What is the relation between a hub centric wheel and the hub?

[evo77]

A debate on another car forum is going on in regards to what defines a hub centric wheel. We know that most if not all vehicles today have the center bores of their wheels machined precisely to the diameter of the hub however its unclear as to whether or not the purpose of a hub centric wheel is merely to center the wheel for balancing purposes or to actually relieve stress from the studs and bear the weight of the vehicle or to do both.

Some feel that the wheels do not bear load and that the studs are the ones taking the grunt of it all.

 

[GregLocock]

The studs provide the clamping force, the friction reacts the loads. The hub is there for centreing only. It may react some exceptional (kerb strike) forces.

If it reacted the normal loads then you would see fretting, since it is a clearance fit.



Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[CapriRacer]

I agree with Greg with this one exception: Cornering forces will load and unload the clamping mechanism.

On a related note: Is the center bore of a hubcentric wheel tapered? How much? What about the hub? Is it an interference fit?

I know, I know! It's going to depend on the manufacturer - wheel and vehicle. But is there any commonality?

Thanks in advance.

 

[Fabrico]

In general, cars wheels are centered by the lugs, truck wheels pilot on the hub. Hub pilots are not tapered.

 

[evo77]

So is the consensus so far that a hub centric wheel does not rest on the hub bearing weight of the vehicle?

This is what Ronal Wheels USA had to say about hub centricity...

"Hubcentric" is another term that is often not mentioned or is misunderstood. A hubcentric wheel is a wheel designed with a centerbore opening to match the exact diameter of the hub of a specific vehicle. The importance is that the weight bearing of the wheel, in reference to the vehicle, is accomplished by the hub and centerbore mating to an exact fit. The lug nuts/bolts' only purpose is to affix the wheel to the mounting surface, not to bear the weight of the vehicle. Often wheels that are not hubcentric create driveability problems--shimmy, vibration, and erratic tracking. Many quality manufacturers design their wheels to be versatile by providing hubcentric centering rings that snap into place inside the wheel, to make the wheel hubcentric. This is an important safety issue--hubcentricity is highly recommended.

 

[GregLocock]

Shrugs. That is not an engineering document - what is an 'exact' fit?

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[patprimmer]

My aftermarket aluminium wheels have a replaceable plastic adaptor to adapt the wheel to various hub diameters. I doubt a piece of Polypropylene can bear much weight, and therefore does little more than centre the wheel until the wheel nuts are tightened.

The nuts and the mounting holes are tapered seat, so they will create a considerable force to centralise the mounting holes in wheel over the stud as the nut is tightened.

Regards

eng-tips, by professional engineers for professional engineers
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[CapriRacer]

evo77,

You have to be careful about what info is posted on a web site - even a company web site. Personal experience says that this is mostly a sales and marketing function and can't be relied on for accurate technical info.

Fabrico,

I think you are 100% wrong about cars generally not being hubcentric. My experience this that nearly 100% of the OE wheels are hub piloted, and, if anything, the truck wheels lagged behind, but they also are nearly 100%. In fact I can't think of any vehicle manufacturer that doesn't use hubcentric piloting. It's only aftermarket wheels that aren't and that's because the hubs are not standardized. In order to have hub piloting, aftermarket wheel manufacturer are using hub rings to center the wheel.

So I still don't have an answer I can trust about taper, etc.

 

[evo77]

See the thing is, I haven't found anything that disproves that the hub supports the weight. Most articles from car magazines, wheel manufacturers and even repuatable tire/wheel sources such as tirerack even state that the lugs only serve a purpose to affix the wheel to hub while the hub bears the load.

 

[GregLocock]

If the weight were taken by the spigot on the hub, rather than by friction at the wheel / hub interface) then there would be sliding wear on the flange of the hub, and rotational wear marks on the spigot.







Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[patprimmer]

Old VW Beetles did not have a central spigot to locate the wheel on the hub. They therefore cannot be hub centric.

They were extensively used in off road racing and as the basis of buggies because of the durability of their suspension and drive train under severe conditions and brutal manner of operation.

They were not prone to wheel hub interface failure.

How much more proof do you need.

The matching tapers on the wheel nuts and wheel mounting holes and the mounting face of the hub must firmly hold the wheel in all directions.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Tmoose]

Non hub centered passenger cars.
Original VW beetle, Renault 16, Peugeot 404, 1978 HOndfa Accord.

http://www.bfyobsoleteparts.com/volkswagen/files/master/thumbs/t_11828.jpg

http://edge-op.org/images/4CV/300/dsc00105.jpg

http://www.grapa.net/peugeot404/images/404dieselw10d100j3.jpg

 

[Tmoose]

A 7/16 bolt torqued to 50 lb-ft exerts about 7000 lbs of clamp force. A wheel using 5 of them, with wheel-to-hub interface friction coeffecient of just 0.1 should not slip until asked to support 3500 lbs or so. Once again, friction is my friend.

 

[Fabrico]

Judging by the lack of hub protrusion on vehicles of all sizes, and the loose fit on many that do have them, it is not unreasonable to conclude that with a tapered lug system, the protrusion does nothing beyond easing installation of the wheel.

 

[NormPeterson]

Like Pat, I have a set of aftermarket aluminum wheels (for the Street Touring autocross competition tires) that have plastic centering rings. They only seem to assist in getting the wheel on more accurately such that torquing down the lug nuts does not have to move the wheel radially to any great extent. Saves wear and tear on the wheels' lug stud hole taper surfaces.

Further, since this particular car is a '95 model and has lived outdoors essentially all of its life, the hub protrusions had corroded a little, such that the OE wheels required some physical (and verbal) persuasion to get them off, after which time they grabbed the centering rings out of the aftermarket wheels upon their removal. So a tiny bit of clearance is necessary for anything resembling normal maintenance/tire rotation/tire replacement. I take that to mean that the term "hubcentric" cannot mean that the hub protrusions carry the wheel loads as a normal condition, only that the wheel is more closely centered during the initial stages of installation than if you have to hang it off a lug stud.

Norm

 

[marcdeluca]

Does anyone remember the old Cragar mags? They were truly hubcentric; the lug holes were slots so they could fit various bolt circles, and the lugnuts were flat faced and used flat washers under them. I believe that any wheels that have a lugnut with a bevel against the wheel is a lugcentric wheel. Alot of tire shops have trouble balancing aftermarket cast aluminum wheels because the wheel balancer clamps to the hole in the wheel instead of the lugs. The hole isn't necessarily in the center on a casting. So, the best way to balance is to use a lug adapter on the balancer, with which you actually bolt the wheel to the balancer with studs and nuts like on the car. The trouble is that most shops don't want to spend the extra time it takes to do all that.

 

[GregLocock]

Or you find a place with an on-car balancer. You don't see those around so much, did health and safety kill them off?

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[notnats]

I had several Peugeots, 203, 403 and 404. They all had 3 stud wheels locating on conical seats under the nuts. In addition, the wheel had no hole in the centre, which made it really difficult getting someone to do a wheel balance. Nobody wanted to fit the appropriate adaptors to their balancing machine.

 

[Xwheelguy]

Greg,

Have you seen the Hunter balance machines? They check the wheel, with or without the tire mounted, as if it were in mounted vehicle position but not held onto the balance machine by the lugs...they use the standard balance cones to keep the wheel centered properly. They can also check runout of the wheel at the same time (although not dead nuts accurate).

marcdeluca,

I assume the reason why wheels aren't balanced by their lugs is because most wheels are machined/lathed with the hub being the point of centering in the lathe (lugs usually aren't drilled until AFTER wheels are lathed so that the wheel will locate from a machined hub hole versus a cast hole, which has more slop), so the wheel is more than likely going to retain its center closer to the hub than it will the lug holes. However, tight runout and bolt circle to pilot tolerances usually make up for the differences or slop introduced when the lugs are drilled, which would more than likely add to inaccuracy during balancing.

Not only that, but I would think that clamping down the entire mounting surface would lead to innaccurate balance readings compared to something that was smaller in diameter than the mounting surface but still located as near to center as possible, like the hub/pilot hole. Hope that makes sense.

Tim Flater
Senior Designer
Enkei America, Inc.

http://www.enkei.com

 

[Mopar93]

> I haven't found anything that disproves that the hub
> supports the weight. Most articles from car magazines,
> wheel manufacturers and even repuatable tire/wheel
> sources such as tirerack even state that the lugs
> only serve a purpose to affix the wheel to hub while
> the hub bears the load.

It is true that the hub is bearing the load, but not at the machined center where it protrudes into the wheel. There is no way that portion of the hub could bear the load unless there was zero clearance between the hub and the wheel.

The hub is bearing the load, not at its center protrusion, but rather at the wheel bearing locations.

Similar to what others have stated, once the wheel is "clamped" to the hub, the hub and wheel become one assembly. This is no different than a two-piece wheel being bolted together. The load isn't taken at the bolts clamping the two halves together as the wheel is essentially one unit at this point.

In most cases, the protrusion of the hub is there because the design requires a wheel bearing in this area of the hub. If the wheel bearing wasn't there, the hub protrusion wouldn't be required. In that case, there would also be no need for a hole in the center of the wheel.

-Maurice