Explain this! Cos I can't.

[Pondy]

My 'Fauxrrari' has wire wheels which are held on (!) by knock on spinners. There are hub adapters (as per the photo) which bolt to the Z3 hubs. These have a huge thread which the spinner screws onto. The threads are handed on opposite sides of the car, so the theory is that they can only tighten not loosen when driving.

Well...my wheels have constantly been coming loose after a few miles of driving. I was initially using the traditional method of whacking the ears of the spinners with a big white rubber mallet. This wasn't tightening them enough. So....I used a spinner tool which came with the wheels. This is a big aluminium lump which sits over the three ears of the spinner, with a 38mm socket on. This was connected to a socket handle and a 6ft pry bar on the end of that.
Hanging on the end of the pry bar I got the spinners to tighten more. Happy days!
Nope. The wheels would take longer to loosen than before but still were coming loose. I had run out of ideas.

I called a company who I know supply the type of wheels I have (they didn't supply mine though). I was told to use grease! Grease.....on the outside taper of the spinner and the spinner threads, then just use a rubber mallet.

I was confused. How can using grease (which is meant to help slippage) stop my spinners from loosening? "Just try it" was the answer.

It has worked a treat. I can tighten the spinners more with a rubber mallet than I could with a 6ft bar and they don't come loose!!

I still don't understand why, though. I thought I knew a bit about physics but this has completely baffled me. I have never ever greased or lubricated mating surfaces before.

 

[Wildfire]

No idea, but on the hub of my motorbike I was told "do not grease it up or it won't come undone later on." So maybe the same thing?

 

[axelleveau]

When you apply grease you reduce the friction in the threads. This allows you to do more turns, hence have more stretch, for the same tightening torque. You might think: "so what? It will be just as easy to take off with less friction!" BUT the cool thing is that the additional stretch will hold pressure more consistently when vibrating, also the friction against the wheel will be greater and this still does not have grease so that will hold better with more stretch.

 

[Matt.rowley.1990]

When you apply grease you reduce the friction in the threads. This allows you to do more turns, hence have more stretch, for the same tightening torque. You might think: "so what? It will be just as easy to take off with less friction!" BUT the cool thing is that the additional stretch will hold pressure more consistently when vibrating, also the friction against the wheel will be greater and this still does not have grease so that will hold better with more stretch.

And you probably reach a point where the increase in clamping force overcomes the frictional losses achieved through greasing of the threads.

 

[mmm-five]

If they're handed are they fitted to the correct side of the car, so that they are tightening when being driven

 

[ARCS]

If they're handed are they fitted to the correct side of the car, so that they are tightening when being driven

This is what i was just thinking.

 

[Pondy]

If they're handed are they fitted to the correct side of the car, so that they are tightening when being driven

The same should be the case whether greased or not, surely?

This is another thing I don't understand. I could understand it if they were tightening so much I couldn't get them off, but the opposite was happening.

 

[Pondy]

And you probably reach a point where the increase in clamping force overcomes the frictional losses achieved through greasing of the threads.

Again, something I don't understand. Grease will create a thin 'barrier' between the mating surfaces, thus there is no real friction or clamping force. As grease is essentially a liquid, if it has nowhere to go it will hydraulic which should push the two surfaces further apart. At least that's how I see it. But I am obviously wrong, as that isn't happening.

 

[Pondy]

When you apply grease you reduce the friction in the threads. This allows you to do more turns, hence have more stretch, for the same tightening torque. You might think: "so what? It will be just as easy to take off with less friction!" BUT the cool thing is that the additional stretch will hold pressure more consistently when vibrating, also the friction against the wheel will be greater and this still does not have grease so that will hold better with more stretch.

That is a great answer, thanks!

 

[buzyg]

The Grease is reducing vibration and allowing the handed set up to do it's job better. As someone else said it's down to torque on the spinners.

 

[MikeyH]

Many years ago my MGB had wire wheels and I would hammer them on with a mallet from an old Blackburn that the nice old guy up the road gave me. I don't ever remember them coming lose or having grease on them, was a long time ago though. I did hammer both wings each time until they were good and tight. Mike.

 

[Pondy]

Many years ago my MGB had wire wheels and I would hammer them on with a mallet from an old Blackburn that the nice old guy up the road gave me. I don't ever remember them coming lose or having grease on them, was a long time ago though. I did hammer both wings each time until they were good and tight. Mike.

Your spinners and wheels were probably not made in an obscure Chinese factory, though, Mikey where quality control is not something they think about too much.
Yours were probably made on a lathe in Abingdon by a bloke called Malcolm who was very good at his job. I would also guess the spinners were made alongside the wheels, so they were matching items.