Wheel Nuts - Right Hand and Left Hand Thread

[balangproject]

From my understanding current F1 cars have a left-handed thread on the right side of the car and right-handed on the left. I have a vague understanding of why this is but I can't find any technical information to fully understand why it's a positive locking mechanism.

I'm a mech eng student working for a Formula Student team and we're deciding whether we should use left-handed threads on one side, after seeing that F1 uses them we thought about adopting it as an extra failsafe.

For the right hand side rear wheel I can see how a left-handed thread would help as during acceleration the right side power is delivered in a clockwise motion, the wheel opposes this in an anti-clockwise moment and as the wheel nut is fixed to the wheel this results in the wheelnut forcing in an anti-clockwise motion thus tightening a left-handed thread. But during breaking on the front right side you would expect the opposite, yet they are left-handed thread aswell.

Any thoughts?

[olefud]

Maybe not the same, but during the 1960's Pontiacs had left and right-hand lug nut threads. This was suppose to prevent precession unscrewing the nut as the round fastener and round hole rotated with resulting fretting. With the taper on lug nuts, it's not really necessary. My guess is that in F-1 they want the precession to be oriented to tighten the nut.

[Jersey Tom]

If you make the assumption that braking torque will be greater than driving torque, it makes sense.

That said, on a FS car the easiest and most practical method would be to use a big "castle" wheel nut with a pin through the hub. That's a SOLID fail safe.

[andylaurence]

I run the same thread on all four wheels with a pin preventing each nut from escaping. Provided you use the right torque to tighten, I see no reason you will have a problem. If you do, the pin is effective - don't ask how I know!

[olefud]

If you make the assumption that braking torque will be greater than driving torque, it makes sense.

Precession is primarily a function of direction of rotation. But there's also inertia working on a nut on the end of the axle. I wouldn't sweat either in the application in question.

[balangproject]

If you make the assumption that braking torque will be greater than driving torque, it makes sense.

That said, on a FS car the easiest and most practical method would be to use a big "castle" wheel nut with a pin through the hub. That's a SOLID fail safe.

This is precisely what we were going to have aswell.



Anyone know the theory as to why a left-hand thread on the right side of a car is correct?
If its axial force alone then it shouldnt make a difference what thread you have, so im guessing its the relative rotation of each component (wheel with hub etc..).

[olefud]

I'm not sure of the actual structure; but I assume that the axle and nut are not rotating (pretty safe assumption). Thus there is a thrust bearing between the rotating wheel and the securing nut. The thrust bearing would have some drag which in turn would exert a torque on the nut, clockwise on one side and counterclockwise on the other.

Or, with a bit more mass and/or a slight weakening of the axle, the thrust bearing could be pinned to the axle and there's some other reason.

[Jersey Tom]

Anyone know the theory as to why a left-hand thread on the right side of a car is correct?

As I was getting to before, assume that braking torque is the dominant effect here (outweighs drive torque). Will tighten everything.

[xpensive]

With all due respect to everyone, I find it dfficult to believe that the wheel-nut's inertia would play any role here, neither during acceelleration nor its opposie?

[strad]

In the olden days before you guys were born, Chrysler products had the lug nuts that way.
"I" think it goes back to Knock Off wheel nuts...
Those if I recall my early sporty car days correctly were right and left hand thread because before they did that, they DID loosen in use. And even then they wailed on them with a lead hammer.

[Jersey Tom]

With all due respect to everyone, I find it dfficult to believe that the wheel-nut's inertia would play any role here, neither during acceelleration nor its opposie?

Correct. Inertia has nothing to do with it.

[xpensive]

With all due respect to everyone, I find it dfficult to believe that the wheel-nut's inertia would play any role here, neither during acceelleration nor its opposie?

Correct. Inertia has nothing to do with it.

So, what is this thread about then?

[Jersey Tom]

When you torque the wheel nuts and send the car on it's way, there will be a fair amount of contact force between the nut and wheel. My understanding of the concept is that under braking, if there's any slop between the wheel and the drive studs that allow the wheel to rotate a bit... there is enough friction between wheel and nut to drag the nut in the direction of rotation and self-tighten it.

Either way, the amount of slop there is likely going to be small and the effect probably isn't huge. And in any event, I know that current era pro open wheel cars have positive locking mechanisms on the hub & nut to prevent any rotation and all. That is still the most effective fail safe, and the mechanism only unlocks when the impact gun goes over the nut.

[xpensive]

Aha, like over-torqueing the nuts on one side of the car and loosening them on the other due to the rim slipping when braking?

Never crossed my mind actually, but if the friction between nut and wheel overcomes thread-friction, then I guess that could happen, but how much is the clearance in the drive-studs then?

[Jersey Tom]

Aha, like over-torqueing the nuts on one side of the car and loosening them on the other due to the rim slipping when braking?

Right. And by flipping the thread direction on one side, you make them ALL tighten under braking. Now you can make the argument that drive torque will want to loosen them, but we can pretty safely believe that aggressive braking events are going to be more severe than driving.

Anyway, there probably isn't much slop between the drive pins and wheels, so I don't think the effect is that great. The positive lock is the more effective thing.