How 'bout this for a race setup?

[sopwith21]

Greetings. A newbie here.

Got a '74 260z that races on a 2-mile road course. Average speeds are around 75 mph. Slows to 35 and tops out at 120 or so.

The suspension was stock and I'm upgrading all four corners to Pro Shock coil over kits with Tokico adjustable struts, Pro Shock springs (350 fr/250 rear) and ArizonaZcar monoball camber plates all around. I know we can debate specific spring rates and strut brands all day, but won't this get me in the ball park and build enough adjustability into the suspension to have a decent base to work from? Right now it handles like a dog. Many thanks.

[240ZX]

Stephen, There are as you know many things to address while setting up suspension for competition. One item you may want to investigate and do is to replace all your old rubber bushings with polyurethane. You will be quite surprised with this improvement. Also, what about your tire/wheel setup...another biggy! Brakes, coilovers, tubular adjustable transverse links, etc., etc., the list goes on and on. But depending on what class you run, rules will dictate what you can and can't do.....check them first. Anyway, hope this helps some and wecome to ONE GREAT Z SITE.

[gramercyjam]

What do you mean it handles like a dog? What is it doing or not doing? Be as specific as possible.

What's your alignment settings like? What tires? Their age? Tire pressures? LSD? What about sway bars? Are the tokicos blown? I'm not sure Tokicos can handle 250# springs very well. Most setups use the stiffer springs in the rear as well. I never tried it so I don't know how well it works in reverse.

[260DET]

Has it got a tied in roll cage? Makes a hell of a difference, the stock 240 body is very flexy so diverting suspension settings and loads. 350f/250r sounds a very peculiar spring setup, they should be much closer tending to a bit more on the rear than front, but debatable Dump the Tokico's, Koni's or Bilstein's minimum.

[sopwith21]

It runs in a GT class so we can do whatever we like to the car. I didn't build the car and can't answer all your questions, but here's my best shot:

Yes, it has a tied in roll cage. Hoosier R45 slicks on 23x9x15 wheels, bought this year with approx. 80 laps on them, 20 lbs all around. Stocks brakes... insufficient, but will have to do until the chassis is turning. Sway bars fr and rear, don't have bar sizes yet. Stock four speed tranny, welded and locked rear end.

Previous owner had been running stock suspension set up. Believe it or not, the car actually handled halfway decent until the fr springs collapsed, necessitating the current revamp. The car understeers horribly all the way through the corner now. Unhooking the rear sway bar made it push going in and through the center and come out loose. A disaster either way.

For financial reasons, I must fix one thing at a time... that means the rear end, brakes, etc., must wait for another conversation. Right now I have to make it turn. The bushings are a good suggestion and I'm open to more. Thanks for all yr thoughts.

[sopwith21]

PS - any suggestions on exactly where to buy good poly bushings for the best price?

[2ManyZs]

With a locked rear, you have way to much front spring, that I can say for sure. Locked rears will increase the understeer considerably, and with the 350 front springs, it's gotta be pretty bad.

With what you have right now, I'd suggest buying a pair of 275-300lb springs and put them in the rear, and put the 250lb springs up front, then tinker with sway bar sizes to fine tune the handling.

[gramercyjam]

It sounds like you need to soften the front. If your bushings are stock, do those. I've used both Gmachine and others. I really don't have a preference. They all work for me. Also, I would first try switching the rear springs to the front and if you got an extra $100, switch to a pair of 275# springs for the rear. See how that works for you and go from there. If the tokicos aren't blown, I would wait on the decision to replace them until you test the other changes. Also, Hoosiers start out very grippy but don't stay grippy long. At 80 laps, they could be gone. It is hard to judge that though if you haven't driven on a freshly scrubbed in set before. Check camber and toe in. That makes a big difference. You shouldn't have more than a couple of degrees of neg. camber to start with. Go from there to adjust for tire wear and grip. Also, I like 0 toe to a hair of toe in. It does affect turn-in significantly. I like a little toe out better, but the steering effort goes off the charts with grippy hoosiers. you can play with that to see what you like.

[260DET]

With a dedicated race car like that with a strengthened body if the track is not too bumpy you could go up to around 500 lb springs, a bit lighter in the front than the back. With those sorts of rates you may find that you can do without a rear anti sway bar.

My car which has to be driven on the road has 275f/300r, its the Koni shocks which make such a difference, my teeth are in no danger of being jarred loose either. Tokico's, pfffttt :dead:

[dspillman]

HI Sopwith21,

I'll throw out one more combo....72 240z SCCA ITS

I've ran F/R spring rates 400/300, 375/300, 350/300 , Last year I settled down with 400/300 koni D/As, without R sway bar, front bar about 1", quaife diff. zero rear toe, 1/8 toe in front....... Handles fairly neutral.

I to have heard the reverse combo of heavier springs in rear, but haven't tried..."Mine works" for me. YMMV....

BTW...Keep a eye on your Link Mount Brace..."they help locate the rear of control arms". I just noticed mine were tearing, or breaking at bolt holes where they attach to the body .....lots of over steer... :surprised

Waiting for next race weekend.....

David Spillman

[gramercyjam]

I might have misread your initial post sopwith21. I was thinking you had already made the suspension changes and it still handled badly. If you havent bought those springs and shocks yet, you consider many dedicated racers use quite high spring rates, and the tokicos aren't valved for those extreme spring rates. Something to consider. I didn't know about the koni 8610 option when I bought my tokicos. I don't know anybody that has gotten the tokico illuminas custom vavled for high spring rates.

I know there are 2 schools on which end to put the softer springs. Both schools seem to work so I imagine that once you have made your choice, you can tune either to work well. My suspension setup is in about it's 4th iteration since I started developing the car and if the past is any indicator of the future, it will continue to change as the development progesses. I have heard about 300# springs is about as high as you can go with them. I'm running tokicos with 300# springs on both ends (contrary to popular opinion it seems to work at the level I'm at. You can spend a small fortune on shocks and such, but I'm not sure I want to go there with this car) and I don't have any complaints so far but my experience with my setup is low speed autox and a little high speed time trial driving so ymmv. (I may have a little push with that setup but it has been so long since I had new sticky tires I can't really recall. ) I don't run a full cage and that makes a difference what springs you might use too.

I know a very experienced driver with 400# springs on both ends and a full cage and he is very happy with his setup too.

[panchovisa]

John, the comment about 300# springs leads me to question if that is the wheel rate (including sway bar rate) or just the spring rate alone.

If it is just the spring alone then what rate are people using for a sway bar? Remember that every 1" front sway bar doesn't give the same rate (the length of "arm", material, rod end or polyurethean bushed drop links, flat ends on arm vs cross holes vs clamps, etc.).

The spring rate alone will affect brake dive, squat, and two wheel bumps. The wheel rate will affect cornering, turn in, and trail braking.

Pancho

(didn't get package sent until last Friday, sorry)