what part failed???
studs?
alloy hub??

What failed? got pics?

Studs failed, was a few years back now on an EF Falcon.

I was a supporter of them until my experience, i'm not saying i'm an expert on hub adaptors at all (as i'm not) but everything was done by the book.

i dont like the adaptors myself, but the studs failed, not the hub or its design... probably had cheap studs??

or the locating spigot in the centre was the wrong size, this is usually where failures occur.

I really don't understand why the $#%king things aren't made out of steel!! I'd dearly like to broaden my rear track and make the wheels look better in the arches by spacing out 25 or 30mm but I'm buggered if I'm gonna use alloy adapters!!

Stick an AU Diff in it, +36 - 42 mm each side depending on your rim offset (0mm or 6mm)

I don't think being made from alloy is a problem, they are billet alloy.. I would be more concerned about cast alloy rims failing before the hub adaptors..

Those style studs (press in with splines) are a BAD idea into alloy - period.

The original hubs are steel - steel is easy to machine and plentiful - the only reason i can reasonably see for hub adaptors being made of alloy is wank factor

I agree with the press in studs, I think if they were to fail that would be the week point..
the only reasons why I think they are alloy, is they are lighter and cheaper to produce..

otherwise, your right why not steel????

What's the issue with that type of press in stud? What's the alternative?

Aluminium is easily machined, and the right grade is more than strong enough for the purpose.

Press in studs cause spreading pressure in the material - combined with splines which form stress raisers there's very high risk of cracks forming (+ loosening) and you're using two very different hardness materials with also totally different heat expansion properties - which lends toward eventual loosening of the studs in place as well.

The CORRECT way to install studs in alloy would be thread inserts and screwed in studs - but that also brings in certain requirements as far as depth of threaded section - which would prolly make for adapters too thick for practical use.

I'd have no problem whatsoever using alloy SPACERS which sit over the studs and have centre hole properly sized to pick up on the hub centre spiggot - as long as the studs were then long enough to go thru the wheels and take nuts safely - but using adapters with press in studs leaves me cold.

Again, why not just use steel - would be super simple and mechanically sound - ie. exactly same basic form as the hubs themselves.

Considering the only failures I've seen/heard of are the studs failing. I have no concern for the adapter failing due to the 'pressing' of the stud.

Press fits in aluminium are used in many places, this is not new territory.
The cuts made by the splines may indeed be stress concentrations, but if there is little stress generated in that direction, there will be little stress to concentrate.
Thermal expansion may cause an issue if you try to undo the wheel nuts while the adapter is at an elevated temperature, as the press fit will become looser, but I see no way that it will cause the nuts to come loose any more so than using an alloy wheel on a steel rotor.

From my industry, screw in lifting points need to be engaged in material that is 2x thread diameter thick to meet their rated working load limit in aluminium alloys, and 2.5x in aluminium-magnesium alloys.
So a Ford stud of 1/2" would need to be threaded in to 1"(25.4mm) of aluminium alloy or 1.25"(31.75mm) of alum/mag alloy.
Those dims work perfectly for the most common application here. (36mm adapaters.)

These type of lifting points are rated to fail at a minimum of 4x their rated WLL.
Eg: An M12 lift point will work up to 4x 750kg (3000kg) before failing, no matter the material it is screwed in to as long as it meets the requirements.

The biggest issue with hub adaptors is 99% of cheap adaptors run an M12x1.5 thread. People buy them and use 1/2 inch wheel nuts. You don't have to be a genius to figure out that the thread difference loads the studs alot more, causing stripped threads, and snapped studs.

I will never put alloy adapters with pressed in studs on my car - I do not consider it to be safe.

In the hub adapter application, even with screw in studs that meet specs for tensile loads, I'd still be wary considering the potential shear loads also involved (I think there'd be a reasonable chance of the studs loosening) - but provided they were properly/well made I could live with them (would be checking tension regularly). I'm personally after 25mm adapters so 25.4 would be near enough.

I would have no issue using steel adapters with pressed in studs.