Should you put the car in gear before or after you turn the car off? Obviously when parking uphill I leave the car in first, similarly when parking downhill I leave the car in reverse and on both I pull the parking brake.
If, when parking and placing the engine in gear before turning off the ignition, there is an infinitesimal chance that you will be distracted or hit by a meteorite and let your foot off the clutch while the engine is running. The manufacturer's lawyers told them to put it in the owner's manual to reduce their liability.
I do a little bit of both really
I usually put it in gear after pulling the brake, and after the car is off. I don’t know if it really does much, I’m sure the folks here may know the mechanical answer. It’s kinda what I was taught, and I hope what I’ve been taught was the right way, because it is habit now.
It sounds like you're talking about manual transmission. I don't think it really matters. If reverse gear has no synchronizer it can be easier to turn the engine off first. (Also some cars with stick shift won't let you withdraw the key unless left in reverse regardless of whether on an uphill or downhill slope.)
Why is that? Wouldn't it be more beneficial to have the car in first when parking uphill and reverse when parking downhill?
The engine offers sufficient resistance either way that it doesn't really make any difference.
consult your vehicle's owner's manual
My owner's manual says turn the car off, pull the parking brake, and leave it in either first or reverse. However, I was just wondering if it mattered.