While Braking - Car Sways
02-28-2009, 06:41 PM
#12
AudiWorld Super User
Sway almost always shock absorbers. unmatched tires maybe pulling
but swaying is an undamped dynamic issue.
Recognize that brake fluid pressure is a non starter...by definition the pressure is the same except for rear brake proportioning if presetn.
Recognize that brake fluid pressure is a non starter...by definition the pressure is the same except for rear brake proportioning if presetn.
02-28-2009, 07:42 PM
#14
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Is your second sentence a question or a statement?
When did I say anything about width? I was talking about the tire as a whole. He's got one tire, the 255/40, with a diameter almost a full inch less than the other three. Not a great long term situation.
Koz.
Koz.
02-28-2009, 08:15 PM
#15
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Well, he's got a 225 on one front axle, and a 255 on the other...
I can see where a pull toward the 255 side under braking, and the ensuing steering corrections, would cause a sway. Certainly the fact that shocks are probably 9 years old allows the sway to occur, but they are not the cause per se.
Koz.
Koz.
03-01-2009, 03:16 AM
#16
AudiWorld Super User
The mismatched tires would cause the impulse/pull...the bad shocks cause the sway.
03-01-2009, 07:41 AM
#18
AudiWorld Super User
go to basic spring/mass/damper vibrational analysis.
If the shocks were adequate the braking action would impart an unbalanced impulse rather than a straight fore/aft or even a pitching motion. Even with bad shocks, such a balanced impulse would at worse induce a pitch (rather than a yaw, which is the beginning of a sway) that would or would not damp out adequately. U see it all the time, cars with worn shocks pitching up and down as they go down the road.
An underdamped system will overshoot and undershoot at least once; critcal damping is one overshoot, no undershoot; overdamped is no overshoot.
With an unbalanced impulse, you get a yaw impulse that, with worn shocks (generally the underdamped situation), cannot be adequately damped and the result is a sway or, to use the continuous form, a swaying, a repeated yaw right/left or vice versa motion.
Perhaps the vernacular is swaying you....a sway may be one or an incomplete cycle, a swaying is more than one cycle.
An underdamped system will overshoot and undershoot at least once; critcal damping is one overshoot, no undershoot; overdamped is no overshoot.
With an unbalanced impulse, you get a yaw impulse that, with worn shocks (generally the underdamped situation), cannot be adequately damped and the result is a sway or, to use the continuous form, a swaying, a repeated yaw right/left or vice versa motion.
Perhaps the vernacular is swaying you....a sway may be one or an incomplete cycle, a swaying is more than one cycle.
03-01-2009, 08:21 AM
#19
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Normal braking + bad shocks = dive. Normal braking + bad shocks + unequal braking forces upfront =
sway. Therefore, the newly introduced variable is the "cause". I think we're just playing semantics here. The "pitching" and "swaying" is not "caused" by the bad shocks but rather by forces acting on the car's intended path. Bad shocks just allow these forces to unbalance the car.
Koz.
Koz.
03-01-2009, 08:45 AM
#20
AudiWorld Super User
You didn't notice the (!)? "When did I say anything about width?" In your previous post, 225 vs. 255
You weren't talking about the tire as a whole, only about tread width in comparing the first numbers. The second numbers, the sidewall height, were not disclosed, so you're just guessing.