I had a couple of old jeeps which used lefthand threads on the lugnuts on the right side of the car. I understand that Chrysler cars used them well into the 70s.
Why?
I always had to remember “righty loosey, lefty tighty” on that side of the vehicle.
to prevent the mechanical forces acting on them from loosening them.
a taper on modern ones prevents that and allows right handed threads all around.
From what I’ve heard, it is like this: The vibrations on the left side of the car tend to make the nut want to go clockwise, and that’s okay for a normal thread. But on the right side, the vibrations will make the nut try to turn counterclockwise – too much of that and a normal nut will fall off! So they reversed it.
I have no idea how accurate that is. Nor do I understand what it is about the vibrations that would favor one spin over the other. Apparently, the top of the nut wants to go toward the back of the vehicle, and the bottom wants to go to the front, regardless of whether it is on the right side or the left. Makes no sense to me.
It has to do not just with “vibrations,” but the spin of the wheel. The lug nuts tighten in the direction that the wheel spins.
That started to make a LOT of sense, but maybe I was overthinking it…
Let’s take the simple case: the normal thread on the left side of the car. When the wheel starts to turn, it is going counterclockwise, so the nut which is not yet turning, and tends to stay motionless, ends up getting tightened. Great, fine, thank you. But doesn’t that get reversed when decelerating? The nut wants to keep on turning, but the wheel is stopping, so why wouldn’t the nut get thrown forward – i.e., loosened? Wouldn’t these two effects tend to cancel each other out - for both sides of the car, no matter what sort of thread it has?
(I hope everyone understands that when I use the phrase “wants to”, that’s just street talk for “the laws of inertia dictate that it will tend to”.)
Semis still have that.
Used to be standard on truck wheels over here.
All british built trucks and buses had left and right hand wheel nuts until about 1980. Left hand were on the left side, and were tightened in the direction of the wheels rotation so they would not work loose in operation. They were known as coned wheel nuts because the had a taper on the end of the nut that sat in a recess in the wheel. In about 1980 they moved to spigot wheels where the wheels locate on spigots on the hub preventing the wheel from working loose.
No. Lug nuts, like the One Ring, have wills of their own.
in the vein of the general topic
I remember reading an article a few years ago about some college inventing/discovering threading with a sinusoidal shifting turn out to handle vibrations better, not un-screwing as easily
FWIW, bicycle pedals still work this way.
As I see it, that’s very different than the car wheels. On a bicycle, the rider is constantly pushing in one direction, and almost never in the other direction. On a car, the acceleration and deceleration are equal and opposite, and would cancel each other out.
The loosening is due to the wheel shifting slightly as it rotates while supporting the load. This is the same direction regardless of acceleration or braking forces. The only time the nuts would tend to rotate in the opposite direction is when rolling in reverse, which is minimal.
Bicycle pedals are threaded to resist precession rotation, not torque due to bearing drag, which would require opposite threading.
To observe precession, make a loose fist around a pencil. Crank the opposite end in a circle, and observe how the pencil rotates.
Don’t think just of the torque during acceleration and deceleration: Those will, indeed, roughly cancel out. But even for a vehicle going at a steady speed down the highway, you’re still continually applying a torque to the wheels, and you’re applying it through the nuts.
THAT is an answer that makes sense. Thank you.
My cordless circular saw and most mitre saws use reverse threaded arbors to prevent torque induced loosening. They usually have a arrow indicating proper loosening rotation.
Every vehicle that I have come across with left handed thread had them on the left side. This would include many Chrysler products, a Hudson and a Henry J.
The left pedal and often the left side of the bottom bracket assembly (that’s the part with the bearing between the crank arms.
We can thank the Wright Brothers, yes those Wright Brothers, who came up with the idea of left-handed threads to combat the problem of the left pedal unscrewing while riding.
Now with better threading and bearings, it’s probably no longer a real issue, but it would cause a lot of problems changing it. Manufacturers would need two different threaded left pedals and bike mechanics would have a learning curve.