Brakes vs. Engine


#1

If you stand on the brakes and try to accelerate will the brakes have enough stopping friction to keep the car from moving and stall the engine? If you are going full throttle and keep the pedal to the floor as you apply the brakes which will win out the brakes or the engine?


#2

Are you too young to drive?


#3

It depends on the car (some brakes are better than others, and some engines are better than others), how fast it is going when this starts, and if you stand really hard on the brakes and don’t let up or if you pump them or apply them at less than full force. (The brakes will probably lose if you pump them or don’t start with them at full force and keep it that way.)


#4

And in light of the recent “unintended acceleration” concerns, many newer cars are being programmed to give braking full priority over any open throttle position.


#5

Unless the engine stalls something will give, and it’ll probably be in the tranny or the drivetrain, depending on the vehicle. Anybody want to buy a hardly used torque converter?

Try it in a Toyota Tacoma 4-banger and the engine will probably stall.

Try it in a Camaro and you’ll probably burn something up. Hint: the TC converts the difference between the engine and the tranny input shaft ultimately into heat.

Try it in a Bugatti Veyron SuperSport (1200 HP, carbon-ceramic discs…VERY oversized) and the parts between the engine and the tranny will probably take your legs off when the explosion occurs.


#6

Time to take out those dusty high school physics notes

Consider the newest 2010 Porsche 911 Turbo, which goes from 0 to 60 mph in 3 seconds
60mph ~ 100km/h = 27.7 m/s

Acceleration is equal to change in speed (27.7m/s) divided by change in time (3 seconds) = 9.27 m/s/s. That is a little short of 1 g. Most tires are capable of handling 1 g before they start to skid. If you slam on the brakes in said Porsche, you’re likely to trigger ABS, which means you’re pushing the tires beyond 1 g.

If you aren’t lost in those physics and math, you’d see that brake wins even in something as powerful as that. If we are talking about a mediocre sports car that does 0-60 in 6 seconds, that’s roughly 1/2g from the engine. For a subcompact, we are looking at 1/3g.


#7

A 1958 Chevrolet with a 348 engine will torque up, break the bell housing and blow off the torque converter which may come through the floor, through the dash, and into the windshield before coming to a stop. It was spinning the wheels and plowing forward when it blew. The drivers father was very unhappy.


#8

Car and Driver magazine recently did a real-world test of this with several cars. On all of the cars tested the brakes were capable of stopping the vehicle, even at WOT (wide open throttle).

The Rousch Mustang, with 400+ HP, took the longest to stop but the brakes still brought it to a halt.

I suppose there are exotics or racing vehicles out there in which the engine might win, but for any vehicle you and I are likely to encounter in our lives the brakes will win.

You will have to press REALLY hard on the brake pedal, however. People are afraid to do this, which is why all these runaway cars are reported. Camrys and Corollas are not powerful enough to beat the brakes.


#9

You shouldn’t have shown your work. You got the right answer, but via the wrong methods. The g forces the car pulls have nothing to do with it. The car isn’t moving in this case, and so it’s a 0g situation all around. Your examples also fail to take into consideration static friction. Brakes are a good deal “more powerful” when the car is already stopped than they are when trying to slow the car down.

That’s why the unintended acceleration issues Toyota had are a matter of such concern. The brakes can easily overcome the engine’s power when the car isn’t moving. But when it’s doing 60mph, and you hit the brakes while still under full throttle, you’ll end up cooking your brakes before you can stop, even assuming the brakes are effective at all at wide open throttle at the peak of the powerband. Once the brakes lose effectiveness, you’re pretty much toast unless you can get the car shut off.


#10

I agree. Either the engine will stall or something will break. Since the torque converter ultimately dissipates the energy as heat, my guess is it would be an expensive experiment. And probably a hot one. My guess is that you’d smell something burning, and the engine would suddenly rev free, unencumbered by load from the drivetrain. And the letter “D” would no longer connect the engine and tranny. “D” would change its meaning from “drive” to “dead”.


#11

So…were you grounded?


#12

Depends on the vehicle. A 1969 Buick Skylark with a 350 V8 and 4 wheel manual drum brakes, the engine will win. A 2000 Blazer with 4 wheel power disc brakes, the brakes will control the speed until the trans can be shifted to neutral and the engine shut down.

Ed B.


#13

Well the op is talking about holding a car stationary with brakes. The brakes has the ability to supply more force than a full throttled engine. The NET force on the car is zero but the forces from engine and brakes are far from zero. At any speed, if the engine applies a force on the car, it accelerates. If the brakes applies a force, the car decelerates. When those 2 opposing forces exert themselves on the car, it accelerates in the direction of the net force. And as I pointed out, brakes, unlike the engine, generate more g than the tires can handle.

Also, force is not power. Power is the rate at which work is done–you can’t measure the power of brakes when the car is stationary. Since rate is involved, it applies to incidence where a car is stopping with a stuck throttle. As another poster mentioned already, Car And Driver did this experiment in which they stopped a full throttled Camry with brakes. The brakes was able to remove more energy than the engine was supplying in the same period of time. Therefore, brakes are more powerful than engine.


#14

Brakes do not generate g-forces when the car is stopped. An engine that’s overpowered by the brakes at rest does not generate g-forces either. g-forces have nothing to do with it.

It’s a question of resistance-from-friction. If the brakes can supply enough friction to keep the engine from moving the car, then the car wont’ move. If they can’t, then it will.

To illustrate why the g-force approach is prone to error, take a look at the Komatsu super dump trucks. I’ll just about guarantee that the 2,000+hp engine can overpower the wet disc brakes on those trucks, (not that anyone’s actually tried it, because if the engine can’t the destruction of the truck would be spectacular just before the driver was killed) yet the g-forces experienced on acceleration will be almost negligible, and probably less than those experienced when braking.

And I know about the difference between force and power. That’s why I put “more powerful” in quotation marks. I know that’s not an accurate way of describing it, but the accurate way of describing it is more confusing to those who are not up on their physics.


#15

Sounds like an inventive way to shorten the life of someones else car…I hope it’s paid for or you have enough toy money to repair it.


#16

There’s gravity, electromagnetic, strong and weak nuclear force, as accepted by physicist for now. I’ve never heard of g-force. Force is a force. Whether or not it accelerates an object depends on the net force applied to the object.

I used the acceleration numbers pulled from a magazine to estimate the average force from a Porsche’s engine because I’m not rich enough to put a 150k Porsche 911 on a dyno. If you have a better idea, then lets hear it.

Also, power = force x velocity. Velocity goes up and force goes down. I’m not saying there exist a brake system that can overcome 2000 hp. If geared properly, brakes do not need to exert a lot of force to win over 2000 hp. What they need is a cooling system that continuously remove heat energy.


#17

Well, from experience I can tell you if you do it (power brake) enough times in a '68 LeSabre you will probably blow the gears out through the pumpkin in the rear end. No, Dad was NOT happy! Ouch! :frowning:


#18

Cool. None of us even thought of the rear end. In modern cars it’d probebly be the transaxle housing and then the firewall that they’d escape their misery through.


#19

I give chunky the nod here.

The car that’s 0 to 60 in 6 seconds travels approx. 265 feet in that time.

Most cars can stop 60 to 0 in 130 to 150 feet, so deceleration is stronger in that speed range.

However, the engine has more mechanical advantage (leverage) in lower gears.


#20

I was driving the Ford that he was trying to beat off the line.