I think you'll find quite a lot of vehicles have LH threads on that side Leon. Seems to be mandatory over a certain tonnage or type of vehicle. Only one I ever drove at work was a Mazda T3500. Running empty it had horrible vibration due to the harder springs, probably the reason for the LH threads as a bit of fretting of the locking surface could make them loose enough to start spinning off. Just a guess.
LH threads were on cars up til' the 50's. The car wheels after that era were designed to "spring lock" the nuts. That is why cars are all RH threads now.
Truck wheels are heavier and it can still be successful but various country legislation demands the additional safety of LH threads.
Left hand threads on car wheels probably save a lot of lives in the early days. The natural flexing of the wheels, that were supported by the studs only, meant that there was a tendancy to slowly undo the nuts on that side if they in any way loosened if the thread was RH when the car was travelling forward and once it started it would only be a couple of miles before the wheel came off.
Large vehicles are subject to high temperatures on the wheel hubs. This can loosen the nuts. LH threads are self tightening (due to precession.)
Race cars often have the two different threads as well.
Sometimes after changing a wheel, and even though the nuts are tightened, they will loosen after 150 Klms. Usually after long periods of heavy braking.
Early cars were prone to losing wheels, until manufacturers installed LH threads. There were many fatalities from those accidents in the early days.
My Honda CX500 m/cycle had a left handed bolt holding the fan blade onto the end of the crankshaft. As it is self tightening, the fan blade would never work its way off.
Large vehicles are subject to high temperatures on the wheel hubs. This can loosen the nuts. LH threads are self tightening (due to precession.)
Cheers
I like that precession explanation. That is exactly what causes the orbital creep of the wheel stud on the nut and wheel as the load application changes while the wheel rotates.
Barry
Last edited by Barrykgerdes; 12-07-2012 at 03:32 PM.
