Snap oversteer
01-19-2010, 10:44 AM
#61
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Thank-you.
[QUOTE]Forward weight transfer under lift is going to be exactly the same under a given rate of deceleration, regardless of what spring and damping rates are.
[QUOTE]Forward weight transfer under lift is going to be exactly the same under a given rate of deceleration, regardless of what spring and damping rates are.
01-19-2010, 10:45 AM
#62
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Originally Posted by mikey stone,Jan 18 2010, 04:08 PM
Theoretically, when a car is cornering at the limit an abrupt lift will upset the balance and often cause the back end to get loose. The steering inputs can be buttery smooth, but that wont counteract physics of weight moving fore and aft at the limit of adhesion. If this were a corvette forum we could say the same thing about applying too much gas (the rear end will brake loose even while the steering inputs are smooth). But, it's a honda forum, so power oversteer is not part of the discussion (when traveling at the speeds you were going).
It's difficult to tell what is going on with the throttle in your first vid, but it doesnt look like you "threw" the car into the corner, rather the car was very close to/on the limit as you turned in (maybe a bit early?) and then you backed off the gas (to compensate for an early entry?), causing the rear tires to lose their grip. The save would have been to mash the gas and crack the wheel right (and then back left), but hey, that doesnt seem wise when you're going 100mph and staring at the boonies. I too have filled with my car with freshly cut grass and it smells awesome...
It's difficult to tell what is going on with the throttle in your first vid, but it doesnt look like you "threw" the car into the corner, rather the car was very close to/on the limit as you turned in (maybe a bit early?) and then you backed off the gas (to compensate for an early entry?), causing the rear tires to lose their grip. The save would have been to mash the gas and crack the wheel right (and then back left), but hey, that doesnt seem wise when you're going 100mph and staring at the boonies. I too have filled with my car with freshly cut grass and it smells awesome...
Coming from driving front wheel drive cars all my life I think I just have to learn that I might have to counter steer at an entry to be able to get on the gas and settle the car before turn in. Once that initial part is over then the car is extremely easy to manipulate.
no abrupt throttle but possibly abrupt initial braking which I'm working on
01-19-2010, 10:58 AM
#64
Originally Posted by CKit,Jan 19 2010, 11:43 AM
We're not talking about the forward momentum, but the change of weight over the front tires.
In that case, spring stiffness and rebound damping is absolutely related.
The center of gravity has an effect, but with soft springs and wimpy rebound damping that center of gravity actually goes UP under braking.
In any case, the center of gravity has a primary effect on how much weight transfer you get under deceleration. Again, fully developed weight transfer (the amount of load added to the fronts and taken off the rears) is simply going to be the car's weight times change in g's times c.g. height divided by wheelbase. C.g. height is FUNDAMENTAL to how much weight transfer you get. If you could move the c.g. underground, you'd unload the fronts and load the rears under deceleration.
01-19-2010, 11:10 AM
#65
Originally Posted by ZDan,Jan 19 2010, 11:58 AM
Not following you here. If you LIFT, causing deceleration, and you have a lot of rebound damping, then the front is going to compress and the rear will try to extened, but more rebound damping would reduce the rise at the rear. C.g. shouldn't go UP, should go DOWN. But not by a huge amount.
01-19-2010, 11:29 AM
#66
Holy CRAP, it sure does! Zat real? Gotta be a bump or undulation involved, I hope!
01-19-2010, 11:36 AM
#67
Anyway, keeping the tires in contact with the tarmac (which even a 65/35 fwd car should do under even the heaviest braking!), under decel, with more rebound damping and unchanged compression damping (normal state of affairs), the front should dive more than the rear goes up, hence c.g. should go up a tiny bit (a secondary effect as far as weight transfer goes).
01-19-2010, 12:16 PM
#68
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Originally Posted by macr88,Jan 15 2010, 10:36 AM
Here's the right video
.
01-20-2010, 01:53 PM
#69
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can any of you suggest a basic book that talks about suspension and chasis setups as it relates to tracking? I think it may help as a precursor to some of the points in this thread. I just found this: http://www.racelinecentral.com/Racin...e.html#CHASSIS ADJUSTMENTS
01-20-2010, 02:29 PM
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Originally Posted by mikey stone,Jan 18 2010, 11:06 AM
If you want to see something interesting do a youtube search for in-car video of s2000s spinning out. Pay close attention to how people deal with the steering wheel when the car starts to get loose (typically from a lift of the throttle once the car is on its way to the apex). You will see that a lot of spins are the result of drovers taking their hands off of 3 and 9 and letting the steering wheel slide through their hands, giving them zero ability to counter steer/corret. This "look ma, no hands" reaction is often a side effect of shuffle steering, and it's a particularly dangerous technique for an inexperienced drover in a tail-happy car like an s2000.