Looks like everyone has it correct. The brakes are about 3 or 4 times more powerful then the engine judging by zero to sixty and sixty to zero tests. And I have actually done the stomp-on-both-pedals test myself years ago with a Firebird. In that case the rear brakes slipped a bit but the fronts held steady.
My car’s throttle got stuck open while I was on the highway and I had a hard time slowing down - a terrifyingly hard time. Fortunately I managed to do it; if I hadn’t been so scared I would have used neutral sooner.
Fwiw, left-foot braking (under power) is a standard technique in racing. Not exactly responsive to OP, since this obviously does not involved just stomping on both pedals as hard as you can, but modulating relative input of power and braking to control a turn.
One common race situation that requires left-foot braking is when a racer is cornering under power. If the driver does not want to lift off the throttle, potentially causing trailing-throttle oversteer, left-foot braking can induce a mild oversteer situation, and help the car “tuck”, or turn-in better.
In rallying left-foot braking is very beneficial, especially to front-wheel drive vehicles.[3][4] It is closely related to the handbrake turn, but involves locking the rear wheels using the foot brake (retarding actually, to reduce traction, rarely fully locking – best considered a misapplication), which is set up to apply a significant pressure bias to the rear brakes. The vehicle is balanced using engine power by use of the gas pedal, operated by the right foot. The left foot is thus brought into play to operate the brake. It is not as necessary to use this technique with rear-wheel drive and four-wheel drive rally vehicles because they can be easily turned rapidly by using excess power to the wheels and the use of opposite lock steering, however the technique is still beneficial when the driver needs to decelerate and slide at the same time. In rear wheel drive, left foot braking can be used when the car is at opposite lock and about to spin. Using throttle and brake will lock the front tires but not the rears, thus giving the rears more traction and bringing the front end around.
It’s fundamental to rally driving, lesson 1 here:
To power brake an automatic transmission rear wheel drive car, you apply the brake and the gas, the front brakes will hold the car, let up on brake a little and the front will hold while the rear spins. You can sit in one spot and just roast the rear wheels in a cloud of smoke. Then let off the brake all the way while still spinning and lay down a bitchin set of black tire marks.
I could sit in one spot and burn the entire rear tires off my car until they blow out should I choose to do so. Your results may vary.
It should be mentioned here that, any time you’re leaving tire tracks, you’re at less than the maximum possible acceleration (whether positive or negative). Sliding friction is always less than static friction.
A little wheel slipping isn’t necessarily bad. We got some new snow during the last couple weeks and I found some opportunities to safely goof off. A new driver could benefit from the experience of driving at or just beyond the limits of control.
Perfectly level flight is the supreme challenge of the scale model pilot.
If it’s a conventional front wheel drive car with disc brakes at the front and drums at the back, that’s right - because in that configuration, the foot brakes primarily act on the front disc brakes, so the transmission is trying to drive the front wheels while the foot brake is locking them solid; the engine stalls. If the clutch is old and close to its wear limit, I suppose that might slip and then burn out.
If it’s a conventional rear wheel drive car with similar brake configuration, the front wheels lock and provide resistance to forward motion; the rear wheels spin in place and emit copious smoke (I believe this is called a ‘burnout’) - the rear of the vehicle may shimmy and move about.
So a couple of comments:
The question was posed while getting into a car before starting it, so I assume the context of the question was “from a dead stop”.
But, the recollection that people cannot stop cars with “stuck accelerators” by mashing the brake pedal is indeed one of the things in my head that assumed the engine can overpower the brakes.
Interesting to learn about “left foot braking” a car for rally racing, pretty advanced stuff though for a new driver, haha. I am familiar with the idea of using front/rear brakes at separate levels, even while still applying throttle, for a motorcycle, never thought a car could do the same because there is only one brake pedal, interesting to see that one can still “bias to the rear” with the right technique.
Teslas will put up some sort of error message, and cut power.
My understanding is it’s a failure to “mash” that’s the problem. If the throttle is open enough to be going 70 MPH, and the brakes are pressed hard and held there, the car should eventually come to a stop. At some point the engine will either stall (manual) or start dumping lots of heat into the torque converter (traditional automatic). I supposed things like DCTs and CVTs will do whatever they do.
If, however, the brakes are only pressed a little bit, maybe as much as someone would when trying to gently slowdown from 70, the car will lose some speed, but will not stop. During this time heat will continue to be dumped into the brakes, until they eventually fade, and are no longer able to stop the car regardless of how hard they are pressed.
Related: a friend’s brother had a buddy who liked to rev his dad (the minister)'s big V8 up in neutral and then drop it into gear. Much lurching, burning rubber, and hilarity. Until he did it one time too many and instead of fun, there was a loud noise and the car would barely move after that. He’d borked the torque converter.
Not quite what OP’s student was asking about, but in case you ever wondered.
I thought that too, but according to Consumer Reports
(YouTube link), when the acceleration happens when you’re already moving at a decent clip, the brakes may not be strong enough.
Interestingly, it seems to me that pre-antilock brakes, the brakes would’ve always won, if you were willing to skid. Because if you stomped on the brakes, they would lock up, and then you’d basically be back to the standing start scenario, where the engine can’t overcome brakes when the wheels aren’t turning, and you’d skid to a stop.
In addition, the idea that people just need to brake harder may need a reality check about what the practical limits of brake pedal force are. See .pdf link below.
I don’t have any proof, but I have a hunch that accelerating out of control from any cause in a manual transmission car is so exceedingly rare that in practical terms we can just call it never. If you drive a manual proficiently, hearing the engine rev up, especially when you’re not wanting it to, will pretty much instinctively get your left foot moving toward the clutch. The car would never really get going before the clutch would just stop the transfer of power from the engine to the drive wheels. (Whereas, as the guy in the video mentions, lots of automatic drivers have never put their cars in neutral.)
The speed bumps in the parking lot of my high school were yellow except for the black skid marks from kids doing that much too often.
I’ve told this story before, but it fits here sorta. The trigger words being “proficient” and “neutral”.
Back in college I hopped up a manual transmission car then sold it to some guy who fancied himself a hot car driver. For the era, it was a pretty hot car. Back then cars had ignition keys on the steering column.
A couple days later he’s cruising down a freeway, decides to floor it, and the throttle sticks wide open. Real quick he’s going real fast. He’s smart enough to stomp the clutch and the brakes and begins to slow down rapidly. Yaay!
He is not however smart enough, nor has presence of mind enough, to shut off the ignition. With WOT & no load, and a decade or two before electronic rev limiters were invented, the engine blows about 10 seconds later at WAG 150% of redline. Boo-oh!
All he had to do was turn the key one click from “on” to “off”. He came back to me blaming me for the problem and wanting a new engine. Nope. Sold as was-where was two days ago and your blown engine is all on you.
I asked him why he didn’t just turn the key to “off” before depressing the clutch and unloading the engine. He said “That would lock the steering column.” In further discussion it became apparent that he, a ~25yo car-crazy male, had never heard of, or noticed, the presence of an “off” position in the ignition switches between “lock” and “on”. Which existed in every car of every make that had a steering lock feature. And had for the then-almost 10 years such ignition switches were the norm.
Moral of the story:
People who don’t know anything about the tools they use are very much unable to deal with minor oddities, much less actual emergencies, involving those tools.
Once after I got an oil change, the ‘change oil’ message was still on. I called the place and they said “oh, we forgot to reset it”. They explained how I could do it, which involved pushing the gas pedal to the floor and holding for a few seconds. It occurred to me that if someone, not too bright, thought the vehicle needed to be running while resetting the message, that might not go well at all.
Considering the vast array of buttons and switches in a modern car that could be used to trigger a “cheat code”, designing the system so a floored gas pedal is one of them seems … unwise. Even if it is meant to be done with the engine off.
There’s a phrase the personal injury plaintiff’s bar likes to use: “foreseeable consequence.”
And if the driver absolutely floors the pedal, but it’s the wrong pedal, then the car definitely won’t stop. Usually, that’s the reason why the “accelerator is stuck” to begin with.
Interesting, but I have no intention of trying it. I hope if it ever happens to me I have the presence of mind to drop into neutral. Really, having to use the brakes to overcome a wide open throttle should only ever be necessary if for some reason the transmission is also broken in such a way it’s stuck in gear.
Yeah, it’s difficult to see how it would happen at speed in a manual. I have had it happen from a stop or very low speeds in a manual when my wet shoe slipped off the clutch pedal. That tends to be self limiting, in that the car may lurch, but then the engine will stall. Potentially regrettable in a parking lot.
I’m convinced that nearly every single incident of unintended acceleration from a stop is pedal misapplication. I think that is less likely at speed, but I’m sure it’s happened. A few times I’ve hit the brake thinking it was the clutch, and if you try to press the brake to the floor when shifting, failure to stop is not one of the resulting problems.
A failure mode not often addressed is computer software failure.
Nowadays in most cars the throttle pedal, the gear shifter, and the engine on/off button are all just inputs to computer(s). None of these controls are directly and simply attached to the thing they control. Given that design, it’s conceptually possible for every one of those inputs to be ignored by a thoroughly wedged computer that’s not servicing inputs. Which may still be happily commanding WOT with appropriate fuel flow and spark timing.
My belief is that by regulation current tech ICEs always have a raw hydraulic / mechanical connection between brake pedal & calipers. A computer might be able to trim or augment the mechanical pedal-to-master-cylinder output, but can’t completely ignore it. I can’t speak to the friction brake aspect of EVs, but I expect the same.
But that’s belief on my part, not certain knowledge.
I recall a fairly famous unintended acceleration crash that occured IIRC near San Diego. A Highway Patrol officer driving his family in a rented Lexus experienced unintended acceleration. They eventually faded the brakes to zero then crashed at 100mph+ and killed all 4(?) people aboard. My memory is hazy, but it seems the passenger phoned 911 to report their plight and included statements that neither the transmission selector nor the engine on/off button were responding to inputs. Was that operator error / panic? Certainly possible in an unfamiliar car. But this was probably a less than typically panic-prone driver. Offsetting penalties? You decide.
I think the outcome of the various lawsuits and investigations was floor mat jammed accelerator, but there was some evidence of Toyota skullduggerous investigation blocking that never came to much. All IIRC, and fuzzy IIRC at that.
Despite my scornful description of my guy upthread who blew up an engine for lack of knowledge about the “off” position of his key ignition I have a confession. I’ve been driving push-button engine on/off cars for about 6 years now. I have never tried to see what happens if I push the button while traveling down the road. I hope the answer is that after a couple seconds to resolve the implicit “are you sure?” question, the engine dutifully shuts off. And does so whether the brakes are applied or not. But I don’t know. It’s also good to know how the steering feels with a dead engine. There’s “stiff”, and then there’s “stuck/locked”.
I’ll fix that ignorance later today.
I’m not sure where you are, but around here, and from what I hear in much of the US, today is not the day I would choose for experiments on how a car would perform in outside-of-normal conditions.