Lug nut / wheel 'seat' taper design?

[Bob S.]

Hello -

Are there any automotive engineers here who are intimately familiar with the design of lug nuts and the mating tapered 'seat' in the wheel? I'm wondering if the included angles are identical in the wheel and on the nut.....or if the included angle on the nut is slightly greater to cause the contact between the nut and wheel to occur at the outside of the taper? I'm actually considering the case of a cast aluminum wheel and steel nut.

If there is a difference, my next question would be how much?

(As a retired auto engineer myself, I'm aware of other heavily loaded tapered connections where such a difference in included angles is employed to control the location of contact.....)

Thanks for any insight you can provide!

Regards,
Bob S.

[Chuck S.]

Re: Lug nut / wheel 'seat' taper design?

I'm not an automotive engineer, but as a retired mechanical engineer, I can tell you there is absolutely no logic in deliberately making the angle of the seat and the conical lug nut different. The angles are likely the same, or very close, say within minutes of a degree.

Making the angles the same accomplishes the objective of precisely centering the wheel on the studs with zero possibility for movement, while maximizing the contact area to reduce point loading. Point loads would be an important consideration in making the wheels as light, and as strong, as possible.

In all the times I've changed my alloy wheels with tapered seats and conical lug nuts, I've never noticed any evidence of point contact; i.e. a "ring of wear", as from using two different angles for the lug nut and the seat. Such a wear pattern would eventually, IMO, compromise the intended purpose of the conical seat by preventing good uniform torqueing. In my experience, the steel lug nuts are smooth polished chrome with complete contact in the conical seat, thereby creating little opportunity for deep wear patterns.

[Michael H.]

Re: Lug nut / wheel 'seat' taper design?

Hello -

Are there any automotive engineers here who are intimately familiar with the design of lug nuts and the mating tapered 'seat' in the wheel? I'm wondering if the included angles are identical in the wheel and on the nut.....or if the included angle on the nut is slightly greater to cause the contact between the nut and wheel to occur at the outside of the taper? I'm actually considering the case of a cast aluminum wheel and steel nut.

If there is a difference, my next question would be how much?

(As a retired auto engineer myself, I'm aware of other heavily loaded tapered connections where such a difference in included angles is employed to control the location of contact.....)

Thanks for any insight you can provide!

Regards,
Bob S.

Not sure what the angle of the nut seat is/was on original wheels but the original print for the nut called for an included angle of 59*
On 4 Oct 1979, the print was revised and the angle changed to 62* +/- 1*. The part number remained the same.
I suspect there may have always been some slight intentional difference between the nut seat in the wheel and the nut. The wheel flexes slightly when the nut reaches proper torque.