thread, there is a good almost 2 inches of gap. anyway, thanks for ur help, ill figure something out i guess.