Re: Left hand threads on near side wheel studs?

I've just come across a case of a Mazda van with all the wheel studs

> on the near side having left-hand threads. All the offside studs are > normal thread. How unusual is this? BTW there is no mention of this > in the Owner's Manual.

You are so lucky! Mazda are doing things right! Have you ever noticed that bicycle pedals have opposite handed threads on opposite sides of the bike? The problem that this avoids is called "precession". If the threads were the same on both sides of the bike one pedal would unscrew itself!

Similar things can happen on motor vehicles and trailers. The precession p roblem is worst on "lug-centric" wheels. These are wheels which are a slopp y fit on the hub and rely on the wheel nuts to center the wheel and carry t he weight.

The more modern type of wheel is "hub-centric". With this type of wheel an d hub the hub spigot is a snug fit in the wheel. One minor snag is that af ter a little rusting has taken place removing the wheel may need a hydrauli c puller! With such a good fit one can surmise that the spigot carries most of the weight. Precession does not seem to occur to any great extent on t his type of wheel as the nuts are just clamping the wheel in place instead of carrying the weight.

IMHO lug-centric wheels can give a lot of trouble on the left hand side of vehicles (especially on heavily laden trailers) One good modification is to fit longer wheel studs that will accept a Nylock-nut on top of the wheel n ut. Thread lock is another get-you-home method if the nuts loosen persisten tly. Superglue is also extremely effective! Good luck!

Reply to
david.benyon
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Given that just about every car ever made with nuts and studs or bolts rather than centre lock uses only right hand threads, it can't be much of a problem.

What is a problem with left hand threads is the average tyre shop trying to undo them the wrong way and damaging the threads. But of course simply putting them back on, rather than admitting to this.

If you think about it, only a fixing which is concentric to the axle is going to be affected by the direction of rotation - not one which is offset from that centre line.

Reply to
Dave Plowman (News)

That'll be why they don't bother with LH nuts on trucks, then. Oh, wait...

Reply to
Grimly Curmudgeon

That'll be why all cars have them too, then?

Oh, wait...

Reply to
Dave Plowman (News)

Much less of a downside to a car wheel coming off and generally, if you fit LH nuts to one side of a car, there will be the numpty problem cropping up all the time.

Reply to
Grimly Curmudgeon

Really? Isn't that a bit of a generalization? And either it is a necessary thing or it isn't. Regardless of the type of vehicle.

I can understand a centre lock wheel having a handed thread. But one secured by studs and nuts or bolts? Complete rubbish. There is no undoing or self tightening moment on that type of fitting.

The reason trucks still have left hand threads is likely history. For the same reasons cars don't. Change what is the norm and an unskilled mechanic could cause more problems than the use of them was meant to solve.

Reply to
Dave Plowman (News)

Yeah but, I think you're much more likely to be aware of the clonking of a loose wheel on a car than the driver of an HGV might be to a loose wheel on his trailer say.

I wouldn't be so sure. If a wheel is a little bit loose I could see how a wheel moving around on the studs could impart rotation to the nuts

Maybe, but maybe also for the reasons Grimley gave, namely the consequences of a lorry wheel coming off are potentially far graver (and potentially more likely to happen if the driver can't hear loosening).

Tim

Reply to
Tim+

Since the wheel can't turn relative to the studs, how does it loosen the nuts? You might as well say a wheel on the other side which was loose would tighten the nuts - and this certainly doesn't occur. Any movement due to a loose fixing tends to loosen that fixing even more - unless it is concentric.

Doesn't seem to be adequate given they are also fitted with indicators. If the nuts self tightened, there'd be no need, would there?

Reply to
Dave Plowman (News)

Nuts and bolts on flange joints can unwind if there are out balance loads. Loads that overcome the friction in the flange joint to the hub. Page 15 on.

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Yes it would have to be so bad you would think that the owner would do something about it but ...

My mates wife had driven 1000's of miles in her car before they used it for a night out. He instantly knew from sound and vibe during braking he was going to be replacing a cracked disc and pads that weekend. "Oh it's been doing that for some time". He learnt he had to test drive her car a bit more often.

Reply to
Peter Hill

Rather than spouting crap how about trying an experiment (as I have just done). All you need is a nut, bolt and a large washer.

If the nut isn't tight just oscillating the washer in a circular fashion on the nut (without ever rotating it) as would happen with a slightly loose wheel, will cause the nut to turn.

Tim

Reply to
Tim+

If the nuts are loose on a wheel it's not going to make any difference what hand they are. The argument is whether correctly tightened nuts are more likely to come loose if not handed.

Unless you're saying they will self tighten?

Of course I'm not speaking from experience. Despite having driven perhaps hundreds of different vehicles, I've never had a wheel come loose. Those who have perhaps need to check such things themselves rather than leaving it to a garage.

Reply to
Dave Plowman (News)

I've seen it happen once. It was in autumn 1954, I was 5 years old. Walking to primary school along the pathway beside a road, curving gently to the right, there was a scraping noise behind me and I turned to see the left hand front wheel of a car rolling along the road generally towards me. The car had stopped, scraping its suspension on the road.

The wheel passed in front of me, crossed the path, and fell into somebody's front garden. I noted it was one with silver spokes. The car was I think a Singer sports, mainly white, an old style even then, with running boards.

I thought nothing more about it until many days later, when my father was changing a wheel on his car. I tried to lift the spare wheel upright, and found it too heavy for me. I then realised that if that sports car's wheel had hit me it would probably have killed me!

Reply to
Graham J

But most wire spoked wheels back then were knock on with a single centre nut. This is about 4/5 wheel nuts/bolts on a hub flange.

Reply to
Peter Hill

Really, you should get out more. It's happened to me twice, both occasions thirty years ago and I suspected foul play. However, rural back roads, no ped, no traffic and no real drama. At 40mph, the rear right wheel detached, the car sat down and rumbled along on that corner (drum brakes) and the wheel overtook me, bounced as it hit a ditch edge, somersaulted over a hedge and landed in a field. That was on a Triumph 2000. Second one was an Avenger - pretty much the same, but no hedge. I'm just lucky it didn't happen in town, as especially the T2000 wheel exhibited a surprising kinetic energy that would certainly have caused injury.

Reply to
Grimly Curmudgeon

So it didn't just "come loose". You believe somebody loosened it.

Reply to
Adrian

I had wondered about that, having seen similar vehicles since. But Fi racing cars have single centre nuts, and they come off frequently!!!!

Reply to
Graham J

Time for a bit of maths.

Take an average car wheel nut. 12mm thread, 19mm socket size. Weight approx

35g or 1/13th of a lb. Centre of mass at a radius of approx 8 mm. Tightening torque circa 70 ft lbs. Loosening torque is usually higher than tightening torque anyway but we'll ignore that.

That equates to a force of about 70 lbs x 12 x 25.4 / 8 = 2667 lbs if applied to where the centre of mass is or approx 2667 x 13 = 34671 times the mass of the nut. So it would require a wheel G force of a similar amount to undo the nut even if it were central to the wheel axis and a lot more given that it's offset from that centre.

So we're looking at forces thousands of times greater than the wheels can possibly accelerate or decelerate at to undo any type of fixing attached to them. It's therefore utterly inconsequential whether the fixings are l/h or r/h thread on any particular side of the vehicle.

Reply to
Dave Baker

Spoked wheels were generally centre lock with a left hand thread on the left wheel. Thanks for proving my point. ;-)

Reply to
Dave Plowman (News)

Right. A right hand wheel with right hand threads. Thanks for proving my point. ;-)

Reply to
Dave Plowman (News)

Did you read that bit, where I suspected dirty deeds?

Reply to
Grimly Curmudgeon

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