19 replies to this topic

[cradley-heathen]

today i had to take a wheel off a customers car which had a set of those blue coloured wheel nuts on. i had always assumed they were just steel nuts with some kind of paint or other coating, i didnt realise they are actually anodised aluminium ones!

being quite into weight saving (and they were really very light!) i may be tempted to get some for my car, but based on 2 things......

1, are they actually any good/safe? i would imagine they would be very easy to strip the threads?

2, can you get them in plain silver or black? as i kind feel they look a bit naff in red or blue.

[Cooperman]

You would need to know that the alloy nuts were from top grade alloy. Fatigue is always a potential issue with aluminium alloy nuts and they should not be used in high-load or high potential fatigue applications unless full stress analysis has been carried out.
Porsche use alloy nuts on the 911, but one might imagine that a full analysis has been carried out. They do cost a fortune as well.
Think I'll stick with steel just to be safe.

[cradley-heathen]

this is my concern Cooperman! im sure alloy nuts can be safe, just maybe not these ones?

[tiger99]

They are completely unsafe, and therefore certainly illegal, like any other vital part of a car which is not fit for purpose. The law does not need to prohibit, or even mention, them specifically.

In any proper combination of nut and bolt,it is vital that the materials are matched such that the bolt always snaps first if overtightened, to give a very visible warning. With any grade of alloy, that rule is violated, and they may be tightened up to the point where the threads are beginning to strip without there being any visible warning. That is clearly unsafe.

The best grade of alloy imaginable will be at the point of stripping when torqued up correctly.

It is unfortunate that there seems to be no control whatsoever on what dangerous products may be sold, and it is the end user who will carry the can, when the inevitable accident happens.

[Shifty]

Sounds like "too much pain for too little gain"

[Cooperman]

If slightly longer studs were used and absolutely top-grade aircraft quality aluminium alloy used to make a deeper thread engagement that should work. However, the weight saved would be minimal and would not be worth the cost of the special manufacturing.
If you are Porsche, then cost is not an issue and my old '73 Carrera had alloy nuts. They had a lot of engagement though.

Edited by Cooperman, 20 April 2012 - 10:55 PM.

[cradley-heathen]

im glad its not just me that thought they sounded dodgy.

i cant believe i havnt heard horror stories about these? as i said earlier, i have seen them for sale at shows etc, but never looked at them as i assumed they were just steel ones that had been coated or painted. it was only when removing them today that i realised they were actually aluminium as they were super light.

i think i'll give them a miss!

[Sam Walters]

If you have access to a lathe and you can find some 0.75"/19mm 7075 hex bar then its worthwhile. Elsewise its not.

[Cooperman]

If you have access to a lathe and you can find some 0.75"/19mm 7075 hex bar then its worthwhile. Elsewise its not.

And the fatigue analysis shows what in terms of required thread engagement length and life-cycle?

[Ethel]

Sure they weren't titanium?

[tiger99]

Titanium would not help. Weight for weight it is stronger than steel, but based on physical cross section and shear loading on the thread it is not, so the threads would still be too weak. Remember that it is grade 8 steel which it has to equal.

There is a fundamental difficulty because due to bolts stretching and nuts compressing under load, the load is carried on the first two or three threads. With lower grades of steel, you could rely on plastic deformation to spread the load a bit more, but with any light alloy, ibcluding titanium. that will take you well into the fatigue region. The first time they are torqued up, they "may" work (not guaranteed), the second time the threads are likely to shear due to fatigue loading, without warning

You can actually use titanium nuts on titanium bolts, but not titanium on steel. Always, the strength and stiffness of the nut must be correctly matched to the bolt.

An odd combination of materials needs comprehensive analysys backed up by proper fatigue life testing, to ensure it is safe, and you can be absolutely certain that it has not been done, as it would be disproportionately expensive.

[Glenn S]

Tiger 99 for info if we go back a few years, (Cooper man will remember) you will find Triumph fitted Alloy wheels nuts to the 5 spoke 14" Alloys fitted to Stags and 2500S saloons also these same wheels with alloys nuts were used on MGB GT v8.

[Pete649]

I don't mean to hijack this thread but the Zcars front tubular subframe uses aluminium tie rods with spherical rod ends. So the threads between the rod ends and the tie rod will not be matched. The drop links are also aluminium. I was not happy with those and had some steel ones made up but I still a little concerned with the tie rods. Delving on the web shows that as a rule of thumb the minimum thread engagement for steel into aluminium should be 3 to 1. I could always measure how much thread engagement I have and if it is not adequate have some steel tie rods made up. Anyone have any comments on this?

[Cooperman]

It's interesting and maybe significant that in aerospace any highly loaded thread into aluminium alloy has to be fitted with an approved Heli-Coil to prevent thread friction causing thread failure in the alloy.

I do remember some manufacturers fitting alloy wheel nuts, indeed my old '73 Porsche 911 Carrera had them, but they were a very high grade alloy and there was a lot of thread engagement. They seemed to work OK, but no doubt Porsche did the stress and fatigue analysis very thoroughly.

For a Mini I'll stick with steel nuts.

[kcchan]

I've been doing a little research into wheels for my project and what springs to mind is that the weight you are trying to save is very close to the centre of the wheel and in terms of inertia, you'd be better off using lighter tyres (if they exist).