Brake lock up

I had a conversation with someone today and couldn't agree on something.

If you were driving a car at high speed in a straight line (say 250kph) and you could turn off the ABS, would you immediately get lock up if you stood on the brakes as hard as you can?

 

You wouldn't get it straight away, but you would as the car slowed to a much, much slower speed.

 

Why wouldn't you get it at high speed? F1 cars do.

 

I don't think a "normal" car would behave in that way.

Next time you are in an F1 car, give me a call. I'd like to see how you would handle it.

 

Can you turn the ABS off in the 355 ?

I'll go give it a try

 

You can in yours.....and I've done it and I got lock up at 220kph, completely screwing up my front tyres......but maybe that was abnormal.

 

Good thing you sold that car.

 

I think "thing" is the word you were shooting for.

 

Ha Ha

STFU and shoot off yourself.

 

Yes.

And if someone says no, I'd like to know why not.

Let me put it this way: If I stand on the brakes of the aircraft at high speed, it will lock up ridiculously quickly and easily. I know the wing is producing lots of lift therefore there's not much downforce on the wheels, but I can't see why it wouldn't lock up even if we chopped the wings off.

 

are you sure about the lift bit? for some reason I thought that under heavy braking while pulling back on the stick you'd actually put a fair bit of weight on the wheels. I actually have no idea why I thought that though.

 

On landing in most light aircraft if you pull back on the stick during the landing roll - as long as you are below stall speed - you will increase the "weight" on the main gear and therefore increase braking performance because you have increased the load on the wheels/tyres - Thus the braking performance is better.
However, if you are above stall speed and you pull back on the stick, the aircraft won't brake better, it will launch back into the air!

Bringing it back to cars, there is no reason that I can see why a non ABS car would not lock up at any speed if you stood on the brakes. Speed is pretty much irrelevant. If anything it may lock up easier at high speed, unless it was a car with aero which significantly increased downforce at high speed.

 

as much as I hate to agree with you.........

 

Shamefully predictably...

"You should do it more often because then you'll always be right."

What I really want to know is what the person with the contrary view was thinking

 

Yes.


**** Google, ask Horse etc......

 

I would have thought "it depends" on the road surface, tires and brake performance.

M

 

I think it "depends" on the co-efficient of friction between the tyre and the road

 

Why?

Most cars produce lift at high speeds, thereby reducing the amount of mechanical grip as speed increases (well, actually, almost anything produces lift as speed increases). This is independent of the variables you mention.
The only reason sports cars handle better and get "stickier" at higher speeds is because of artificial aero pushing them into the road.

There is no reason I can see which would stop a car locking up if you stood on the brakes at high speed without ABS active.

 

Ok..let's assume, for this example, that the co-efficient at friction is such that at 50kph, slamming your foot on the brake with ABS off would get immediate lock up. Would that still happen at 250kph?

 

I can say yes you can definitely as I had a jammed throttle at Phillip Island in a race car a few years ago going over the start finish line.
Once I hit the brakes both front wheel locked up instantly as I was trying to kill the engine. (I did have an enormous amount of life preserving force on the brake pedal as well lol).
Once the smoke had cleared, and the heart rate had settled a bit in the pits about an hour later, I checked the data logger and when I cut the engine I was doing exactly 250kmphr.

 

Finally a definitive answer! Thank you.

 

Absolutely

If you can't do it you need your brakes serviced

 

By definition of ABS, the brakes should lock up. They're designed to do so, that is, the calipers, pads and rotors can develop more friction than the road and tires in the best/worst conditions. Difference with the ABS is that the "locking" is intermittent.

 

To prove the hypothesis I don't believe you have to 'turn off the ABS'.

Driving at 250kph in a car with everything (ABS included) operating optimally standing on the brakes would do one of two things.

1. Slow the car, or
2. Slow the car with the ABS kicking you in the foot. Which means that WITHOUT ABS the best set of skiddies EVER.

I have experienced this at far slower speeds in different 4WD situations ... don't think the Range Rover will get up to 250kph

 

fixed.