I have wondered about this for awhile and thought I'd ask around.
I see that some people like to buy a pre-packaged kit like the TVS from Hotchkis or PST or something similar, but I'm still curious about it.
When a person sets out to improve the handling of their car, their personal tastes will differ from the next guy. I'm interested in knowing how these engineers arrive at the specific parts that become part of the kit. For example, with engines, we expect the exhaust valve to be smaller than the intake valve because it always is. In the case of suspensions, the front roll stiffness or spring rate is always higher than the rear. I mean in terms of our front engine/rear drive cars.
I guess I am asking, is there a percentage of roll stiffness that they use to determine what to use? If the front is say...a *100, is the rear a *75? More at the rear causes oversteer, less will result in understeer?
Another hypothetical:
3500 lb 72 Duster with all iron 360, battery in trunk.
.92 Torsion bars 1.250 front sway bar KYB shocks.
Stock leafs with 1 additional leaf, .75 rear bar, KYB shocks.
I haven't been able to drive the car on the street yet for many reasons but I am just interested in the science of all of it. I don't want to just do what others did, I want to learn the math of it. Do people start off setting the car to lean/roll as little as possible while giving a decent ride, then fine tune the chassis with small changes?
I am interested in whatever anyone can spill on the subject.
Thanks, Jeff

Time to read

I have this

http://www.amazon.com/Build-Ultimate-Super-Street-Mopar/dp/B00538MYA8

For starters, the the whole bag of goodies Carroll Smith's Engineer to Win series

http://www.amazon.com/Engineer-Motorbooks-Workshop-Carroll-Smith/dp/0879381868

The MP oval and circle track books have some interesting information.

I own the car on the cover of the Ultimate Super Street Mopar. And that is a very good resource for information. Andy F's book in another and if you can find them, the old Direct Connection Circle/Oval track books have lots of stuff too. The Mopar Performance versions of those books are watered down and missing a lot of the information you are after.

Sorry Andy, forgot about your book

I agree, some time library time would be in order. I have read a plethora of books including those already mentioned. My takeaway, for the non engineer, the best book, bar none is:

http://www.amazon.com/Think-Fast-Racers-Why-To-Winning-ebook/dp/B00IJ2MB0I

One common thread thru out the book, which many newbies seem to ignore is, because they are looking for the holy grail, is, "everything effects everything else". You can't get around that as your set-up becomes more sorted out.

Andy's book gives an easy and simple answer for it all.

Another easy answer is simply set your car up to fall on the neutral handling line as shown below from the Mike Martin book, Mopar Suspensions.



Of course, getting front weight percentage is easy. Its all the calculations that go into figuring out roll couple front and rear that make it tricky. Martin's book gives info on how to do this, as do the other books listed above and the Mopar Chassis and Oval Track books also have info on it. Where it gets tricky is you can't just plug in rates. You have to find motion ratios of the sway bars front and rear and rear springs. T-bars are 1:1, so that part is easy. Once you have all this, then yes, its possible to set up a formula that show you where your car falls and then you can target the percentages on the chart above. I created one for my Challenger so I can see what changes may do to it, but I also have a configuration on my car that is different than stock using many non stock components, so it doesn't easily translate to other vehicles. I also set my calculator up to back into required leaf spring rates as these are the easiest part to customize. There are only so many t-bar and sway bar pieces out there, so we are limited on how wide a range of front end set ups we can get, whereas leaf spring can more readily be modified to match the front system.

The theoretical handling line is fine, for a starting point. But each driver has his idiosyncrasies which will make every setup a bit different even on otherwise identical examples.

This

The way engineers think about it is controlling the tire patch. The tires with the heaviest load are more likely to be overloaded than the tires with less load. On a nose heavy car the front tires take more load than rear tires. You can fix that by putting bigger tires up front but almost nobody does that since it looks weird.

The whole problem of handling for a nose heavy car then revolves around the question of how do you keep the front tires from being overloaded.

Some Mopar guys don't even like the 11.75 brake swap since it widens the front track width. But widening the front track width is exactly the right thing to do when you have a nose heavy car. If you aren't going to widen the front track width, and you aren't going to run big tires up front then you basically have a pretty car that isn't going to corner. The only other option is to spend a ton of money and turn your nose heavy Mopar into a lightweight race car with 50/50 weight distribution.

If you can achieve something close to 50/50 then your options open up. If you can move a little more weight to the rear and have a 55/45 car then you can have a pretty car that does corner. It might look like a 911 but it will have bigs and littles and will transfer weight to the rear on take off and maintain good weight distribution under heavy braking. Basically the perfect setup which is why the 911 has been killing it on the racetrack for many, many years.

The theory is one thing but a '72 Duster with a cast iron engine and stock suspension is such a horrible pig in terms of handling that theory doesn't apply.

If you want to learn handling theory then start with something nice and simple and square like an entry class pavement car. Something with a 50/50 weight distribution, rigid chassis and tuneable suspension at each corner. Then you can see what happens as you adjust spring rates, roll rates and shock valving.

A stock '72 Duster is a disaster and you have to stop the bleeding before you can even start to think about good handling. You need to add a bunch of roll stiffness just to keep the tires from folding over turning a corner. The stock tires are way too small for handling and the spring rate is way too soft. The weight distribution is horrible so it will never handle very good unless you spend money to take weight off the front.

So I'm not sure what answer you're looking for. If you want theory then there are plenty of books. If you want to make your Duster handle okay (like a new Honda Accord or something in that league) then ignore the theory and just call Firm Feel and do what they tell you do. If you want a daily driver where you can apply handling theory then sell the Duster and buy a used Z06 or something along those lines.

Is that graph posted earlier copied out of your copyrighted book, without your express written permission, and if you don't take prudent action to prevent this type of ,violation you risk it becoming public domain, and you know all this as lawyer, if I am correct? I know you are nice guy, but fair is fair.

If there is an exception, I'd like to know it, because there plenty of stuff I'd like to put up.

Thank you for clearing that up, thought it was posted originally without author notation, but the copyright issue still exists.

Get a grip JCC

Look up fair use exception

[censored] eyeroll

Doesn't apply here, IMO, maybe it grips yours.

Clear enough?

Dude, just click "ignore this user", you won't miss much.

Thanks, I will.

Thanks everyone. I have some reading to do!
Jeff