Do I need hubcentric rings for my 15" Konig Heliums on my 94 hatch? I haven't been using them because I never thought of it being an issue but is it. Atually, what is the purpose of these rings?

 

It puts the weight on the car on the hub instead of the lugs. You should have them.

 

Really, if you bolt them up carefully, tighten the lugs progressively, and torque to the correct specification, the hubcentric rings are not a big issue.

If you got the same plastic ones that I did with the Konig Reigns for my wife's CRV, think about it like this - you could pinch one of them in a pair of pliers and deform it. How much pressure could it actually stand? The math is complex but the squeeze of the lugs on the surface of the hub makes for a huge load carrying capability.

My theory is to not sweat them but do what makes you most comfortable.

Kirk

 

I agree with Kirk. The clamping load & surface friction should be fine to keep them in place. You do have to make sure that the lugs are at least snug before lowering the tire/wheel down.

The latest issue of GRM actually addresses this ?. The Tirerack column talks about it. He is saying that they should be used. @ my friend's shop, there have been a couple of cars they really needed them. Otherwise, the tire/wheels would do weird things (oscillations sp?).

Hmm. I just contradicted myself. OK. In most cases, I don't think it is really an issue. If you do end up using them, make sure to go with some al ones. The plastic ones can melt when used on the track.


[Modified by civicrr, 8:37 PM 9/13/2002]

 

It's true that the clamping force of the lug nuts is WAY more than necessary to keep the wheel in place. Some calculations from an engineer I could dig up if I *really* wanted to, done to approximate the picture with the NSX, being 5 lugs @ 75ft-lbs with a steel hub and aluminum wheel (different metals have different coefficients of friction), approximated that it'd take something like 30,000lbs of force to break the friction between the wheel and the hub. That basically means the wheel and the suspension will get damaged before the wheel moves against the hub.

Also note that when the car is cornering, the forces you're looking at most are not vertical loads, but lateral loads. The lateral loads are applied longitudinally along the axis of the lugs.

What you *do* need to be careful of, though, is that if you don't tighten the lugs evenly a little bit at a time (for example, you reef down on one lug nut before tightening the others), the wheel will not be properly centered. Just go finger tight on all the lugs, to make sure the lug nut seats pull the wheel correctly into position before you tighten them down. Also, I get them as tight as I can while the car is still in the air before I put the car down. I don't have any solid theory behind that, it just seems like a good idea to me, since it doesn't really require any extra effort.

-Mike

 

I was curious to see if my memory was correct, so I looked up the emails. Here's some random stuff.

>But when you think about it, it doesn't make sense that a
>hard plastic ring that can be popped in and out by hand
>would have any significant effect on the load bearing
>capabilities of the wheel/hub interface.

It doesn't. It simply aligns the wheel to the hub more precisely than the
studs can. Then, once the lugs are tightened down, the friction between the
wheel and the hub mating faces is what really carries the load. That's why
you have to torque lug nuts so tightly- so the friction force is high.

This way, studs see mostly tension forces from torquing them down (and
cornering), and the friction carries most of the bump and drive/brake torque
load.

Example- (5) 7/16"-14 (.438") studs torqued to 75ft-lbs exert a total
preload of 44,362lbs(!!). If the friction coefficient between the wheel and
hub is 0.45 (steel-aluminum), then it will take a 20,000lb vertical load to
overcome the frictional force enough to budge the wheel even slightly. Only
then will the hubcentric ring and the shear strength of the studs come into
effect. Considering the static loading on a rear wheel of your NSX is about
900lbs, that would be a 22g impact- and by that point you have bent rims

-------
and some more after I asked how he arrived at those numbers
-------

Hehe... OK, here's where I got my info:

Coefficient of Friction, steel on aluminum, static (0.45): Machinery's
Handbook, 25th Edition (Industrial Press, Inc) p. 189
(note- p. 190, aluminum-aluminum, can vary from 0.30 to 1.30)

Fastener torque/preload values: I pulled them from a handy reference
slide-rule chart. Holo-Krome Company, Lancaster PA, "Socket Screw
Selector". I looked up a 7/16"-14 fastener (WAG- seemed about the same size
as most studs I've dealt with) and then saw that if torqued to the
recommended torque (1,190in-lbs = 100ft-lbs), each would give a preload of
11,830lbs. Scale that preload torque down to 75ft-lbs (common automotive
torque value for lug nuts), and each gives a preload of 8,873lbs. Multiply
by 5 (NSX), and you get 44,360lbs preload. Multiply the preload times the
coefficient of friction to get the total static friction "holding" force.

By the way, these studs would have a minimum tensile strength of 19,100lbs
each- or 95,500lbs for the wheel. That's static; fatigue usually sets in
and they will crack at a lower load eventually.

This is everyday steel- good stuff, eh?

Charts are good and simple. Easier than looking up the formula for preload
as a function of diameter, pitch, stiffness of material, joint stiffness,
lubrication, etc.