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

evo77 (Automotive) (OP)
21 Apr 06 22:07
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 (Automotive)
21 Apr 06 22:28
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 (Mechanical)
22 Apr 06 8:05
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 (Automotive)
22 Apr 06 10:05

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

evo77 (Automotive) (OP)
22 Apr 06 11:02
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 (Automotive)
22 Apr 06 19:41
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 (Publican)
22 Apr 06 22:21
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
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

CapriRacer (Mechanical)
23 Apr 06 8:50
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 (Automotive) (OP)
23 Apr 06 13:41
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 (Automotive)
23 Apr 06 18:30
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 (Publican)
23 Apr 06 18:55
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 (Mechanical)
23 Apr 06 20:14
Tmoose (Mechanical)
24 Apr 06 8:27
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 (Automotive)
26 Apr 06 15:19

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 (Structural)
26 Apr 06 21:58
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 (Electrical)
11 May 06 20:37
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 (Automotive)
11 May 06 20:44
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 (Mechanical)
12 May 06 9:07
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 (Automotive)
12 May 06 10:39
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.
www.enkei.com

Mopar93 (Automotive)
17 May 06 18:50
> 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
 
Fabrico (Automotive)
17 May 06 19:23
"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)."

No one said the hole was not centered. With that in mind, does'nt it make sense to affix the wheel to a balance machine with 5 different quick-action cones so the machine can accomodate 1,000 different kinds of wheels and 30 different bolt patterns?

By the way, the big truck wheel balancing machines use studs only to mount the wheel.

CapriRacer (Mechanical)
17 May 06 20:41
"...With that in mind, does'nt it make sense to affix the wheel to a balance machine with 5 different quick-action cones so the machine can accomodate 1,000 different kinds of wheels and 30 different bolt patterns?..."

If I understand what you are saying - that 5 cones that would lines up with 5 bolt holes and that would be the only centering on the balance machine - then NO!!

First, there are 3, 4, 6, and 8 lug wheels so you'd need more adaptors.

Second, A mechanism to expand to all the bolt cicles used is really prone to misalignment - aggravating the centering problem.  I used one once and it was so difficult to use I tossed it.

Third, if the center hole is centering the wheel, then it only makes sense to use that.  I am aware that even with center hole piloting that an eccentric lug on the car can cause distortion, but that doesn't change the fact that the lug nuts are mostly for clamping - not centering.

NickE (Materials)
18 May 06 9:39
No, no, no, the cones are sized to accomodate the different center hole sizes. They dont fit the lug holes. Then you would need lots of combinations for passenger vehicles.

Fabrico -- I'm guessing that big truck wheels are more standardized with regards to bolt patterns. Correct?
Xwheelguy (Automotive)
18 May 06 10:17
I never said the hole wasn't centered either, Fabrico.  Just explaining the process of making a cast aluminum wheel in a mass production situation and why the pilot/hub hole should be and is used for centering passenger car and light truck wheels during balance and runout inspection.  The center of the bolt pattern has a tolerance in relation to the hub hole that is normally 0.3mm max.  If the lugs were used for balancing, then the center of the wheel COULD be off by that amount and possibly introduce inaccurate balance readings, whereas the pilot is closer to center and preferred to use for centering.

The only time that I've ever seen a wheel located by the lugs for any type of inspection other than torque checking is during runout inspection, checking the center of the lug hole pattern to the center of the wheel bead seats (where the tire seats) and the center of the lug hole pattern to the center of the pilot/hub hole.

Tim Flater
Senior Designer
Enkei America, Inc.
www.enkei.com

Fabrico (Automotive)
18 May 06 12:42

"No, no, no, the cones are sized to accommodate the different center hole sizes. They don’t fit the lug holes. Then you would need lots of combinations for passenger vehicles."

yes, yes, yes, that right, center hole used for convenience.

 "I'm guessing that big truck wheels are more standardized with regards to bolt patterns. Correct?"

Yes, and they only use half the lug holes to hold the wheel, ie: 5 studs for a 10 lug pattern, 3 for the old big 6 lug pattern.

spectreeng (Automotive)
10 Jul 06 18:56
Tim,

Even if the hub hole is the true center, and the lugs are off by a small amount - wouldn't you still want to balance it to the lugs, since installation dictates centering about the lugs, not the hub hole?  In otherwords, balance it the same way it would be installed and used.

Pilun
CapriRacer (Mechanical)
11 Jul 06 7:28
Pilun,

No.  If the hub is centering the rim, then the rim is centered on the hub (sic) and the lugs serve no purpose other than clamping.

In reality, though, even hub centric rims get a bit of distortion from off center lugs, but nevertheless, using the lugs to center for balance is only appropriate if the hub is NOT centering the rim.

Xwheelguy (Automotive)
11 Jul 06 10:48
Pilun,

I personally wouldn't.  Why take a measurement by anything other than the intended center?

Tim Flater
Senior Designer
Enkei America, Inc.
www.enkei.com

spectreeng (Automotive)
11 Jul 06 15:22
Tim,

If the subject was balancing OEM wheels, I'd say balance by the hub hole.  In cases where people are concerned about hub-centricity, such as the OP, it is because they have aftermarket wheels with over-bored hub holes - and are questioning the function of hub adapter rings (rightly so since there are plastic and aluminum variety).  Upon installing these wheels, even with hub adapter rings, it is the conical lugs acting upon the conical lug seats in the wheel that dictate the location of the wheel, not the hub.  To my understanding, the adapter rings only purpose is to _help_ installation by getting the wheel closer to center, making the installation of the lug nuts easier and less likely to scratch the wheel on the sides of the lug nuts.  Seems logical to balance these wheels that way, instead of by the hub hole which is for all purposes, floating around the hub.

Pilun
CapriRacer (Mechanical)
12 Jul 06 7:19
Pilun,

I think you'd be surprised about how much centering effect these simple plastic and aluminum hub rings have.

But there are a couple of other issues that you bring up:

The adaptor for using the lugs as centering for balancing  is a bit of a mechanical nightmare.  It's a fairly complex piece and IMHO adds more variation than it eliminates.

Besides, the only time centering is a real issue is when the bolt circles aren't centered.  So even if you use the rim lugs for centering, if the lugs on the vehicle are off center, the effort you put into the rim is for naught.
patprimmer (Publican)
12 Jul 06 7:43
This thread is starting to remind me of an old joke. It goes like this.

"Mummy mummy, why am I going in round and round in circles?"

"Shut up kid or I will nail your other foot to the floor."

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.

GregLocock (Automotive)
12 Jul 06 22:02
Probably not a bad idea to put this in context

A wheel and tyre assy weighs around 20 kg. A centreing error of 1 mm will give an imbalance of 20000 g mm

Typically you can detect out of balance of say 10g at 200mm radius, so 2000 g mm (probably not customer complaint level)

So, our centreing system needs to reproduce what is on the car to within 0.1 mm.

That's 4 thou, which is rough as guts as a clearance hole.

Cheers

Greg Locock

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

GregLocock (Automotive)
30 Jul 06 21:24
I've just found a drawing of a hub centric wheel. The centreing is done by a 6mm wide band, with a  dimension of 57mm+0.134+0.060, hole grade E9

I don't know what the mating part's dimensions are.

Cheers

Greg Locock

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

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