The Mystery of Left-Hand Lug Nuts

The next time you’re hanging out with your buddies and discussion turns to the many unique engineering details found on our Mopars – things like torsion bars, Super Stock leaf springs and ram tuned induction, ask the question: “What’s up with the left-hand lug nuts used on the driver-side of the car”? I’ve been involved in countless discussions on this topic and have heard a wide variety of theories over the years ranging from the absurd to the probable.

On the absurd side, some say one of Chrysler’s fastener sub-contractors screwed up (pun intended) with an un-related industry customer and cranked out several million left-hand studs and nuts when the order called for standard right-hand threads. Chrysler supposedly got a screaming deal on a zillion parts and adopted the fasteners for production until the supply finally ran out in 1970.

A somber looking affair, the 481 page Passenger Car Safety Dynamics was first printed in 1965 with subsequent printings in 1966, 1967 and 1968. Don’t look for it on the New York Times Best Seller List. This one is from the fourth print run of August, 1968.

Another theory that’s bandied about like a beach ball is the idea that Chrysler sought to punish customers for taking their Chrysler Corp. vehicles to non-authorized service stations. Unless these independent mechanics were hip to the Chrysler left-hand way, they’d never get the wheels off and become discouraged. They’d assume that working on the rest of the car would be just as problematic. In disgust, they’d call the customer and say something like: “Get it outta here and take it to the dealer”. The notion that Chrysler would take this passive-aggressive deterrent strategy sounds crazy…it is.

More thoughtful theories have a lot to do with the physics of a rotating wheel and the effect of inertia and centripidal force on the threaded retaining fasteners at high speed. Let’s take the example of sports cars fitted with knock-off wheels. If you aren’t familiar, knock-off wheels do not use typical wheel studs and nuts to retain the wheel on the brake hub. Instead they have a central splined-hub onto which the wheel fits. Then a large spinner is threaded onto the hub to lock the wheel in position. Tightening (and removal) is accomplished by striking the blades of the spinner - with a soft brass or lead hammer so the chrome finish isn’t deformed by the blows.

You’ve probably seen knock-off wheels on Jaguar E-Types from the Sixties as well as certain 1963-1966 Corvettes. The functional benefit is that you can remove and replace wheels and tires very quickly in pit-stop situations during a road race or other timed competition event. By contrast, fiddling with a handful of lug nuts would add precious seconds to the pit stop – don’t tell that to NASCAR.

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