Here on the internet people just explain the difference between the two and how you should also apply the handbrake when it gets steep, but why is there even a parking gear in the first place when you can just use the handbrake?
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2Interesting question. Especially from the point of someone one from Europe where most cars seem to use regular gears instead of automatics and the park position does not even exists.– HennesCommented Jul 8, 2019 at 15:59
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@Hennes It's so bloody flat around here, we just park in neutral and on the handbrake. Only on hills do we park in the gear reverse to the hill (if pointing upwards, in first, if pointing downwards, in reverse). And yes, that's assuming stick-shifted cars, there's not a lot of automatics around.– MastCommented Jul 9, 2019 at 7:25
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1I'm in New Zealand, where automatics are pretty much the standard (as per the US), and everyone I've just asked puts their automatic in park and applies the handbrake. They all thought it was dumb to just put it in park and not apply the handbrake. Thought you'd might like a view from a different country where automatics are the norm.– MooCommented Jul 9, 2019 at 10:03
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@Hennes: In a manual parked in (low) gear, the motor is directly connected to the wheels, and so can hold the car quite well. but in an automatic in D, the motor is connected via the torque converter, which is not a mechanical link. So, the motor itself can not hold the car. Though, todays automatics have a clutch for better fuel efficiency, but I don't know if it is engaged when the car is parking.– sweberCommented Jul 9, 2019 at 21:19
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3 Answers
Putting the transmission into "Park" engages the "parking pawl" - essentially a metal pin that locks the output shaft of transmission (and thus the driven wheels) in place.
As to why it exists - it is intended as additional roll-away protection that complements (rather than replaces) the handbrake (which, as the name implies applies actual brakes - usually to the rear wheels). The idea being that if either the handbrake or the pawl fails there's still something to prevent the car rolling away.
Handbrakes, like regular ones wear and thus become less effective with repeated use - and this isn't always immediately apparent to the driver so an extra safety net isn't a bad idea.
answered Jul 8, 2019 at 16:11
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5@motosubatsu complement not compliment - the handbrake is not polite to the gearbox... just for info, plus 1 from me... Commented Jul 8, 2019 at 17:54
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5@Peter An automatic transmission will never be secure while in gear with the engine off like a manual will. That's because of the torque converter. The pawl is the only way to lock the transmission in a fixed position.– LogarrCommented Jul 9, 2019 at 2:29
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3@davidbak yes those pins can shear through, and have done before... This is why the handbrake is the primary system and pointing the steering wheels appropriately is also advised. Commented Jul 9, 2019 at 5:40
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1@davidbak indeed..the "shock" you mention is the reason why the handbrake should be applied before engaging Park if you are on a slope. Commented Jul 9, 2019 at 8:51
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1@motosubatsu fair enough. I live in the Netherlands, where slopes don't exist :P– JADCommented Jul 9, 2019 at 10:49
Modern car systems also talk to each other - in more recent cars its impossible to start the motor while the car is in gear. So the gearstick has to be in Park or perhaps Neutral, perhaps with the brake pedal pressed or some other combination.
This is another safety interlock to stop a driver rolling on engine-start because the gearbox was left in a gear.
Of course there are very rare situations you might need to move/bump the car on the starter alone, which is now impossible. The classic Driver's Ed example was "stalled on a railway level crossing with a train coming and motor won't start"
Related How can I move my push-to-start car with the starter?
Also, by putting the transmission into park you're also telling the car its not going to move for a bit, so the computer may choose different courses of action for the engine compared to if you were simply stopped at a red light.
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3Well if the systems have learned to talk to each other perhaps is is possible that the gearbox really does -- as motosubatsu says -- compliment the handbrake. Commented Jul 9, 2019 at 0:56
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1@A.I.Breveleri so a possible message could be "piss off, I'm not ready", it would make the codes much more fun to read... :) Commented Jul 9, 2019 at 5:41
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For manual transmission cars: they often require the clutch pressed to start now, but don't care about gear. Commented Jul 9, 2019 at 11:21
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@cbeleites thats a design choice from somewhere. A simple manual gearbox should be in neutral and clutch out to keep flywheel engaged to add mass and help turn the engine over. My old landy likes that on cold starts.– CriggieCommented Jul 9, 2019 at 12:52
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@Criggie: first time I wanted to drive such a car I had to ask how to start it - I had automatically made sure the gears are in neutral and didn't even get to the idea that I should clutch (my experience with clutch in/out is mixed: mass vs. turning more stuff in cold transmission oil)... Anyways I think the design decision is OK for cars that automatically shut down the engine when standing (traffic light etc) - then taking the clutch as signal to start the engine again is quite intuitive. Commented Jul 9, 2019 at 13:10
The two options enable two completely different systems -- in principle, at least,
Putting your car in "Park"
This locks your central transmission into a fixed state, by mechanically freezing the clutch. (Exact approach on how that works depends on the specific model of car.) That means that your wheels are still free to roll -- even on a steep hill -- and you're relying on that transmission-locking mechanism to resist moving.
If you're on anything but a steep hill, then putting your car in "Park" is just fine. Period. Engaging the hand-brake is completely redundant. (And if your car is less than 20 years old, there's a good chance it wouldn't make any difference at all.)
Using the Parking/Emergency Brake
This is basically just a second brake pedal. Pulling on it engages the brake pads on each wheel, as if you were stomping on the brake. Locking it in place is pretty much the same as if you stomped down like that, and then just sat there like that for a couple of hours. (Again, the exact implementation completely depends on the specific model of car.)
If you're actually on a steep hill, then engaging the hand-brake is -- again, in principle -- a more reliable option, since you're now relying on your brake pads to stop your wheels from spinning at all. Those pads are designed bring your car to a screaming stop from 50+mph to zero in a matter of seconds. Asking them to resist the force of slowly rolling down any slope, no matter how steep, is trivial.
Key Considerations
Given all that, there are still some important points to keep in mind...
The underlying concepts of how a car "works" for these are so outdated that they're almost completely irrelevant. All of this guidance stems from a time that "cars" were purely mechanical systems, and questions of how to balance one system against another (like this one) really made a difference in the longevity and performance of a car. Modern cars are such complex, automated entities that this is all very likely moot for any car manufactured in the past 20 years -- I'd be pretty shocked if "putting the car in Park" and "pulling on the handbrake" aren't really just the equivalent of pushing the same button, two different ways, in most modern cars.
None of this is really valuable, compared to the most important single piece of advice for parking on a steep hill...
Curb Your Wheels.
Curb Your Wheels.
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I'm pretty sure that on my car (a 2016 Honda Civic LX), the "Park" setting affects only the front wheels, and the parking brake affects only the rear wheels. In particular, on an ice-covered surface, it is possible (but probably a bad idea) to drive with the parking brake set. The front wheels will propel the car forward as normal, and the rear wheels will remain locked. I don't have any particular evidence that the "Park" setting does not affect the rear wheels, but I think it would be awfully weird if it did. Commented Jul 9, 2019 at 3:06
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So much waffle, so much wrong. Did you even read the pages you linked to? Because even a cursory glance shows that they contradict your own inaccurate information. Commented Jul 9, 2019 at 9:02
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Well, you're wrong that park "freezes the clutch", wrong that the handbrake is redundant except on steep hills, wrong that it's the same as as second brake pedal, wrong that it applies to all the wheels, wrong in your stopping-from-50mph comparison, and wrong that engaging park is the same as pulling on the handbrake. You're correct in the usefulness of curbing your wheels I suppose. Commented Jul 10, 2019 at 8:39
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Then care to explain your view on how things actually work, @motosubatsu, rather than just yell at other people that they're wrong? Commented Jul 10, 2019 at 11:44