Figuring out correct Spring Rates

Sorry. I disagree to some of that statement. Yes you have to stiffen the suspension but more so in the rear. Mucho camber, as you say is not the answer. Too much camber limits traction and can actually decrease cornering due to limmited tire contact. On my ZX2-SR I run 2.5 degrees in the front and 1.5 on the rear and my Hoosiers wear more on the inside. Since the car is also driven on the street with stock settings I have not gone wild on stiffer springs. I am running the Eibach Pro Kit and the tokiko struts designed to go with the springs.this was the stock suspension on the SR. I have a 22mm Progress adjustable rear bar. The car handle really well.

Yes, rear roll stiffness is key. I was disagreeing with your statement that more front roll stiffness on a strut car will make more understeer - that is just not true in most cases. The normal Carroll Smith rules do not apply until a car has some semblance of a balanced suspension and a decent contact patch. When things are really out of whack, like a stock econobox, sometimes things become counter-intuitive.

Tire wear is not the end-all for camber decisions. Do you have a bunch of front toe-out? I bet you do, which will really chew the insides up.

I'd be willing to bet good money you'll improve mid-corner grip and lap times with more front camber. Walk around the grid at any ProSolo or Tour with a camber gauge and measure the strut cars - anyone with 2.5º will be maxed out on adjustment, and wanting more.

MX3,

It isn't simple. Suspension design/tuning and vehicle dynamics are quite a rabbit hole to jump into. I have been playing with this stuff for close to 15 years since I first got involved with Formula SAE. I don't have formal engineering training which makes it more difficult for me to get my head around some of this stuff. There are short cuts and rules of thumb that can get you closer to what you want. But short of copying what someone has done with the same car and same tires that works well, be prepared to spend a fair amount of time studying and experimenting.

I am the owner of the car Perry is talking about. The Motion Ratio is ~.80. The Spring angle is minimal. I corner weighted my current Mx-3 that has Ground Control Coilovers on it and the corner weights were: LF:831 RF:860 FR:545 RR:479 I have since raised both front coils one turn so I am sure that these numbers are slightly off.

What is the goal for matching the spring rates with weight of the corner. I think I am calculating right when I say that if we went with a 600 in lb springs in the front that every 384lbs would compress the spring 1 inch. I am ignoring angle right now but understand how to include it. Meaning that the car would settle around 2 inchs on its own weight. What do you shoot for?

MR = 0.8

MR^2 = .64

So 600lb springs = 600*.64 = 384lb/in at the wheel, like you said.

Unfortunately, there's not really a formula for spring rates (or rather, wheel rates) based on the weight of that corner.

Springs are used (in part) to keep the car from rolling in a corner, especially when the suspension geometry is less than ideal. If you have great camber curves you can go softer, if you lose camber dramatically with roll (most strut cars), you'll want to go stiffer. But of course, there are other factors - swaybars are the biggest. You can get away with softer springs if you have bigger bars, but they bring their own troubles.

Is this autocross only? Run as much spring as you can before the car gets skittish on the roughest surface you run. This number will be higher with better shocks. 100lb/in is a good step to raise them by as you experiment, 200 isn't unreasonable if time and money are short (when aren't they?)

The Springs that MazdaSpeed sells are Eibach coils that fit the Ground Control Coilovers. The options for the front are:425,450,650,700,950. I am currently running 375. I think that 650 sounds like the best option. I also track the car but I can always change back if these are too stiff for the track.

A spring does not resist compression evenly as you add weight. I snatched this quick description off another website:

What does "Linear Rate" mean? It's pretty simple. Let's say you have a 15 inch long 100 pound rated spring (and let's assume that it will coil bind - where the coils touch due to compression of the spring - at a compressed length of 5 inches). This means that it takes 100 pounds of force to compress the spring one inch. So, it will take another 100 pounds (for a total of 200 pounds) to compress the spring 2 inches - so on and so forth. If you graph it out, it's a nice straight line. You can see that our spring can take 1000 pounds (or 10 inches of compression distance) to collapse it to the point of coil bind.

Does this make sense?

BTW, that website has some other pretty good info. http://www.yellowdogracing.com/springs.htm

I usually run 0 toe and my tire temps show that I am right on the money. I run mostly track days with an occasional autocross thrown in.
Yes I have heard of some really wierd set ups, but do they really work better than the conventional set up ? As you have said, with the srut set up, lean and camber are related. the more lean the more camber is nec.