Katmans ITS suspension set up information
 

Hey all,
Ketih Thomas aka Katman posted this to the Improved Touring list and is allowing us to post it here. Thanks Keith !!!


" The basic difference between my novice (less than 2 full seasons) setup and what happens later is spring rate (and whatever corresponding shock changes need to happen, obviously). I like to start them out softer rather than stiffer because I believe it helps them reacclimate to the car quicker during the course of a weekend (remember, we're only driving these things once a month or so) so they're up to their potential sooner. Softer is generally less twitchy (which 240Z's have an abundance of to start with) and easier to stay on top of until such time that the gluteus maximus becomes a finely honed and worthy sensing instrument. Plus, off roading is easier on the unibody with soft springs.

My progression on springs goes something like (front/rear) 285/240, 325/275, 350/285, and finally 400/350. The 350/285 and the 400/350 each won an ARRC. For whatever reason the west coast seems to run in the 250/275 neighborhood as I recall. I don't know if that's because the tracks are bumpier or what. Me thinks those running bigger spring in the back than the front are either in the 6 inch ride height neighborhood or aren't really driving that hard. Also, lots of folks run ungodly big sway bars, like 1+ inch front and 3/4-7/8 rear, which really distorts what the springs should really be (personally I don't like how bars wanker the chassis so I prefer to balance with springs and trim with small bars). I've also come to the conclusion, correct or not, that the spring rates you need to achieve comfortable front/rear balance are very sensitive to roll center. The lower the car gets the more the front roll center heads toward China and the more spring we need to overcome the roll leverage that results. Anyway, be prepared to own a good collection of springs. Ride heights at the rocker around 5-1/8 to 5-1/4, cold with driver.

Here's my preference for things not so varied. Rear toe: I believe in the low drag setup, zero or at most 1/32 total toe in. I refuse to correct bad handling at the back by dragging the tires around. At the front I used to like 1/32 to 1/16 in, but to overcome persistent low speed corner entry problems we eventually settled on 1/8 total toe out. If I can get away with less for some tracks I do (again, low drag), and I begin to squeal when I start needing over 3/32 total out to get it to turn in.

Camber for the Hoosiers is in the 2.5-3.5 front and 1.5-2.5 rear neighborhood. I quit being anal about measuring camber because I tune with the pyrometer, for better or worse, and near the end we weren't visiting many different tracks. When properly measured and repeatable (i.e. I never change the camber unless for two sessions in a row I get the same answer), I like about 20 degrees hotter on the inside than the outside (and I won't be too bothered by 25). With the old bias ply's I shot for almost no bias but that's another kettle o' fish.

Sway bars: Like I said, in the SE the tracks are pretty smooth so I can get my balance with spring. If you have lumpy tracks and need more roll control than you can get with the springs because you got potholes to contend with then you're out of my realm of expertise. We ran a front bar equivalent to a 15/16 solid with one end of the end links mounted in poly so it was somewhat adjustable by preloading the poly- so its torsion rate was probably closer to a 3/4 solid. Our bar was something I made along the factory shape but in a 4130 tube (heat treated to a Rc=63), which only wighed a few pounds. Nicest part I ever made. I miss that bar.....

Shocks will eventually be very important. When the overall understeer/oversteer balance is achieved with the springs and bars for sweeping smooth turns, everything else is tuned with shocks (tire longevity, transitional handling differences between high speed and low speed turns, daily changes to the track affecting one end of the car or another, transitional differences between entry and exit, blah blah). I doubt the Illumina's will be enough shock (I'd revalve a Bilstein since the rule change outlawed my real shocks if it was still my problem)if you get over the 250lb/in spring zone. If the average tire temps from each corner vary more than about 20 degrees you may not have enough shock. That's a provocative statement (i.e. most people would blame the difference on the fact that there's more right turns than left, of the spring balance is off, etc.) I'll address later.

Corner weights- put everything on the right side of the car you're allowed to move, including the driver (our seat was offset 1.5 inches to the center from stock). A very good "with driver" distribution with a mid race fuel load would be 648LF, 625RF, 598LR, 580RR. Heck, that's EXTREMELY good for with driver.

A 240Z can be a handful for a novice. The back end loves to dance around under braking, and most of the time stomping on the gas when you don't want to will save you. Rotsa Ruck.

Find me off line when you get to the point where she's catching the brakes on fire. Or is that just an east coast problem?

Cold air intake, have to save that one for Monday.

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katman "

Enjoy Mike