On Top Gear, they regularly end up spinning cars 180 degrees or more while test driving. Almost every time, the car ends up drifting backwards (on it’s wheels, so it looks like just normal reversing) for a short distance before coming to a stop.
How is it that the wheels can go from propelling the car at 80+ mph (on a slow run) to spinning in the opposite direction in under a second, without tearing apart the drivetrain?
You missed the point. If the car remains in a forward gear, the car may have momentum “backwards” after the spin, but the wheels most certainly won’t be allowed to go “backwards”, without some serious damage to the transmission…
Any driver would hit the clutch to save the drive train.
It behooves the automatic clutch (however implemented, whether stick or paddle, single or dual, or whatever ) ones to do that too.
A classic automatic , with planetary gears, has a torque convertor, which , apart from altering the torque rpm curve, allows rolling backward even when in a forward gear. The car might have anti-rollback for hillstarts, but thats just an idle speed adjustment, not much !. and antiroll back is probably turned off when stability control is off, or when stability control is operated.
I’d guess that most people that drive stick would jump on the clutch out of habit. It’s a nature thing to do anytime things go weird. You learn pretty quickly if you don’t hit the clutch the engine dies (yeah, I know lots of exceptions).
While the torque converter, being a fluid coupler would would allow the car to roll in the wrong the direction. You’ll also notice that often times after a car spins out, the engine isn’t running anymore. It’s my understanding that that’s because instead of the engine providing power to the wheels, the wheels are now providing power to the engine and trying to spin it the wrong way. I assume that slows it down and screws with the timing which shuts it down.
Also, as I think about this, if enough oil gets sloshed into the wrong place, the drop in pressure will kill the engine. (Old cars (at least the Fords I had), had some kind of sensor that would kill the fuel pump in the event of an accident, newer cars have the fuel pump inline with the oil pressure sensor and use that to detect a rollover).
Without depressing the clutch or putting the car in neutral the tires will help stop the car. But if the car is rolling backwards then the wheels are no longer trying to drive the car.
I did not miss the point.
Okay, that’s what I couldn’t get my head around: drivers (even highly experienced ones like the presenters on a car show) recognizing the situation, considering their options, and choosing to apply the clutch (along with other actions), all in under a second.
You can’t get your head around how they can do it that quickly or why it works?
Why it works was mentioned up thread, it’s just momentum.
As for how to do it that quickly, I’m guessing you don’t drive stick. At least not on a regular basis. “recognizing the situation, considering their options, and choosing to apply the clutch (along with other actions), all in under a second”, is no different than you pouncing on the brake pedal because someone walked out into traffic. You don’t think about it, you just do it. If you’re driving stick, that left foot is always ready to hit the clutch if there’s an issue.
In my experience as a performance driving instructor, people instinctively push the clutch for whatever reason, and completely forget about the brake. Usually the car has already stalled by this point, but often they’ll still be on the gas as well. Clutch + brake in a spin has to be taught and practiced.
This can cause a real problem at performance driving events, where people be holding down both pedals not realizing that the gas isn’t the brake, meanwhile rolling slowly backwards across the track and into the line of traffic. Hence the mantra.
As noted, the correct spin recovery procedures may not be intuitive, but instead must be thoroughly practiced until they can be done immediately and without having to think about it for a while.
This has some analogies to flying airplanes, which can also “stall” and “spin”. (For rather different definitions of “stall” and “spin” than car drivers may be familiar with.) Here likewise, the most instinctive things to do to recover are exactly the wrong things to do, and can lead to results much more grievous than trashing your transmission. Correct recovery must be practiced until the right steps become immediate and instinctive.
Even more importantly, the correct steps (which are not exactly instinctive in some cases) to prevent stalls and spins must be taught and beaten into pilots’ heads while they are still student pilots and practiced until they become instinctive.
I’ve read that stalls and spins while in the final stages of landing an airplane (which are almost always fatal) account for 60-some-percent (or is it 80-some-percent?) of all in-flight airplane accidents. When it happens so close to the ground, recovery is rarely possible. Prevention is paramount, and certain moves the pilot may “instinctively” make are exactly what cause these accidents.
It is said that student pilots make these errors the least often, as the dangers as well as the correct procedures are beaten into our heads early and often. It’s the more experienced pilots, when they become lazy and complacent and sloppy, who most often wipe themselves out (and their passengers) this way.
Something to add, when it comes to driving stick, is that the clutch becomes very, very second nature. You watch a new stick shift driver kill the engine constantly. Then in an attempt to not kill it they take off down the road at about 90 MPH, for 6 feet, panic and kill the engine. They roll backwards down a hill from a stop, kill the engine etc. Eventually they learn to feather the clutch and within a few days/weeks, they can not only go from stop to getting up to speed as fast as any other, they can often do it faster than the other cars.
Similarly, you can watch a new driver have the car lurching (for any number of reasons) from a stop and either panic and kill the engine or panic and put the clutch all the way in and really have to think about what to do from there (which is even more panic inducing in an intersection). But after a while you get so used to it, you can feel that ever so slight rumble as you take off, put the clutch back in just a hair and let it back out. You can just do it.
Even after 20+ years of driving stick, one of the things I still love hearing, after driving around at night is getting out of the car (and the dome lights come on) and the passenger(s) says ‘this is a stick shift car, I didn’t even notice’. But then I tend not to wind it up too much.
The person that gets into an automatic car and puts their left foot on the brake (or invisible clutch) to start it…the person that once in a while accidentally throws the car into park (well, shoves the gear shift up, so I guess it lands in neutral) as they coast to a red light; those are the people that have been driving stick for long enough that not only can they hit the clutch during a spin out, they wouldn’t think anything of it. Like I said earlier, it really is no different than you hitting the brake because someone walked out into traffic. That is, something is wrong, you hit the brake. For me, if something is wrong I hit the brake and clutch (of just the clutch).
And just to reiterate. Over simplified, you often hit the clutch and brake together, especially in a panic stop. In a spin out, you wouldn’t have to think about it, you’d just do it.
I’m missing something. Why can’t an automobile engine spin backwards, if it’s the momentum of the car driving it?
Yes, you couldn’t operate the engine backwards and get power out of it. But there’s nothing to keep you from forcing it backwards. It would pump air from the exhaust system backwards and out the air cleaner. Why would that work much differently from when you’re driving normally down a hill with your foot off the gas, letting the drag of the engine hold the car back a little?
You CAN spin a car engine backwards. In many cars, you can just start the engine again and be fine.
It occasionally happens that if an engine is dieseling, it may do so backwards. Apparently having the valves opening and closing at the wrong points in the cycle doesn’t necessarily foil this spectacle.
If there is a timing chain with a tensioner on what is normally the low tension side, spinning backwards makes that the high tension side and may move the tensioner, making the chain loose or even letting it skip. This can damage an “interference engine”, meaning an engine in which the valves and pistons take turns occupying the same space. Only the cam timing keeps these expensive parts from colliding in a most forceful and emphatic way. With the timing spoiled, the engine can beat itself to temporary death in a moment.
This, and remember all the people in Top Gear (old and new) have gone through many performance driving classes and are very experienced and skilled drivers (yes even captain slow). Spin starts, clutch and break, release break when until control clutch is still down -> end up rolling “backwards” .