Hub-centric wheels question

[BenzBoy]

I've noticed that lately on RR there's been a fair bit of talk about using hub-centric rings when mounting wheels.

To me this seems to be a recent thing, and I can't think of any wheels I've swapped on any of my cars sitting bang-on over the hubs (including OEM wheels) - I've always trusted the wheel nuts to make the wheels hub-centric as they are tightened, as the conical or convex seats pull things central.

Have I been dicing with death all these years without realising? Are hub-centric rings along with regular wheel bolt seats more a "belt and braces" approach? Are certain wheels in need of hub-centric rings by design?

I don't really understand why they're needed if you have regular taper seat nuts or bolts?

[Blown_Imp]

Hubcentric wheels are for preventing wheel wobble, that is all (I am prepared for the flaming that will ensue).

The bolts that secure the wheel do so via surface friction, and the safety factors involved are huge.

If maths is required I can provide

[ChasR]

It depends on the wheels TBH. On the larger profile stuff you may not really notice. MGBs for instance never located on the hubs and were fine. Triumph Stags located on the wheel studs instead of the wheels and as a result they can cause seemingly incurable vibrations (most alloys on them were never drilled centrally from the factory. FWIW Stock Stag wheels used sleeved nuts to locate the wheel on.

There is a thinking IIRC that the hub itself holds the wheel on to a degree. IMO modern stuff works better with the wheels being located centrally, but that seems to be more down to the wheels themselves (low profiles etc.).

[cobblers]

Again, to echo what other people have said and something I've had to explain to loads of people over the years (who still won't believe me)

Spigot location along with taper/radius bolts are only used to stop idiots getting the wheel on slightly off center when they put one bolt in, torque it all the way up and only then bother with the others. In an extreme case this could cause a false torque on the wheel fasteners ending up with wheel wobble and eventually losing a wheel, but you'd really have to try very hard to get it this wrong.

Any normal person who just puts the bolts in hand tight first will locate the wheel perfectly well enough, spigot location just makes this a bit easier.

There is absolutely zero load on the central hub - if there was any, it would mean that the wheel was moving on the hub face and there was an axial load on your bolts, which would cause them to loosen or snap off pretty quickly.

IIRC each bolt when torqued down provides something in the region of 10-20 tonnes of force clamping the wheel against the hub.

[RobinJI]

What Blown_Imp says, they're nothing to do with holding the wheels on as such, so the way I understand it, there's no real danger to not having them a tight fit, they just to centralise things while the bolts are done up. If you're smart about doing the bolts up, and the bolts are capable of locating the wheel themselves, then there should be no need for them.

The issues arise if you use bolts that wont locate the wheel, like wobble bolts, or if you drop the cars weight onto the wheel with the bolts still completely loose. Having both bolts that locate the wheel, and a correctly sized spigot just idiot proofs things a little more.

Personally if the car has bolts I like having the wheels as a tight fit on the spigot, just because it makes life easier when putting them on, but on a car with studs it makes no real difference to me, as I always nip the nuts up a touch before dropping the cars weight onto the wheel anyway. I've got no concerns about running wheels with incorrectly sized spigots, I have done trouble free in the past, and plenty of cars haven't used them from the factory without issue, it's just a convenience/fool proofing thing.


Edit, if they were there to provide any structural role, then they wouldn't be able to be the loose fit they are even when 'correct', they'd have to be an interference fit to prevent the wheel shifting around and wearing the mounting faces/fatiguing the bolts.

[BenzBoy]

Thanks for the detailed responses. So it's pretty much as I thought then, nothing to worry about!

The only time I've encountered any extra measures to locate a wheel was a metal peg sticking out of the hub on a Saab 900 (I think it was on my Saab anyway...)

[Blown_Imp]

Bang on Robin, any movement around the central hub would cause surface fretting and wear within a few miles if it was not an interference fit.

In the words of Colin Chapman, you can hang a double decker bus off a 1/4" bolt (6mm), this is truth. Imagine what an M12 bolt can take? Then put four or five of them on a wheel, yeah, that strong

J

[ChasR]

The Alfa 147 I drive now and again also has that on the wheels. Considering they have wheel bolts to put the wheels on with, locating the bolts is a doddle!

[DWDarkWheels]

Interesting discussion. I've always preferred the belt and braces approach. Having said that, the Scimitar has zero centralisation at the back as standard (and on sleeved nuts). Robin makes a good point about hub-centric spacers needing to be interference fit to really work.