# Parallel parking physics

Why is it easier to parallel park by backing in than by pulling in? It’s the same car & the same space. What’s the difference? A wide variety of smart people haven’t been able to explain this to me. The best answer I got was “it’s a different angle.” That explains nothing.

It’s easier because steering is controlled by your front wheels. This means you have more precise control over the front of your car than the rear. You want to do the final “squeeze” going forward, not backward.

It sounds like you’re arguing that it’s symmetric either way, so it should be the same. But it’s not symmetric - a car’s front wheels can steer, which makes all the difference. You want those to go in last. If you go in front-first, your rear wheels couldn’t get any closer than a half-car-width from the curb, unless you go back-and-forth several times. If you go in first with the fixed (non-steering) wheels, you can get those right up near the curb, then steer the other wheels next to it, all in one pass!

It’s the fact that the trailing wheels (the front wheels if you’re backing in) are steerable.

If you pull in or back in, you can only get to a certain point before steering. Having the end that’s coming in last be maneuverable is what makes back-in parallel parking easier.

It’s this same reason that extra-long fire trucks have steerable rear wheels; so that the truck as a whole can maneuver into tighter places.

Find a big parking lot with a puddle in it. Drive through the puddle and then turn the steering wheel all the way left or right until your car drives a full circle. Then stop and look at the tire tracks your wet tires left. The front wheels draw a bigger circle than the rear wheels (at least at slow speeds they do. If you’re parallel parking at 60 miles per hour, there are other issues we have to deal with). The same thing happens if you come too close to a curb when making a turn, the front wheel just misses the curb but the back wheel rides up and over. When driving forward, you steer the front wheels where you want them and the rear wheels take a short cut and fall into line behind them. But if you pull into a parallel parking space front first, you can’t drive forward far enough for the rear wheels to come into line.

And the same thing works in your favor when you back into a spot. If you try the parking lot experiment again in reverse, you’ll find that the front wheels still draw a larger circle than the rears. When you’re backing into a spot, you get the back end of your car aimed where you want it, back up until you’ve cleared the car in front, then crank the steering wheel hard over. That makes the front end swing wide (outside the rear wheel tracks), which is just where you want it.

It’s really easy to visualize the reason for this if you imagine getting out of the parking spot. Say you’re parallel parked two inches from the curb, with cars in front and in back. If you drive out front first, you can basically turn the wheel as far as it will go and drive out. However, if you try to back out, your front wheels will hit the curb if you turn too sharply, so you have to take a more gradual curve.

Now, videotape that and play it backwards. That’s why you back in.

Lots of correct but slightly unsatisfying answers.

Imagine a front wheel drive car with wheels that can turn 90%. You could back in at an angle until your back wheel is at the curb then rotate the front of the car in without moving back at all.

90%? What in hell was I thinking. 90 degrees, sorry.