tube80z

Attached are some pics or our interpretation of the new rear control arm. These were built out pf parts recycled from the previous control arm thread that Jon started where rod ends replaced the outer rubber bushings. Two things were immediately apparent when putting these on. It was much easier to get them bolted up and the strut aligned with the camber plate with no fuss. It was one of those why didn't we do this a long time ago moments. And I should also mention that aligning for rear toe is now very simple. These are mounted on the back of Dave Kipperman's LS2 powered autox car. We gave them a bunch of abuse this past weekend with no issues attributed to the arms. We had a record heat wave move through our area so any plans for a back to back comparison were thrown out and at this point we're probably not motivated enough to revisit. Cary

How much did you get that setup for?

We spray tires at an autox to get the tread temp down to a range that produces grip. If they get too hot they get greasy and your lap times get much worse. I haven't ran on recent kumhos but they used to be worthless much over 110 degrees of temp measured in the pits. Unlike road racing the generates core temperature in a tire autox heats from the outside in. If you read a lot of tire data they'll tell you that you should see temps in the 190 to 200 range, which leads to this confusion. If you ever see a temp like that on an autox tire bits of rubber would probably be flying off.

When you figure 1.5/1.6 Gs for transients you'd be close to 2.5 degrees and that doesn't take into account tire deflection. So that's about what I'd expect to see. It does look like more camber could be used but I'd check temps to see how they look first. More camber will help in turns but you may lose too much braking for it to translate to a laptime decrease. Your picture is good but it's hard to tell how much the inside is jacking up (if at all). I've found in the past that sometimes I can't control roll as much as I'd like with bars and spring when the inside of the car lifts up. This is where a droop limiter can help to reduce roll. While it will reduce the lateral contribution of the tire that's limited keeping the outside tire flatter do to reduced roll may give you a net gain. And limiters are a lot quicker to add then longer lower control arms. It will also make the car change direction quicker in transitions. Just a thought, Cary

The slicks will last a lot longer if you flip them on the wheels and rotate often. I do two events (Fri, Sat, Sun) on a set before flipping. I use two sets of wheels to do this. Friday I will run in the Sunday tires. Saturday I will run the practice set. If done right I get a new set of used tires that are added to this each year and the 4 worst tires are removed. For the bias ply slicks I match them by diameter. Tires are bagged after each event and treated with formula V following the directions.

The new B compound is supposed to be the same as the what the A6 uses and I've been told negates this advantage. You still have the radial versus bias ply thing and so far I've found radials quicker. How long it will take Hoosier to get radials into all the slick sizes has yet to be seen. Given your soft spring rates you will probably be better with A6 hoosiers or using the kumho 710s. The slicks need to be worked pretty hard to get heat into them and make them function. The Atlantic tires even more so. So keep that in mind when you read "our" tire advice.

How far forward do you sit in the car? My attachment points are under the seat. Cary

A friend had a car similar to yours but LS-1 powered. It was probably 350 WHP and similar torque. 17x12 kumhos in back with 425 front spring, 400 rear, and similar bars. Very neutral and it's strength was how it could squirt out of corners. The one issue this car had was it worked the rear tires pretty hard and this was from the rear roll center being too high in my opinion. I think if that was fixed it would have been much better. The FP and XP cars we running all are currently at least 550 all round or higher. We're using FA tires rather than cantilevers. We have two cars currently running V8s with over 300 WTQ and they put the power down in corners and have excellent straight line traction. There are others on this forum with big HP/TQ and similar setups (Clifton comes to mind). It seems from an earlier thread you mentioned you had 250 springs in the back. When I first got my car it was setup like this all the stiffness in the front and very soft in the back (PO stated what you describe). The car was very adept at three wheeling on corners. Running a more balanced setup fixed this and the car was much faster. If you know you're corner weights try springs that give a wheel rate of about 0.8 times the corner weight. That seems a good rule of thumb for the street radials. On slicks we're trying to be closer to 1 and I hope to experiment with higher rates this summer. Hope this helps, I'm happy to tell you all the settings on our cars. Cary

Technically yes, practically no. What I mean by that is you can jack up one side of the car and the spring will come completely unseated. With the limiters this isn't allowed and there's a small amount of pre-load still left on it.

Maybe they'll chime in but my experience was a ten inch rim gave up too much on these tires. And watching one of the locals run them you could see the tread move before the car would ever start to turn. Are you sure they aren't running the GT-2 radials that are a similar size?

You have something else wrong with your car. We run stiffer than what you're talking about and have no issues with straight line traction or oversteer. And this is with cars with big torque too. Cary

We're using them all. Jeff (white and blue) and myself are on 13 inch bias ply hoosiers, the Chandlers (light blue custom bodywork are running 15 inch hoosier bias plies), Morgan (red and yellow cars) is mostly on 15 inch GY radials, and Dave (grey and black) is running yoko radials. Past testing on a L6 powered car indicated the GY radials were quickest. The yokos are a medium compound and take a while to heat up and may work better in the heat we'll get this summer. We plan to do a big tire test this summer and see how it works between a few cars. We chose the slicks because they are easy to find used and cheap. The atlantic tires are very light and heat up quick, which is good for autox. The new hoosiers are now all using compounds similar to the A6 radial street cars (designated B compound). Supposedly in response to crappy performance on the nationals "dune" course. You can run the fronts all round but can't do the same with the rears. And when buying used you need to be careful to get fronts and not rears in similar sizes as they won't turn very well. By going with the same size tire all round you'll lose half to three quarters a second on a 45 to 50 second course. At least that's been our experience. The larger rears allow much earlier throttle application while still maintaining a lot of cornering force. Gives a whole new meaning to point and squirt. We have a tire management routine for the slicks that lets us run them to the cords with decent performance. We use formula V tire treatment and bag the tires between events. The performance drop we see is a lot less than our buddies running the kumhos and hoosier radial street tires, of which hoosier seems to fair worse. The yellow car above is my old car and ran front and rear limiters. Currently it only has rear installed. You'll find using the limiters will make the car react quicker. It will be similar to when you jumped spring rates. Also keep in mind you need to go stiffer to make the atlantics work if you chose to o down the route. All our cars are running at least 500 lb-in springs. And a few of the heavier V8 cars will probably be going up to the 650 to 700 range this year. Cary

You've gotten a lot of advice in the thread but there are a couple of areas that haven't been mentioned. How calibrated is your right foot? Still L6 or V8. Why I ask is that the first time I drove friends similar car I had very similar issues. I chose to go a gear higher and found that worked for me. You have to remember that the LS1 has about twice the torque of an L6. With your really soft springs when you step on the gas it's going to use a lot of travel. Are you bottoming (use zip ties to see). Pictures of video of the car in action will help a lot too. Some of the power on oversteer could be the rear squatting and the nose raising. Check your tires. Have you cooked the centers out of them. Big power can do this pretty quickly if you're not careful. Handling will become evil with the centers gone. Good luck, I personally feel your car is too soft to make this combo work. Cary

We have six local cars all running formula atlantic tires. Two are on 13s and 4 are on 15s. Here's a few pics from our last event (my car is currently not running). As you can see there's a lot of variation on how the cars are using their tires. We'll use this to make changes to try and get the tires in a better orientation to the ground, which will usually make the car faster. One thing to keep in mind when looking at all this data is that you'll need to compromise in the real world. Our low buck acquisition system is a camera, stop watch, radar gun, pyrometer, and driver feedback. We look at the data and the lap times and then look at the pics to see if the car looks good or has obvious problems. We often see that the tires are struggling to maintain a good orientation to the road but often find that when we get this right the lap times may suffer (less braking or drive off the corner). Looking at pyrometer data most of the tires (hoosier, GY, yokohama) all will run about ten degrees hotter on the inside when they are working well. It was looking at pics like this that lead to using droop limiters to try and keep the car jacking up and lifting the inside of the tire off the ground. In these pics only the yellow car is running limiters. Look at it's tires compared to the others. Sometimes crutches work Cary

Hmm, is that project Z0Z?

The large area that sits in front of the tranny is going to be a problem. That looks like it's going to interfere with the seats. There's precious little room in that area of a Z as is. That's the one big item that may nix this mod. Cary

I haven't had a chance to look too closely but I can offer some educated guesses. The leaf spring is lighter than steel coils, it may not offer any resistance to roll in how it's mounted (letting the engineers seperate vertical rate from roll rate), and it won't add bending forces to the shocks like a coil over solution. Not sure if any or all of these were criteria. Cary

I really like the analysis you did and I think that will really help to get you into the ballpark. The next step, which maybe should be a new thread, is now how do you tune this at the track. There are a couple of things to keep in mind. Your car should be generating 1.3 to 1.5 gs of lateral acceleration and the tire will deform a good amount (see photo below). What I've found is that you actually need more camber than just upright for max grip. Each tire will be a little different and you'll need to experiment to find that window. Cary

I have a friend that has the 240SX rears with stock fronts and 4-piston toyota calipers with good pads. We ran the car at several autoxes and it had completely rebuilt stock brakes that we on good shape. Then we changed over to this setup and there was a noticeable difference. We could brake deeper into corners and the brakes were very consistent. The balance for this setup on his car was very good. So in this case it was much better than the stock setup. I will add that the kit he got from MM didn't have any info about needing to change brake lines to make it work. We figured that out when we got into it. A quick search here seems to indicate that it's been a known issue for some time. So be warned. Hope this helps, Cary

So you can't use the trick of a lug nut for a mag wheel? Normally that replaces the spacer shown and makes everything go together easier. Cary

It took me about three events before I started to really like the stiffer setup. After about a year you'll jump in someone elses car and be shocked at how slow to respond it is. Are you sure? Why I ask is if you didn't actually measure you're springs you'll find that they are often off when you measure rate and free length. You may be able to swap around what you have to get things closer. I'm not sure unless you have a lot of development on the car and a really top caliber driver that this will make much of a difference. It gets even more complicated when you start thinking about tire rates too, which vary with speed, temperature, and pressure. Glad to hear you had good results with this. Another convert to the dark side?

I'm not sure this will help or not. I used to have an FIA approved recaro or sparco (I can't recall) and it was composite of some form, probably a high end fiberglass. I can't say the seat was very comfortable at all but looked cool. I think the deal with FIA tests is that it's gone through a specific level of testing and from what I can gleam FIA doesn't like seat back braces. So a lot of the FIA seats are intended for bottom mount only. I currently have a kirkey aluminum seat and I like it much better. I can mount it lower and farther back into the car than the previous seat. There are a number of expensive upgrades that you can buy for these to get halo and additional thigh support. Or if you're handy at fabricating you should be able to do it yourself and save a lot. I don't think this seat has any certification that I can tell. Maybe some of the newer seats do but you'll pay for it. It's comfortable enough with the padded insert but can easily be customized to fit you if you use a pour in bead liner (preferred over the foam). This would you give you a form fitting seat and excellent absorption. This is very commonly done in the formula car and sports racer arenas. Hope that helps, Cary

Since you're in Bend you should check out the autox club of central oregon. Their events are at the fairgrounds in Redmond. Go to http://www.autoxclub.org/ for details and schedule. I will be running a lot of their schedule this year with Paul's old car running with V8 power. Morgan Smith has a 350 chevy in his Z and Dave Kipperman will probably come play at a few events with his new donovan engined car. Cary

Do these cars use bushing compliance to control toe? I know some of the new mulit-link systems use rubber bushings that are very stiff in certain directions and compliant in others. It may be something as simple as that. For a test I'd take the wheel off and mount a long bar to the hub and lever it back and forth and see how much it moves. Then try the other side. It may help to pin point the issue. Cary

I've been looking for that every time I go there. So far nada. One of these days ... Cary