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Discussion Starter #1
OK guys, here's a question I have for you. Does anyone know what the stock Mazda6 spring rates are?

The reason I ask is that I'm trying to reduce the understeer in my Fusion, and get better handling balance. As of now it rides on Eibach coils which are 20% firmer than stock, and a Racing Beat rear swaybar. The understeer tendency is reduced, but it is still VERY biased towards understeer. After reading posts here about seeing some oversteer with installation of the Racing Beat rear swaybar, I'm puzzled as to why the Fusion didn't respond as well to it. In every situation I've put the car into since adding the swaybar, the front just pushes.

At this point, I'm starting to wonder about the spring rate difference between the cars. From the measurements I took of the stock springs, the Fusion rates seem to be 198lb/in front, and 126lb/in rear. Is it possible that the rear springs in the Fusion are just too soft to allow proper balance? These rates just seem to be much lower than anything I've seen posted for the Mazda6. Any thoughts?
 

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Wow, those spring rates are low. The Mazda6 rates are a little higher, but not much. Your Eibachs are probably firmer. Regardless, if you have the RB rear sway, it's doing much more work than your springs and you should have sufficient roll stiffness back there.

I'd try installing the RB front bar too. Your front springs are still too soft and allowing too much body roll. When your body rolls, your front tires go off-camber and grip is reduced. I bet you're lifting a rear wheel way into the air (the rear sway is doing its job) but without more roll stiffness up front, you're still going to get that body roll.

Another possibility is that due to your lowering springs, you're running out of suspension travel up front. Your outer-front tire, the one doing most of the work, could be getting overloaded as it hits the hardest progresion of the bump stop and your spring rates go to infinity. I'm not sure what the Fusion bump stops look like though, but on the '6, they're fairly short up front and probably shouldn't be trimmed. (On the '6, I recommend simply not lowering the car much. You might instead consider Racing Beat or Mazdaspeed hatch springs.) Again, a front sway will help a little here.

Curiously, though, my Mazda6 (4cyl, not heavy V6) was extremely light on its feet and oversteer-happy on a totally stock suspension and RB rear sway bar.

Bump your front tire pressures up to 36-40psi if you haven't already, and consider aggressive summer tires if they're appropriate for your conditions.
 

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Discussion Starter #3
Thanks for the info and the help. It's becoming obvious that Ford softened up the spring rates from the Mazda6 for the Fusion.

I plan on installing the RB front sway, but didn't want to make the understeer worse. When I swap the stock shocks for the Konis, I'll try the RB coils. Hopefully that will get me the results I am looking for.
 

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Fusion spring rates are about 5% softer than Mazda6 in the front and about 10% in the rear. But remember that the 2in extra wheelbase on the Fusion means that they have more weight up front. They are also heavier over all, so even though the spring is only 5% softer, the ride frequency is probably about 10% softer. V6 rates are about 10% stiffer in the front vs I4 for both the 6 and Fusion.

As far as the jounce bumpers, they are the same as the 6. But the Fusion sits about 10mm higher at curb ride height, so the engagement will occur 10mm later into the travel.

The numbers I have (if I've converted my units correctly), are 227lb/in front and 130 rear for a V6 Fusion.
 

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the way oversteer occurs with the rb bar, is at the limit of cornering, when you lift. if you charge up to a corner and jack the steering wheel into the corner, you'll suprise the front tires, and youll get understeer. if you properly load the car into the corner, it will feel pretty neutral, perhaps a little understeerish until you start going faster. then, if you lift the throttle while at the limit limit ( sliding limit, not good idea for the street here) then the rear should come around. with progressive springs, the inputs hafta be a bit more exaggerated for the car to do what you want.


i say its driving style.
 

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If you are trying to eliminate understeer, then you are on the right track....

I would ditch the Eibachs (should be an easy sale on here or the fusion boards) and pick up some "mazdaspeed hatch springs" or RB's.... just as stretch said....

Also, when you are complaining of understeer, explain the circumstances....
 
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