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<< I was on my way driving back to school and than I hit this turn on Middlefield heading towards Dennison. I have done this turn many times at the speed I was going (120 Km/H). I need no lecture about the speed I was going, as I have already recieved tons, and I knew what I did was wrong. My friend told me to slow down, but perhaps had I not listened to her, I would still have my car. The moment I applied the brakes, my rear started fish tailing towards the right. I counter steer to the right, I thought everything was ok. My car fish tails to the left this time, I counter steer and I 360 about 1 and a half times. My rear fish tailed into someone's backyard, destroying their fence. When I flew up the curb, my car almost rolled over. I still don't know what exactly happened or how I ended up where I did. If anyone is not familiar with the turn, it bends towards the oncoming traffic lane, but my car somehow ended on my side of the road, with the back of my car parked inside the fence. ... >>




Let's try to do an analysis here and make sense of it. I'm not familiar with the road but from what you wrote and what I've read let me share my opinion.

You said you were doing 120 and the car oversteer when you try to slow down by braking than spin.
What happens is a result of the changes in "front-to-back" & "side-to-side" acceleration.

The moment you take off your foot from the gas pedal, you starts a minor deceleration. This puts more weight on the front than the rear proportional to the deceleration. (no matter how much you lower your car). The rate of this weight transfer is directly linked to your rate of acceleration/deceleration (depends on your ref. direction).
By applying the brakes you are shifting more weight to the front.

Recall: Friction = coeff. of friction x normal force

Therefore, the harder you brake, the less traction you have with the rear tires. At this point, for whatever reason if there is a change in the side-to-side balance e.g. turning, the road is banked to the side (like those in nascar speedway)... etc. You are making the car more unbalanced than it already is.

In this case, when you are turning the front wheels, they are able to obey your order and turn. The rear, being light, does not have enough grip to hold the line and want to go straight, causing initial oversteer.

As the rear tire departs from the line where the tire is pointing to, it will generate more traction up to the maximum tire slip angle (about 7-8 degrees from what I read) when the traction decreases again. What it means is there will be a initial stage (consider yourself warned) where you have reasonable hope of controlling the car until a point when you rear become so uncontrollable that it feels like it is airborne. At this point, when you countersteer the front you will make the rear swing the the oppsite side, more than you wanted. If the condition is right, the angle in which the rear swing is the same as what you are turning in the front, your car starts spinning.

At the initial oversteer, being FWD, assuming you are not running out of space, the best you can do is smoothly let off the brake. Smoothly but quickly floor the throttle, at the same time, turn the front wheel to the direction the car is travelling and then smoothly but quickly steer the car back onto the line. You want to be smooth in order to not to upset the front but quick enough so that you are not going to run out of room and into the curb.
Put it simply, you have to use the engine torque to work against the momentum, PULL yourself out of trouble in time.

This is also how a pendulum turn works - you purposely spin the car 180 degrees and either push/pull yourself out of trouble, using engine torque to work against your momentum. Yes, this will waste fuel/brakes, hurt your tire big time, but when you are about to run over the cliff this is your only hope. People who master this skill take the trophy on WRC - not on streets.

Once you start spinning, the vehicle will travel in a straight line unless it runs into some sort of obstruction altering its path. Your best hope is have the ABS turned off and lockup all your tires. And let it stop in minimal time before running into a *tree*.

Drive smoothly and the car will reward you with advanced warning before you cannot control it anymore.

 
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Toronto, thanks for the detailed explanation. I could really relate to what you were saying, as what happened to my car is similar to what you described. So my question would be this Toronto: Would I have spun out of control if I was maintaining the same speed through out the turn as opposed to braking?

 
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My guess is ... if you were to turn the steering at 120, the car would undergo a massive understeer and head straight once it cannot hold the line, which is very similar to if you were to hit black ice in the winter at 30km/hr or more for a usual street corner. (assuming 3 season tire used).

When you turn, tires need to generate a cetripetal force, a force that points to the centre of the turn.
recall: F = m * v^2 / r
It is simply impossible to have a vehicle turning at too high of a speed. When it is possible to control, you can execute a pendulum turn to overcome the problem but it is only effective on low traction surface.

A tire can only do 100% of everything, if you used up part of the traction to provide the necessary centripetal force there is less than 100% left for braking. You can push it to the limit but no one can overcome physics.
To make a car turn and holding the line you have to run it under a certain limit speed. R-compound tires helps, lower centre of gravity helps, but there is always a limit. Know the limit and do not go over it.

Find an empty parking lot, space yourself comfortably, give it plenty of safety margin. Turn off ABS. Run up to 70km/hr or so and do an emergency brake (all in a straight line) without skidding any of the wheels. Do it several times (watch out for brake fade) so you get to feel how much brake effort is needed.
Repeat the above except trying to turn (holding a circular line) as well as stop as fast as you can. You should notice you cannot brake as stong as if you were running in a straight line.

Lets say you are driving in a closed track and there are 2 straights linked by a constant radius corner. Your car is able to brake as good as it can speed up. You would choose your apex in the middle of the corner (of course at the point cloest to the centre of the turning radius without going onto the grass/curb).

You start braking before you enter the corner in a straight line, smoothly but quickly goes into hard, maximum braking. You should have the right speed just before you turn the wheel and enter the corner. As you start to turn, you should use less & less braking (trail brake) until apex when you start accelerating. In general, the more steering you use, the less brake/gas you can use. The better you can balance these forces, the better your driving. This is no arcade.

Late apex (brake early, turn early, touching apex at a later point in the corner when accelerating) cornering will limit you to a lower entry speed but higher exit speed.
Early apex (brake late, turn late and tocuh apex at an early point in the corner, often still braking) will limit you to a lower exit speed but allow a higher entry speed.
How you choose depends whether there is a long straight after the turn where you will benifit from the higher exit speed. Or simply you need to get ahead of your opponent before the apex. Most of the time doing a late apex will allow you to "see" more of the turn

goto a Solo II school and readup more at Physics of the racing series

 
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How do you turn off ABS? Never knew you could do that.

 
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dont think u can take off abs
either it comes with it or it doesnt. its really good for the winter i think haha
ah well its all good
hope u learned from all of this.
i know i learned alot and i think im a more mature driver now![IMG]i/expressions/beer_yum.gif[/IMG]

 
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Toronto wrote an essay, j/k......... nice explanation

 
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damn i just read the first couple of lines and it was just too long but good essay as net said

 
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r u being my echo? hah

so how much did they give you unstoppable?

 
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All the money, including GST/PST, Freight, all that crap except for a couple of gov't taxes and the $500 deductible. Pretty safe deal. The insurance guy that we got is so nice. He's even letting me rent a car for a couple days more.

 
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unstoppable what insurance company? how much you paid a year for your car?

 
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<< How do you turn off ABS? Never knew you could do that. >>



either
1. with the car off, pull the ABS fuse (replace when done)
or
2. engage the hand brake one notch so that the brake is not engaged but the brake disabled warning light is on.

 
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hahahaha that explanations its kinda serious stuff
i think u can seriously damage the ride dude!!

 
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wtf that is wack

 
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sounds little bit dangerous

 
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yeah a little bit too dangerous [IMG]i/expressions/laugh2.gif[/IMG]