I've been told that reverse is the "strongest" gear, so in a manual transmission vehicle you should park your vehicle and leave it in reverse in the event of a parking brake failure. Others have said first or second gear are fine as well.
Is there a "best gear" to leave your manual vehicle in when parking it?
The lower the gear, the better the job the engine compression will do at holding the car if the brake fails, that's because a lower gear makes the engine spin faster and requires it to do more work for the car to move. So 1st is better than 2nd, between reverse and 1st it's not so obvious – but from the examples people are finding it looks like 1st is a bit better.
Bottom line, 1st or reverse, leaning towards 1st.
When I'm on a hill with the front of my car facing up the hill I park the car in first and turn the wheels away from the curb so the transmission is fighting against gravity.
When I'm on a hill with the front of my car facing down the hill I park the car in reverse and turn the wheels into the curb so again the transmission is fighting against gravity.
When I'm on flat ground I park in first as reverse is too finicky to deal with that frequently :)
Happy to be wrong here. Just what I've always done - opposed the forces of gravity with the opposite transmission gear.
So, looking at a couple common manual transmission gear ratio charts, first gear would be best. Why? It has the highest ratio. Although it is (in the charts I found) very close to reverse.
Here's a chart for Honda Civics (up to '91 I think)
Here's a PDF from Toyota's press room with their Corolla specs.
Highest ratio = greatest amount of torque applied to the wheels from the crank. Conversely, more torque needs to be applied to the wheels to force the crank to rotate. Also, from my understanding, the forward or reverse gears make no difference except that (I imagine) your motor REALLY won't like being rotated backward. So in that regard maybe it would be better to choose the gear that suits your hill directionality... but at the same time, if you brake and trans fail to hold your car on a hill, chances are things could go VERY wrong very quickly.
First gear when pointing down hill, reverse when pointing up. If your car ends up rolling, the engine will turn in the correct direction. If you park in reverse pointed downhill and your car rolls the engine will turn backward, and vice versa. This can cause various problem with the engine including skipping a tooth or binding on the timing chain/belt and is almost universally cautioned against when working on engines.
That's what your parking brake is for.
It's called a parking brake for a reason. If parking on a steep incline, turn your wheels so that your car will roll against the curb if the brake fails. Better yet, as the last step when parking, let the car roll (gently!) against the curb already.
If you use a gear to keep your car from rolling, that puts a strain on the engine and the entire drive train for which it wasn't designed. Specifically, a mechanic at my local garage described it as "hanging on the cam belt", which would lead to greater wear on it.
You certainly want either neutral, 1st or reverse (depending on circumstances, see other answers). One aspect that I see influencing this is a gearbox lock - some cars have an anti-theft feature that can lock the gearbox, preventing the thief from shifting. On such cars, reverse is preferred, as it makes it much harder to drive the car away.
I have an alternate suggestion for using reverse with a stick shift to park. Perhaps merely to facilitate backing out of the parking space. In first gear you increase your odds of ramming into the curb if momentarily distracted.
ok a real answer first that doesn't rely on special conditions
if you are pointing uphill put it in reverse. this is to prevent any damage from rolling because you have a house in San Francisco. you should also steer the front wheels to the left (right if you're british) so the back of the front tires are effectively chalked by the curb.
if you are pointing down hill then it should be first. you should also steer the front wheels to the right (left if you're british) so the front of the front tires are effectively chalked by the curb.
now for some conditionals
1st gear, low range 4wd, diffs locked, under drive engaged, and axles set to low gear. yes this does give you 3 shifters and 2 buttons. more is better right?
To add an answer with sources, I own a Hyundai i20. Page 5/4 (191 of pdf) of the owner's manual states:
Before leaving the driver's seat, always make sure the shift lever is engaged in 1st gear for manual transaxle or P (Park) for automatic transaxle, set the parking brake fully and shut the engine off. Unexpected and sudden vehicle movement may occur if these precautions are not taken.
Page 5/8 (195 of pdf) states:
Before leaving the driver's seat, always set the parking brake fully and shut the engine off. Then make sure the transaxle is shifted into 1st gear when the vehicle is parked on a level or uphill grade, and shifted into R (Reverse) on a downhill grade. Unexpected and sudden vehicle movement can occur if these precautions are not followed in the order identified.
I'd rather take my advice from the manufacturer of the vehicle!
The lowest gear to go up the hill. Lowest for mechanical advantage (you are using compression in the engine as the force). Up the hill as that is the direction of force the transmission is designed for. So first if pointing up the hill. Reverse if pointing down the hill. Level ground reverse as reverse gets less wear and tear in normal use and it is also typically a lower gear than first.
Habitually leaving a manual transmission car in gear is a bad idea. One day you will jump in the car, turn the ignition, and discover that the starter motor is more powerful than the handbrake (you will start moving before the engine even fires!), but the object you just hit was stronger than the car.
Automatic transmissions may have a lock that prevents you starting the car when the transmission is engaged, but (at least in the UK and Europe) manual transmissions do not.
