Parking uphill without a curb - question

Simfish

Why would you turn the wheels to the right if parking uphill WITHOUT a curb as compared to turning them to the left if parking uphill WITH a curb? I've googled for explanations and none of them explain the physical processes involved, much to my frustration. Supposedly "If the vehicle rolls, it will go off the road rather than into traffic". Yeah, but wouldn't the uphill-ness make the car roll in the direction OF traffic (i.e. towards the left?)

Oh and would a free body diagram work? It's amazingly difficult to draw in the case of two axles+4 wheels. Oh - and an additional question - how do the back wheels steer?

stewartcs

Your quote explains it (assuming you drive on the right hand side of the road).

CS

Simfish

this quote?
it just says that it will move off the roadway if the car begins rolling - it doesn't explain how it moves off the roadway (especially since the wheels are pointed like // ) [and yes i'm using right hand side of the road]

rcgldr

The assumption is that if the front tires will roll into a curb and not over it. Ideally you want the front tires very close or slightly touching the curb to reduce any momentum.

Simfish

okay, sorry, I'm talking about the *uncurbed* roadways (where the wheels are supposed to point in the other direction)

stewartcs

If you are parked on a hill, and your car's parking mechanism fails, the car will roll off the roadway. The assumption is that something causes your parking mechanism to fail thus allowing the car to roll down the hill.

CS

Simfish

okay...

| | //|

car's wheels point in direction above. gravity pulls the car down. the direction the car goes SEEMS to be to the left (which is towards the roadway rather than off the roadway). How is this logic incorrect?

stewartcs

Because the back wheels hit the curb since the front wheel's angle steer the back of the car into the curb. The front end will move slightly toward the road until the back wheels hit the curb and stop the car.

CS

Simfish

Okay thanks. I think that explanation works.

"since the front wheel's angle steer the back of the car into the curb. "

okay does this mean that the back wheels automatically turn like \\ *as* the front wheels steer the car?

And how is this preferable to the other arrangement \\|? Is it more stable w/o the curb that way? (when it's the back wheels, rather than the front wheels, that are hitting the edge?)

stewartcs

The back wheels on most cars do not turn left or right, they stay straight. Some cars do though, Honda used to make a Prelude that had "All Wheel Steering" but thats not the norm.

It all comes down to the simple idea of "blocking" the wheel against the curb to prevent it from rolling. So, if you don't have a curb, there is no "stability" as you say. The wheels are just positioned to prevent the car from rolling out into traffic.

CS

LURCH

Try getting in a car, turning the wheels to the right, and backing up. The front end swings out into traffic briefly, but overall the car goes right, and off the side of the road. When I took Driver's Ed. ( along time ago), we were taught to turn the wheel to the right whether there's a curb or not. If you turn to the right and there is no curb, the car goes off the road, if there is a curb, the back wheels will hit it and either stop or go off the road.

Seems to me the way they teach it now is not so good. With a curb, you point the wheels left, and as the car rolls back the front tires hit the curb. Maybe the car stops, but maybe it backs sidewise right across the road!

swraman

Yea thats exactly the way I imagine it too. I remember wondering this too when I took my drivers test.

Well, i stretched my art abilities, and heres my attempt at a diagram (imo they always help):
http://thenorthstaronline.com/raman/images/cars.bmp