Springs Rates for Racing... Again

[boostedz]

I cannot give you much help on your problem but can point you to an individual that frequents hybridz.org, just do a search for johncoffey. Well known for his racing and hes speed shop.

He could definetly help you out.

[SuperDave]

Not that I'm as expert as the others who have replied, but (when has that stopped me before)...

Since you already have 350# springs on the front, and stiffer rear springs is one of the things that will help understeer, 285# springs would get you to SpudZ's 350-285 ARRC-winning spring rates.

You might think about getting some of the eccentric rear control arm bushings that would let you adjust your rear toe-in, which could also help your back end turn some.

PS - I'm about to get ready to prep and paint my ITS 240Z project and I'm thinking about painting it LIME GREEN much like yours.

[jjones-lg]

Kinda of an old thread but I can't believe you guys are running such light springs! I haven't raced my car since '95 but the Z and tires haven't changed that much. I started at 350 and worked up from there. I think we were over 600 in the front by the time we were done. That was on the 280 (I sold the 240) and we were running Koni shocks cause I knew the Tokico's wouldn't take the rates we were moving to.

We were running the Toyos (I got the first set of 225/50/14 of the boat in '93) and those things lie lots of camber and tire pressure. On the 240 Z for the Airport course at Holtville I was running over 6 degrees on the left side (mostly right turns). For Willow and Phoenix we'd back the camber off to 4 as I remember. I came from production car racing on slicks and was used to setting suspension by tire temps but found with the Tokico's we had better luck setting the camber by feel and tire wear.

The 240 and 280 were sensitive to different suspension settings, which was kind of weird. We were so dialed in on the 240 we would use different camber setting for different tracks. That car responded to camber setting more than sway bar adjustments once we got it dialed. The only thing I just couldn't resolve till I sold the car was the lifting of that inside wheel. I robbed the quick adjusting sway bar set up off the 240 for the 280 and had to build something different when I sold it. I theorized that softer springs and stiffer sway bars in the rear would control the front-end roll better and it worked.

We built the 280 for the 5 speed (ITS). My thought was on the faster tracks the extra gear and torque would make up for the 350 pounds. Once we got the brakes sorted out it proved to be accurate. I did a few different things on the 280 than the 240. After watching some videos we did it looked like some to the problems we were having even with the stiffer springs was body roll. I decided to play around with roll centers front and rear. I suspected the roll axis was too much lower than the roll center of the car. IT rules allowed for “any” struts so I made several sets of rears to move the roll center up. On the front I fabricated metal “bump steer” blocks and welded them on. The front is kinda of limited in what you can do and still clear the tire. Turns out that the rear roll center was fine but on the 280 I build some offset “bump steer” blocks to raise the front roll center. With the old Datsun 2000 I’d raced in the 80’s I found that when we got it lowered enough the roll center was way too low and what a difference when we finally got it right.

All I can say is if you don’t have camber plates on a racing Z you’re spending you time and money in the wrong places.

BTW I still have the 280. I probably should sell it but haven’t been able to bring myself to do it.