In order to make your car handle you have to really understand the dynamics of your suspension and chassis geometry.
Overall
Take a look at your chassis as a whole. When you jack up your front drivers side wheel, does the rear drivers side wheel come up too or does your frame twist and the rear wheel stays planted on the ground? This is a good way to tell how firm of a chassis you are dealing with. The Focus chassis is very strong- when I jack up my car, the frame hardly twists at all. If your frame twists a lot, one thing you can do to stiffen it is frame connectors. A frame connector connects the front and rear subframes, almost turning your car into a full-framed vehicle. However, this is a last resort for people who only intend to race. Frame connectors are generally not needed for a FWD street car.
Front Suspension
Now take a look at your front suspension and frame. I'm assuming your car has a front suspension with struts since thats what most cars have. Are you running a performance strut or not? A performance strut will be firmer than a stock one, which means it won't compress as easily, giving you better handling around the corners. Some struts are adjustable. This is especially handly for dialing in your suspension, which I will get to later.
Take a look at the spring on your strut. Is the spring a progressive type or not? A progressive spring will have shorter, closer coils on top than on the bottom. This means that as the spring compresses, it gets even firmer, as opposed to a non-progressive spring, which will have about the same rate all through its compression. This allows the car to have a nice, smooth ride when driving normally, and yet hug the corners like a bear when driven aggressively.
Now take a look above your strut. A strut tower brace can really help prevent chassis flex in cornering. Do you have a tower brace? Is it solid? To find out how solid a strut brace is, look at it. It should be welded together, or at least double bolted. Single-bolted strut braces allow almost as much flex as no brace at all, therefore defeating the purpose of the brace.
Now get under the car. Do you have a sway bar? A sway bar will connect both sides of the suspension, keeping them in line and making it even more solid. The bigger, the better in this case.
Rear Suspension
The most important part of tuning a rear suspension is YOU. You have to determine how you want your car to handle, which is why I strongly recommend adjustable shocks (or struts). Follow the directions below to dertermine how you should tune your suspension.
How to promote oversteer (rear wheel drift)
Ever spun out, or felt the back of your car break loose around a turn? That's called oversteer. To promote oversteer (which most FWD cars want to do) you need to go with a much firmer rear suspension compared to the front.
A rear sway bar and shock (strut) tower brace are necessary in this case, as you want the rear suspension to be as stiff as possible. You want to get progressive springs, but firmer or as firm as the fronts. Also, the rear should not be as low as the front. Keep the rear up about 3/4" to keep more weight on the front of the car. The tricky part is the shocks (struts). The reason I reccomend an adjustbale REAR set is because you can really set your cars handling with it. Go with a harder setting for more oversteer, and a softer setting for less.
How to promote understeer (front wheel drift)
Ever been going around a corner really fast, and the car just plowed ahead and didn't want to turn? That's called understeer. Most FWD cars naturally have understeer because the power is placed on them during acceleration.
If understeer is what you're after, you'll want to get a front sway bar and strut tower brace, to keep the suspension all in line. Progressive springs are a must, and you want them to be just as firm (or firmer) as the rears. This will put more weight towards the rear of the car, and more force on the rear tires, keeping them on the ground. Adjustable shocks (struts) are still a must for fine tuning your suspension. Go firmer in back for more oversteer and softer for less.
Ride Height
This makes a huge difference in your car's handling when other suspension mods are done. An even ride height will be neutral, and will promote whichever type of handling you care to adjust it for. Having your rear higher will give more oversteer, and having your front higher will give you more understeer.
Weight Distriubution
This also makes a big difference once mods are done. Ideally, your car would have a 50/50 weight distribution. But we all know that's not true. Most of our car's weight is on the front wheels. To get your best handling, try doing small things to transfer weight towards the back. Move your battery to the trunk, and remove weight wherever possible from the front.
If you follow all these tips, you should be able to make your car a handling dream, and wipe the floor at the next SCCA Autocross event, the local road course or out on the curvy backroads.
-James
____________________ Project FocusFast
'06 ZX3- Intake, exhaust, mount
'01 ZX3- Salvaged, SOLD
'01 ZX3- Repo'd several years ago
'80 RX7 SA- Where the f*** did THAT come from?
