RH vs LH threads

My colleagues snapped off 3 wheel studs because they " were VERY tight" I looked at the stud end and pointed out they were left hand. I broke 2 more, as they were very tight, even with heating gear. It took me all day to get out the remnants and fit new ones. All good fun ! Noel

Lots of older vans and large cars had LH threads on the UK nearside. Rolls Royce are brass, and easily stripped with an air gun, as favoured by tyre fitters. The general explanation is that rotational panting of a steel wheel centre applied a differential torque to the conical seat of the nut, which would unscrew a RH thread on the nearside; the larger the wheel, the greater the potential problem. Now we have spigot mountings with flat faced nuts, so no need for LH threads.

Agreed (I was quoting Josie Dew).

You could also use the appropriate grade of Loctite.

I'm a bit surprised that this thread hasn't wandered off into abstruse explanations of the forces involved when a pedal unscrews itself, but I'm sure that our ancestors, being in the main classical thinkers, simply observed which bits dropped off and reversed the threads accordingly.

I've read Zen and the ... several times over the last forty-odd years, and always get something new and worthwhile out of it. It must be time to read it again. A friend who had studied philosophy at university dismissed it as lightweight, homespun philosophy, but I find it a lot more accessible than the classic philosophers. A bit like finding my way into jazz through listening to Chris Barber, when my serious (and scornful) jazz friend was into Charlie Parker and Thelonius Monk.

My 'hack' bike has a fixed wheel (not literally - it's the opposite of a freewheel) and the sprocket is screwed to the hub with a RH thread. There is then a lock ring on a slightly smaller LH thread which prevents the sprocket from unscrewing when I press back against the pedals to slow down. No abstruse physics there, but I do have a mangled hub from when I forgot that the lock ring comes off in the opposite dirtection.

George B.

I had the same thing when we studied metaphysics at school: it turned out to be a very complicated way of describing/explaining simple things, with little improvement for the effort.

In case it's not already been mentioned, the reason has to do with what's termed hypocyclic fretting precession.

Way back in the 1960s, my dad had a Plymouth car with LH threaded wheelnuts on one side. The local garage stripped one the first time they tried to take a wheel off, so they made a tap and a new nut in their workshop - I doubt many garages would or could do that these days. They gave him the tap, which I still have. Not sure if the stud was undamaged or if that was remanufactured as well.

Rob

My Bedford TK has both threads on the wheel nuts (not on the same nut!).

Years ago, I bought a Ballistic full suspension mountain bike frame. The bottom bracket had been welded on the wrong way round and on my first ride one side of the bottom bracket came loose. Fortunately I had self extracting bolts in the cranks and could tighten the bottom bracket enough to ride home. The bottom bracket, a Shimano XTR was treated to a little threadlock and gave no more trouble. Having right and lefthand threads counteracts the rolling forces which are present in bicycle cranks.

I believe that Italian bicycle bottom brackets have righthand threads both sides, so they may have a method of keeping them tight.

Zen and the Art of Motorcycle Maintenance?

Too much Zen, and not enough motorcycle maintenance, I thought when I read it as a teenager.

And he completely blew it for me when he's doing an oil-change and just lets the old oil run out onto the ground.

Quality, Robert, quality.

Traditionally, Italian (and French) fixed (RH) cups were indeed right hand threaded and, hence, were very firmly tightened when installed to prevent loosening in use. Left hand threaded cups were, presumably, self tightening and in consequence either kind are difficult to remove.

The subject is well covered by the Sheldon Brown website where, in particular, a DIY removal tool is described. The French call this kind of tool a "bloc-cuvette", literally a cup tightener but the phrase apparently also refers to the clip-on WC bowl cleaner!

Pedal bikes have clock- and anti-clockwise threaded pedals for a good reason?

And don’t forget that fittings on oxyacetylene are right handed for oxygen and left handed for computable gases

. Note the notch cut on the corners of the nuts to denote LH thread.

pete

I thought it time to ressurrect this thread. The choice of LH vs RH threads on a bicycle is done for good reason. Considering the pedals, RH thread on RH side, the often made assumption is that the pedal rotates CW on this side , it doesn't, it rotates ACW, the direction that will undo a RH thread. So why the RH thread?

A couple of the replies to my original question have "got it", what I am looking for is a simple explanation. So, once again over to you guys.

John

A pedal will indeed turn anti clockwise on its spindle, however the spindle is not totally frictionless so the force of a power stroke from the rider will tend to tighten it in the crank surely?

Hi John MC, here's my crude diagram of how I understand it. Notice the drag force on the pedal spindle is in the opposite direction to the resistance force, the resistance force is the resistance the road wheel has from turning, therefore a left hand thread on the pedal spindle will tend to tighten.

Regards Nick.

P.S.  If the pedal seizes onto the spindle you will find the pedal may well unscrew if it isn't rusted in, which has happen to me at least once, but I was young enough then to get home on one pedal.

Edited By Nicholas Farr on 29/03/2021 11:00:08

I dont think anyone paid any attention to your answer, or understood its meaning.

It's still the right answer though.

That's a little like the bloke who went to the doctor complaining of an itchy arse. Ah said the doctor you have a bad case of Scabrosa Asinum. What's that said the bloke. Err . . . . it means itchy arse in Latin replied the doctor. Huh said the bloke I came here for a diagnosis not a translation, I already know what to call it I just want to know what causes it.

:O)

regards Martin

I read The Book in the mid 70s, it seemed appropriate at the time. I am a technical person and have been all my life, I also understand the need for beautiful things, and beautiful design. F'instance, for me a 1957 Grand Prix Moto Guzzi 500cc is just about the epitome of pragmatic, elegant design. Of course there are examples wherever you look, but for me that 'Guzzi is perfect!!

cheers

Bill