tube80z

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

There are a number of options I've used in the past. I bought a nice holesaw notcher and thought it was really good. Then I discovered you don't need a notcher at all and can simply cut two angles on the tube across the center line. And for really funcky angles you can use a program called tubemitre (search google for it) and then transfer the output to a tube and plasma the end off. But the big problem in all this is being able to measure the angle the tubes come together. Take the time to build a simple protractor for tubing and it will save a lot of time in the end. And for the computer geeks there's a program that calculates all the bends and gives you fishmouth diagrams. I believe it's called bend pack or similar. Cary

I won't argue that for most autox has little seat time. But it is racing and HPDE is not. Cary

Hey, at least you used search

A friend did this to a 510 racer years ago. It made virtually no difference to the car and he eventually went back to normal brakes. The only real advantage was people got all hot and bothered about it and it made it into the Japanese magazine Hero or something like that. Only downside is if you lose a half shaft you've lost a brake. Cary

I have a simplified spreadsheet I use. You can pick a target frequency and if you know your weights, sprung, unsprung, and all the weight transfer parameters you can work this out. Measuring the car is usually the most time consuming piece. With slicks we're currently very close to 3 Hz. With the radial atlantic tires we've found 550 springs work for a car in the 2200 pound range. Cary

I'm not a track guru but at hillclimbs, which are higher speeds and rougher courses I haven't had a problem with one inch of droop in the 400 to 500 pound spring range. I run less than that in the front. Cary

Do you ever get the idea they aren't listening to this? Cary

Target has a cheap philips dvp5140 player that is can be made region free. It will play NTSC, PAL, avi files, and a number of other things. $40 was what I paid on sale. I watch WRC videos on it all the time from the UK. http://www.amazon.com/review/product/B000F2KUK8/ref=dp_db_cm_cr_acr_txt?%5Fencoding=UTF8&showViewpoints=1

Because you were interested in the spring rate at the contact patch. My guess is Erik was doing calculations for wheel or axle percentages when setting the car up. Cool, I can't wait to see what you find. Cary

I used to do this all from calculation but I found a really cool method to do a direct measurement on the car. You need to remove the shocks (and what I've done is use a set of old modified stock struts with no oil). You put these in and then then lock the opposite end of the car. Then you bounce the end your interested in. Here's a video of the process in action (bounce test) http://www.racing-car-technology.com.au. What's cool about this process is you get friction effects included and can see how this changes with friction. For a direct measurement of motion ratio all you need to do is measure the change in strut shaft length as compress or extend the suspension. I have a bunch of quarter in AL chunks I use under the suspension to make the change. The ratio is not linear and if you're doing shock work that may make a difference. In general I've found a number of ways to measure the car directly and found this gives more realistic results than calculation. Billy Shope has some procedures based on Miliken's book using scales and a floor jack. You can read about them here, http://home.earthlink.net/~whshope/index.html Cary

It changes the motion ratio.