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Old 05-03-2005, 03:22 AM   #1
enzo
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understeer?

would someone explain to me what understeer is? i'm wondering because my friends got me all confused. and don't make fun of me because i don't know what it is! thanks.
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Old 05-03-2005, 04:41 AM   #2
dodgerforlife
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a) google it
b) your friends probably have no clue either.

"In real world terms, understeer is when the car won't turn any sharper, even if you turn the steering wheel more. At some point, the front end may start to grip less even when the steering is turned sharply and the result is the car continues in more of a straight line than a sharp turn."

<<quote not mine...i just finished that interest math problem...too lazy to think>>
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Old 05-03-2005, 09:25 AM   #3
abless
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A problem related to front wheel drive setups. With RWD, no matter how much throttle you input, the pressure on the steering wheel remains basically the same. FWD likes to straighten out when aggressivly throttled because the same wheels being driven are being turned.
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Old 05-03-2005, 02:47 PM   #4
ChrisV
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Quote:
Originally Posted by abless
A problem related to front wheel drive setups. With RWD, no matter how much throttle you input, the pressure on the steering wheel remains basically the same. FWD likes to straighten out when aggressivly throttled because the same wheels being driven are being turned.

Umm, no.

Understeer is when the front tires lose grip earlier than the rears, and the car wants to go straighter than the turn. This can happen just as easily with RWD cars, and is extremely prevalent in softly suspended front engine cars. Big engine musclecars were usually horribly understeering pigs when it came to cornering. So are most luxury sedans.

It's all about how much weight is transferred to the outside front tire in a corner, and how quickly the steering input is given.

Here's a Porsche oversteering. The car is going around a right hand bend, but the rear is turning more than the front, so the driver has to steer to the left to keep the car going around the corner correctly:


http://www.dleong.org/2001/ggr8/jtavernetti/photo02.jpg

Here is a Porsche understeering. Notice how the front tires are turned more than the car is turning (and there is a dust trail showing thet the front tire is being dragged in the direction the car is pointing, not where the tire is pointing):


http://www.dleong.org/2001/ggr8/jtavernetti/photo05.jpg


This older RWD car is understeering heavily. The front tires are turned, but the weight transfer (as indicated by the body lean) is all the way on the outside front tire, which is not gripping well, and the car is going much straighter than the steering input:



The key to eliminating understeer is to keep the outside front tire from being overloaded. On a front heavy car, that usually means managing weight transfer away from the outside front tire using spring rates and swaybar size. the simplest solution is to increase the rear swaybar size (or install one if there isn't one). This transfers more weight to the inside rear tire, balancing the car out.
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Old 05-03-2005, 11:09 PM   #5
chloroform
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a little toe-out in the rear and or toe-in in the front can also be used to reduce understeer? what about camber? is this to correct the understeer problem coming out of a corner or going into? how does this matter?
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Old 05-04-2005, 12:04 AM   #6
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Quote:
Originally Posted by chloroform
a little toe-out in the rear and or toe-in in the front can also be used to reduce understeer? what about camber? is this to correct the understeer problem coming out of a corner or going into? how does this matter?


Toe out at the rear can do it, though you will tend to wear your tires worse, and make it slightly unstable. Toe in at the front wil merely make teh outside front tire turn more for eth same steering input, which can make teh problem worse, as well as wear your tires more.

Increasing front camber slightly will help better, as the tires will tend to ride flatter in the corner as the car leans over, giving a wider contact patch, resisting sliding out more. But again, don't overdo it, or you can wear your tires really badly on the inside edge.

The best way is still controlling weight transfer with spring and swaybar rates. The cheapest is by adjusting air pressures (increasing front presssure and reducing rear pressure can reduce understeer, by giving the front tires more grip).
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