tube80z

The weak link is on purpose. This is what lets the motor exit out the bottom of you really stuff the car. Welding in the crossmember will make the front a lot stiffer but if you get in a serious accident the motor will be coming through the firewall. It's your choice. Cary

I think it depends on what you do with your car. John had good info below on what he did on an actual racing course versus what I do in SOLO II. The tube frame car will have an underground front roll center too. But the 1 inch below ground RC is on my unibody Z car. It has a cage that ties into the stuts. When I got the car it had above ground front roll center and some weird spring choices. It was fast but was hard to drive. I gave up trying to make a three wheeler work and decided to try some advice I'd seen on the FF underground about using spring rates that were some portion of corner rate. I started with 400 lb springs, AD inserts, and GC camber plates. The rest of the suspension is monoballs in front and the delrin bushings in the rear, altough I want to change that to monoballs too. Front roll bar is 15/16 and rear is 5/8. Nothing too out of the ordinary. I guess I do have one thing that is a little different. I droop limit the front suspension, which has a major effect on the roll center. I have tried up to 600 lb springs on this car and it seemed like a good direction to go. Part of the problem is I can't lower the car enough to isolate for the spring change to say that's exactly what it is (I'm assuming people know that you have to change ride height to isolate spring changes). A lot of this will depend on tires too as you have to take into account their spring rate to determine the actual wheel rate. The one thing I do a lot of is change chassis rake to balance the car. And this does change the roll couple. So I agree that it has a major influence on your car. So we are in definite agreement that this is a key tuning tool. I just happen to play in a different speed range with my toy. Hence my advice is for SOLO II. I'm just offering it as something to think about. So what are normal Z spring rates these days? Cary "who only wishes he could afford to play on real tracks"

Good info. For what's it worth my car rarely gets over 80 MPH and never in a corner. At most course I run the average apex speed is 45 MPH or less. Which may be why I like this. Cary

Okay, I was a little harsh on that one. But you can get all this for a lot less in other books. It's still a good one to have but it doesn't need to be one of the first purchased. Cary

Lengthening the control arms is a good thing. Remember the TC rods and tie-rods too. Cary

I think Race Car Vehicle Dynamics is a great book, but it really doesn't tell you anything about struts other than give you basic definitions and tell you they suck. Before I bought that I'd look at some more basic books like Staniforth's Race and Rally sourcebook or Haney's book on tires. Those at least have some useful info for the DIYer trying to make their car go faster. Cary

The reply on RCs had a lot of good info in it. I think you can't go wrong with that advice. Some other rules of thumb to help you set things up: Scrub -- no more than 20 percent wheel width or tire width (which ever is bigger). For a ten inch wheel that's 2 inches (and ideally you want less). Caster -- one half the measured steering axis inclination trail -- around 3/4 to half an inch RC lateral migration (20 percent of track width) Vertical migration -- make sure it doesn't cross ground level in any real world condition. If this happens in a corner the car will momentarily lose traction. This often feels like a sideways hop and can be very unnerving. In general you want to run an RC that is close to the ground with the front slightly lower than the rear. Low is somewhere in the neighborhood of less than 5 inches off the ground. It depends a lot on the rest of your setup. High RCs will lead to large jacking forces, which is like a big lever trying to turn the car over as you enter a corner. They manifest themselves as a lifting that increases with corner force. Old triumphs, volkswagens, and corvairs had swing axles that were notorious for this. Just remember that everything is interconnected to the strut on these cars. You can't make on thing perfect without really screwing something else up. It's all a matter of coming up with the best compromise. Good luck, Cary

There's some good advice from John. I would also recommend that whenever you do this you spray weldthru (3M product) on the area to be welded. This is a very important step in making sure you keep rust away. One good point about seem welding that hasn't been mentioned is that if you ever wreck you car it is much easier to pull the parts back out. If you have simple spot welds they will often pop when you try and do this. I would recommend seam welding on any car the will see a V8 or hard use. Many times the spot welds will not all be holding on our older cars. This helps to ensure that the panels are all glued together. Cary

I have the GC AD inserts and I'nm generally happy with them. The bump adjuster as three positions but it makes little difference which position you use. There's just not much adjustment. The rebound is very adjustable and this what I spend the most time messing with. Given your location I would recommend a set of Konis or similar with the digressive valving. I think being able to get parts in a timely manner would be very good. A local shock expert told me that Koni's would have been cheaper than what I paid for the AD inserts but provided no real details. So you have a lukewarm recommendation from me. They do work, there's little bump adjustment, and parts are hard to get if you need them. otherwise they do work well and will allow you to run proper spring rates for a racing Z. Cary

Actually you want the control arms to be very near level to work best. This will help to reduce the jacking forces and scrub the tires less. If you want to adjust camber it's best to add it statically as you can't really get much back from the suspension without compromising other items worse. Cary