Not happy with my setup

[rxsleeper]

Take these suggestions with a grain of salt as I am by no means an expert.

A factory Z has no means to adjust camber. I use both the eccentrics in the lower control arms (front and rear) and camber plates. I do not remember what the FSM specs for alignment settings should be but I will give you what my settings are on a track only car.

First, heed the advice given above by the other ClassicZ members as some of them are experts, IMHO.

Poly bushings all around. Does this include the T/C rod? You may want to search around here or over at hybridz about the problems using poly on the T/C rod. FWIW, I use the old "Kontrolle" style delrin/aluminum on the T/C rod. The bushings are available from MSA.

Make sure your ride height is equal, or close to equal at the front and rear. Too much rake, front to rear, WILL change handling. Corner weigh the car, with you in it, and get it as close to balanced as you can. Then add 2.5 to 3.5 degrees negative camber in front and about 1 degree less in the rear. Set the front toe to 0 or at the most 1/32" toe out. For the the rear, try for 0" toe but it would be ok if you had just a little toe in, 1/32" or less if possible. The rear of a z will "squat" under acceleration and tend to toe out slightly.

Get as much caster as you can in the front. JohnC's suggestion is spot on.

Tires: use a low profile tire. I run 225x50x14 but the tires are not street legal.

Sway bars. I wouldn't change your bars until you try the other suggestions. Bigger front bar does not always translate into better turn in or handling.

Are your shocks adjustable for both rebound and compression? Some changes there can also effect how "crisp" the car will handle.

I hope this helps and hopefully some real experts will weigh in as well.

Good luck

[John Coffey]

I wonder why?

It that because of the differences in front end geometry?

Or because the rotational mass of an in-line six is greater than that of an in-line four? Both of which want to continue in their present direction of travel?

Or is it weight and wheel base related?

Tell us more.....

I honestly don't know but my guess is that the car has a lot of yaw inertia that's related to where the weight is in the car and accelerating the L6 engine mass takes a bit of time.

When I went to solid engine, trans, and diff mounts in my old racing 240Z, turn-in response was increased a bunch. I have also driven a SR20DET swapped 260Z on a race track and its turn-in response was good.

It may also be a feel issue that's caused by the driver sitting so close to the rear wheels.

[jmortensen]

I wonder why?

It that because of the differences in front end geometry?

My theory is that the Z has roughly parallel steering. Adding Ackermann (inside wheel turns more sharply than the outside wheel) should increase the turn in response a lot. I had a friend with a 510 that turned in OK, but wasn't anything to write home about. He bent his steer knuckles to get 100% Ackermann and the car was absolutely transformed. With no other changes it was super loose, damn near impossible to drive fast. Since the Z is front steer car (rack in front of crossmember), there isn't a whole hell of a lot to do to get more Ackermann. You can install longer steer knuckles, but that slows down the steering response. It's difficult and requires some welding/fabrication, but you can relocate the rack rearwards closer to the crossmember. That's what I did. I don't think I was able to get 100% Ackermann, but maybe 60 or 70%. Someday if I get the thing running I'll report back on how it worked out...

[five&dime]

Caen Fred.... I want to see larger pics of your car. I love it!!! Didn't see any photos of it in your gallery.

[gira]

Caen Fred,

Try in this order.

Get more caster. John is right, 5 degrees is pretty strong though. Make sure both sides are the same. To gain this caster, you will have to change the tc rod length.

Change the tires.

More camber is definitely needed for a high performance radial, both front and rear.

The miata has about the best suspension you can have on a race car. The double wishbone is unbeatable as far as geometry goes. When you lower a street z without changing other pickup locations the roll center goes down below the ground. This is another deal althogether. I am surprised that you only got this much negative camber from lowering. My recollection is that a lowered Z got in the -2 degree range withouth camber plates.

[John Coffey]

My theory is that the Z has roughly parallel steering. Adding Ackermann (inside wheel turns more sharply than the outside wheel) should increase the turn in response a lot.

Forgot about Ackermann. You're probably right. Using toe out to fake Ackermann works until the outside front tire gets loaded and then turn-in response fades and the car tends to understeer a bit.

[John Coffey]

John is right, 5 degrees is pretty strong though.

I ran 7 to 8 on the ROD along with 1/2" wheel spacers and 275 width tires. Yeah it scrubbed a bit but I had enough horsepower to not be concerned about that. My arms looked like Popeye's! :-)

[coop]

Hey John, I might dissagree with you a little bit on using that much caster. I experimented with adding more caster and found that the steering wheel forces became so great that the car was difficult to drive. You see, I was using so much arm strength to turn the wheel that finesse went out the window and I couldn't react fast enough to put the car where I wanted to. I suggest that caster be set close to stock. Then you can add or remove spacers/washers at the end of the TC rod to keep the car from pulling to one side and to get the feel you like. Back when I couldn't afford delrin TC bushings, I would grind down the stock rubber bushings and surround them with big washers and then torque them down real tight. This worked quite well if not great. I later graduated to delrin bushings and washers(which I now use as spares) and I now use spherical bushings which are very precise.

Edited January 7, 2009 by coop
spelling

[John Coffey]

Hey John, I might dissagree with you a little bit on using that much caster. I experimented with adding more caster and found that the steering wheel forces became so great that the car was difficult to drive. You see, I was using so much arm strength to turn the wheel that finesse went out the window and I couldn't react fast enough to put the car where I wanted to.

I was able to reduce the steering kickback and bumpsteer by relocating the inner LCA mounting point and running a bumpsteer spacer. This made the car easier to drive with that much caster. It still took some effort but it worked pretty well with how my car was setup.

I think in your car you were prevented by ITS rules from making the changes I did?

[Caen Fred]

[coop]

Right you are John. I'm not allowed to do that mod. Also, I've been told by folks behind me that I "throw the car into the turn" to establish my drift angle so I may be making up for weakness in the car's performance by driving it with less finesse than one might drive a really good handling car. I do feel that my car turns in quite well, maybe because I use the following technique on tight corners: I brake very hard right up to the turn in point, then quickly let off the brake and while the front end is still highly loaded, I make a sharp turn of the wheel to get the turn in and rotation I need. Then I use the throttle to adjust my track out. This was the only way I could get the welded rear end to work. I use a Quaife now so I presently can use a little more finesse. :laugh:

[John Coffey]

With a welded rear that's the style needed to get the car to turn in. Dirt tracking. That's basically why there's a setup difference between East Coast and West Coast 240Zs. East Coast guys tended to run LSDs that were setup with not a lot of preload. Us West Coast guys had no money and ran welded diffs so we needed more spring in and roll stiffness in the back to get the car to rotate.

With a Quaife, which is what I switched from a welded diff, you soften the rear a lot and move roll stiffness forward.