major brake problem.. almost wrecked
05-26-2004, 04:48 PM
#1
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major brake problem.. almost wrecked well i was on my way home and came around a corner and the trafic was at a stop, i had plent of time but i hit the brakes, just semi-hard, and then the back end was next to me tried to correct it but to late, it swung the other way then back to the right and i started going backwards and almost did a 360.. i ended up spinning 3/4 of a turn... and i was just wondering how that could happen, once it started to spin, i let go of the brake , but i thought we have anti-lock brakes?? o well, i didnt hit anything but my tires are kinda trashed though... 
05-26-2004, 08:56 PM
#4
ABS can prevent lockup of a wheel. It can't protect you from weight transfer. If you are in a corner at "max grip" (nearly sliding) and stab the brakes, you shift weight to the front tires, this unloads the rear tires and that reduces their grip. Once grip is reduced (and you were using "all of it" already) you will lose traction in the rear and the car will spin. You shifted grip to the front tires and the rear grip was reduced to less grip than you were using at that time (less grip than cornering load means something is going to slide).
There is something called the "traction circle". It is a graph of a tires grip. Meaning how much grip a tire makes at each angle (accelerating, braking, turning, turning more, turning more than that, etc). A tire only has a certain amount of grip. You can use that grip to accelerate, brake, turn, or any combination of those (but at a reduced level). For example, if you floor the car and twist the steering wheel, you'll do a doughnut. Because you are using all of your grip for acceleration and there is none left for turning the car. Or, if you are in a hard turn and stab the gas, the rear will slide. You are using all of your grip for a corner and there is none left for acceleration. You did exactly that, but in reverse. You were cornering hard and tried to brake. The tires didn't have enough grip to turn and slow the car. Add the fact that slowing the car shifts weight forward which reduces grip and you are headed for trouble in a hurry. The result will be exactly what you had happen. I'm just glad to hear that you and the car are ok.
This is an excellent article (a little technical, but not hard to follow and the pictures explain alot).
http://www.miata.net/sport/Physics/07-Circle.html
2 more links I found.
http://www.dur.ac.uk/r.g.bower/PoM/pom/node23.html
http://www.dur.ac.uk/r.g.bower/PoM/p...ml#figtraccirc
There is something called the "traction circle". It is a graph of a tires grip. Meaning how much grip a tire makes at each angle (accelerating, braking, turning, turning more, turning more than that, etc). A tire only has a certain amount of grip. You can use that grip to accelerate, brake, turn, or any combination of those (but at a reduced level). For example, if you floor the car and twist the steering wheel, you'll do a doughnut. Because you are using all of your grip for acceleration and there is none left for turning the car. Or, if you are in a hard turn and stab the gas, the rear will slide. You are using all of your grip for a corner and there is none left for acceleration. You did exactly that, but in reverse. You were cornering hard and tried to brake. The tires didn't have enough grip to turn and slow the car. Add the fact that slowing the car shifts weight forward which reduces grip and you are headed for trouble in a hurry. The result will be exactly what you had happen. I'm just glad to hear that you and the car are ok.
This is an excellent article (a little technical, but not hard to follow and the pictures explain alot).
http://www.miata.net/sport/Physics/07-Circle.html
2 more links I found.
http://www.dur.ac.uk/r.g.bower/PoM/pom/node23.html
http://www.dur.ac.uk/r.g.bower/PoM/p...ml#figtraccirc