Normally I just drop the car and pick it up later but today I decided to hang around and wait for him to finish, since he could get me in and out fairly quick. After getting the car up on the lift he invited me into the shop to take a look around. My mechanic knows me well and knows I'm always interested to learn stuff about cars, especially the ones I drive regularly. So I stepped onto the shop floor and stooped down to take a look. The first thing he showed me was the rear suspension.
While I already knew the rear suspension was fully independent, I didn't know that it was also adjustable to some degree. My mechanic pointed a couple things out to me and told me they could easily fine-tune the setup to dial in a little more grip, at the expense of quicker tire wear. Intrigued, I told him to leave it be for now, and he moved onto the front end of the car.
Here he pointed out that the lower control arms were also a bit special. (The control arm is the part of the suspension that allows the wheel to travel up and down with the shock absorber, for those unaware). Most cars have the lower control arm mounted at one point to the wheel assembly. With my car, it's mounted at two points. While the downside is this makes the part more expensive to replace, the upshot is it adds a lot of stability to the front end, especially at high speed. This is what gives my car its rock-solid behavior on the freeway, and it's a design borrowed from German automakers, Audi specifically.
We then got to talking about the car's handling characteristics, as my mechanic owns a Mercury Milan (essentially the same car as the Fusion, with different badges and a slightly nicer interior). We both agreed that the car has a strong tendency to understeer when pushed hard into a corner. This is a common feature in most new cars. They're designed to do this, as understeer is a safe handling problem. You fix understeer by slowing down. He told me this problem could be easily fixed by the addition of a bigger rear sway bar.
So of course that got me thinking. A sway bar, perhaps a set of progressive-rate springs (progressive-rate springs get stiffer and stiffer the more they're compressed, providing a compliant ride as well as sharp cornering at the limit), a front strut tower bar (to stiffen up the front end and sharpen up the cornering), and a few other bits and bobs, and before I knew it my shopping cart at Summit Racing had about a thousand bucks worth of stuff in it. Boy it's a good thing I have some self control, otherwise I'd have been skipping work to make a parts run with Mastercard in tow.
If you ever get the chance, crawl under a Mazda 6 - the chassis should look eerily familiar... Ford ported the last gen Mazda 6 chassis with some improvements that the Mazda engineers hadn't implemented, one of those being the control arm setup you describe.
ReplyDeleteIn terms of dialing understeer out, another big thing that will help is a rear shock tower brace in addition to the meatier sway bar you've already talked about getting. The only caveat to this is that front wheel drive cars can be somewhat touchy as you dial their natural understeer out. The way the factory has it set up, power on into a corner will give you fairly severe understeer, and as you lift it degrades to mild understeer and then mild oversteer as you scrub speed. If you dial out the power-on understeer, what you might find is that you get far less transition time from understeer to throttle-lift snap oversteer in a corner at speed. Just something to watch for as you're modifying a front driver.