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-   -   eliminating understeer (http://forums.pelicanparts.com/porsche-911-technical-forum/1013086-eliminating-understeer.html)

Driven97 11-15-2018 06:07 AM

It's been alluded to, but a car's handling cannot just be boiled down to understeer or oversteer. The hard part is being able to recognize when it's doing either, and if it's driver adjustable.

The simplest is steady state. Constant speed, constant radius, like on a skidpad. Tires, tire pressures, alignment, spring rates, and swaybars all affect this. And even here, in tightly controlled conditions, a car may act a lot different on a 100' skidpad vs a 300' one.

Then you can throw in dynamic stuff. Mid corner behavior is roughly equivalent to skidpad stuff, but in corner entry and corner exit weight is transferring around on the car, which brings shock damping into play as well on top of all the stuff listed above.

How much say that spring / bar / tire / shock / alignment has on vehicle balance is always in flux depending on the instant conditions the car is in. You could balance a car perfectly for a 100' asphalt skidpad on an 80° day by adjusting rear toe only, but that could (and would likely) make the car an absolute nightmare on power-on corner exits and at higher speeds.

Ideal goal is a car that a driver can make small adjustments and nibble on either side of perfect balance in all situations, but there's so many variables and tradeoffs that that's never fully possible. An F1 car, the pinnacle of motoring, would suck as an autocross car. It'd be super understeery and power delivery would be all wrong since it's so, so optimized for GP circuits.

Perfect example, as to the above question, changing torsion bars on one end and changing a swaybar on the other isn't a zero sum trade. Torsions act in fore and aft as well as lateral, where swaybars act only in lateral. So you'll change the character of the dynamics. Sometimes that's desired, sometimes not.

emcon5 11-15-2018 07:03 AM

Slow in, fast out.

kent olsen 11-15-2018 09:19 AM

I've had my 72 911 for 20 years. I've found the right tires, pressures, suspension, alignment, corner balance, and technique. To me the handling is near neutral. Then I bought a classic Mini Cooper and I thought you just point it and shoot. Talk about understeer!! Now I have to learn to drive that one differently.

adias 11-15-2018 10:05 AM

Quote:

Originally Posted by kent olsen (Post 10252787)
I've had my 72 911 for 20 years. I've found the right tires, pressures, suspension, alignment, corner balance, and technique. To me the handling is near neutral. Then I bought a classic Mini Cooper and I thought you just point it and shoot. Talk about understeer!! Now I have to learn to drive that one differently.

Precisely! You have two fantastic polar opposite driving platforms. Well done!

stlrj 11-15-2018 01:38 PM

Quote:

Originally Posted by emcon5 (Post 10252584)
Slow in, fast out.

But when you finally figure how to dial out the understeer, it becomes a lot more fun when you can take it fast in and fast out!

That's what happens when stock ride height and alignment to factory specs are adhered to.


Cheers,

Joe


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