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oversteer

Old 06-16-2006, 10:45 PM
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oversteer

i noticed almost everyone has their setups with stiffer shock setting and spring rates in the front. wouldnt it handle better and induce a little oversteer with stiffer rear settings, spring rates?
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Old 06-16-2006, 10:59 PM
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IMO, depends on your application, tire/wheel size, and driving style

Autocross guys like for the car to rotate, since the course is setup very tight with sharp turns. However they are still daily drivers and it wouldn't be a good idea to run a 9kg F/ 12kg R setup. Its easier to run a bit less tire in the rear (on track wheel/tires) instead of changing springs back and forth

I like the car to understeer a little, since I only do road courses. Plus it makes the car easier to control at the limit (just let off the gas and apply the steering accordingly). Remember that most people buy their suspension as a package setup and learn to work with it. You won't see an aggressive rear spring rate on a package setup for a generic application.

Coilover springs on the other hand get quite expensive also ($120 a pair from Eibach)
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Old 06-17-2006, 12:38 PM
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stiffer rates in the rear will indeed induce more oversteer, however, most producers of coilover solutions for our cars include significantly stiffer spring rates for the front than the rear, for the most part this is not entirely done for the safety of generic FWD (FF) "push" understeer characteristics at the limit, it is also done in consideration of a inherently front heavy weight bias which plagues our cars, making stiffer spring rates to support and fight body roll in the front necessary than in the rear. Also consider that rollover on our front macpherson strut suspension geometry often results in neg camber loss under compression, so you would want to resist roll as much as possible whereas in the rear, given our beam suspension which already acts to stiffen the rear (as it is almost like a giant RSB) in a sense, the wheels are connected together on each side and maintain their perpendicular nature under load/compression and keep their -1 deg neg camber as provided from the factory, once again, higher spring rates are not entirely necessary.

Now let's look at the other FF cars out there which are highly competitive in both autoX and road coarse arrangements, such as the EG6's, EK9's and various other civics and such...they run much higher spring rates in the rear than the front....even though they are still front heavy...why? because at a certain point in every drivers career and driving abilities, FF cars will never rotate enough for the drivers taste and will seemingly always understeer, overheating the front tires during road coarse sessions oftentimes, reducing traction and braking ability as they get "greasy". The ability to have the car to rotate without having to use "trail braking" excessively--that is to say using just throttle off techniques, will result in a massive amount of turn in without the need to scrub off significant speed and more fade possibility by utilizing heavy amounts of trail braking while entering the corner (which as we all know, is the traditional technique to get a FF car to turn-in and still be decently competitive rather than understeering and scrubbing off too much speed)...all of this of course really pays off when you realize that the less slip angle you have from the front tires/understeer, the sooner you can apply throttle to power out of the corner on to the straight which follows until the next turn...(eg. see theory on tire traction circles).

of course, in the end, it is more beneficial for the average, novice, and oftentimes even the intermediate driver to have a naturally understeering maxima especially if it is your daily driver, which is why I am keeping my stiffer front than rear ratio for the time being. I suggest tinkering with easier to adjust things to stiffen up the rear or soften the front for the time being such as strut settings and adj. rear sway bars...that way you can judge whether you enjoy or take advantage from more oversteer in your driving and can easily undo it, whereas with changing springs, it can get costly and labor intensive to keep switching...
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Old 06-17-2006, 01:25 PM
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thanks, exactly what i was looking for.
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Old 06-17-2006, 06:49 PM
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You also gotta take into account that raw spring rates are very different than wheel rates (usable spring rates from the wheel's point of view)

Motion ratios, spring angle, angle correction factor, and then the anti-roll bar rates all factor into account. Even without the FSB/RSB figured in my rates of 700f/450r calculate to more rear rate than front. Heck 550f/350r works out to nearly equal (rough calcs)
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Old 06-17-2006, 07:40 PM
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My overall setup is for *very slight* understeer daily driving, which is safer in the event of emergency maneuvering, but for track, I set it up to oversteer by softening the front struts and running very high tire pressures in the back (among other things)....small things like that can make a difference..
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Old 06-17-2006, 08:28 PM
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right, easiest and cheapest way to dial in more oversteer....is definitely add more rear psi in the tires bar none!
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Old 06-19-2006, 02:57 AM
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There's another reason for the usual relationship between front and rear spring rates.

Primarily, it's for buyers who don't drive in cornering competition of any sort, and it's to maintain the OE "flat ride" characteristics. It's a ride comfort consideration, where you DON'T want the front end rising while the rear end is dropping after going over a bump or "heave" in the road. In the extremely poor case, think "constant front to back head snap, for which my usual example is an old pickup with HD rear springs, dead shocks and nothing in the bed.

As long as your shocks provide enough damping, it's not a huge issue. But even the aftermarket does not place lots of faith that all their potential customers would replace shocks/struts before making complaints about a poor ride.

I've got some comparative plots that show this graphically, from a large-ish but not particularly complex spreadsheet.

Norm
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