A friend of mine crashed a 2007 Porsche gt3 at a high rate of speed, My question is if the vehicle had Anti Lock Breaks then why would it create such long skid marks? The Porsche did have a sport button does anyone know if this button disables any vehicle equipment or what exactly it does?

 

Maybe Sideways? ABS has no effect.

-td

 

Can't be sideways Long and straight as an arrow

 

Agreed.. based on the width of the marks, he was sideways at point of impact.. ABS don't help that.

 

and it wouldn't flip sliding sideways for that long?

 

those marks are quite wide apart and straight, wonder the angle of entry and if even there was any time for correction or any inkling of attempt...

 

Comment found on another Forum:

"I am a police officer as well as a profession*al collision tech/inves*tigator, and I will add my two cents to clarify what the skid/scuff marks show.

1) The skids in the left lane are tests marks that the police department*s use to measure the drag, slope, and friction of the roadway called the coefficien*t of friction. So you can rule out that there was a second vehicle in the left lane.

2) Dunns' vehicle was completely sideways as it struck the guard rail. The center scuff mark of the three is the rear passenger tire. As the center scuff begins to align with the left scuff, his vehicle is rotating clockwise."

 

^^^ that makes perfect sense. looking at the skid marks you can visualize the angle of impact onto the guardrail ... I am assuming the front far right skid mark are his front tires as I assume he would have had the brakes tightly locked up (although technically on an ABS equipped car they aren't supposed to lock up fully) ...

 

1. Marks seem to close together to be completey sideways. He was getting off at this ramp, the marks in the pic we only see half of the length they go back almost just as long. We are looking at half the length of the marks. He's driving at XXX mph at XXX mph + darkness of the night your perception of when this exit arrives is happening 3x as fast as normal driving. I know he pushed the speed to the end. I think he slammed the breaks locked the wheels slide straight into the guard rail hoping the Porsche would stop, but if that we're it wouldn't ABS not cause tire marks.

2.Lets say the car did not go straight, even if on an angle, how do we get the perfectly straight marks, no flip, and no spin? and again these marks continue perfectly straight further back a few 100 feet

 

I see what you mean sunir. I posted that last comment before I saw yours. I'm just having a hard time visualizing this since I know the road and he knew the road just as well he traveled this ramp 1000's of times. Why the spin sideways just simply trying to slow down, an animal, blowout? That Porsche could take this off ramp at 100+ mph. and thank you for everyone's professionalism on this

 

^^^ great questions.... this is text book of what they teach you in race schools and performance driving and what we try to teach students...this is a perfect example of intentional and deliberate abrupt weight transfer casuing what is known as power-on oversteer...or in this case accellerated power-on oversteer which is called snap oversteer...

Ryan sees the turn, he knows it's there assuming he's driven it 1000 times...he's drunk and he's like "oh $hit gotta turn" he misguages his braking poing, things move fast in a car at 130mph although prior to braking it's more like 145ish, his brain is reacting slower due to the alcohol (BAC of .196) ...

as he goes to turn and slow the car down in panic he engages severe weight transfer to the front inducing snap oversteer...at the speed he's going he continues to skid sideways as the sides of the tires are now perpendicular to the force vector of the car (sure ABS is active, you don't need to lock up the brakes to make those skid marks, you just need to be sideways and going so fast that the car has no time to rotate fully and you are hard on the brakes causing the tires to esentially rub off on the pavement rendering your usable contact patch area useless)...although the whole thing lasted for a split second in real life...in Ryan's alcohol imparied mind it was the slowest seeming forever skid and he could see the guardrail coming at him out of his drivers side door window...last words may have been " OH F*CK!!! " as the car slid toward the railing.

had he slammed on the brakes in a straight line to get the car slowed even if he was heading toward the rail those brakes would have hauled that Porsche right down, drunk driver or not...and Ryan may have been able to steer the car, with the tires contact patch doing what they are supposed to with the help of ABS...once slowed down to a much slower speed even say 60 or 70 he could have taken the ramp safely...but to do this he would have had to know that the exit was coming up and he waould have to have the reaction and not the alcohol induced mind to gauge his braking distance and the depth perception (also lost while drunk) to pull it off.

 

Makes sense now, Thanks

 

very sad

 

I would like to clarify what was said above about oversteer. Oversteer comes in two flavors, power on and trailing throttle. One example of power on oversteer is when applying power exiting a turn in the wet (from apex to track out) one gets on the gas too heavily or perhaps hits a transition from a patch to no patch and the back end steps out. Or in the wet one tracks out onto wet painted curbing, gets wheelspin, back end snaps. Or in the dry in second gear one enters a tight corner and gives too much gas and the rear steps out.

An example of trailing throttle oversteer would be entering a curve too hot, early apexing, realizing the car could run out of track on exit, lifting, and having the back end come around. Another is entering a turn too hot in the wet, getting understeer, adding rather than subtracting steering, and lifting, and the back end comes around. Or driving in a carousel, trying to breathe off the gas to eliminate understeer, overdoing it and lifting, and the back end comes around.

Ill executed trailbreaking could also cause the back end to come around. I would call this TTO because braking is an extreme form of reduced throttle.

I would assume that attempting to take an exit ramp would involve turning and lifting or turning and braking, so any oversteer would be TTO. Perhaps if driving at a high rate of speed one realized late that he wanted to take an exit, turned hard, got understeer, added steering, and lifted he could oversteer into a spin that would result in hitting a guardrail. Both feet in could lead to parallel skid marks straight down the road. With no ABS they would stay straight until stopping or impact. With ABS, as the car slowed the path would be an arc and the driver would eventually regain steering. So if you go both feet in on the track with ABS, don't quit driving, look where you want to go and eventually steer.

 

^^^^ that's correct the two types of oversteers power-on and trailing throttle both induce dynamic weight transfer to the front of the car...trailing the throttle can be used in many instances and often is on the race track to get the car to rotate at certain places and corners, the example illustrated as trail braking uses gradual shifting in the car's balance through deceleration while turning... a number of these factors could have been issues in the Dunn incident.