Wheel Center Bore Tabs + More difficult wheel balancing?

[Jlaa]

Hi gang, please see the backside of these wheels. These are OE Mercedes wheels - forged for Mercedes by Fuchs (you can see the Fuchs logo). These were original equipment on w220 S600s. These are hubcentric for MB 66.6mm hubs.

My question is this - why do these wheels have these tabs in the center bore? Why is the center bore not a full and consistent 360 degree circle?

My theory is that since tabs are not a full 360 degrees around the center bore, it makes for trickier balancing of wheel/tire assemblies --- meaning care must be used to have super LOW TAPER back cones on the balancer because a high angle high taper cone would cause the wheel to not exactly be centered on the balancer.

This uncentered hypothesis would be exacerbated if the wheel balance technician were NOT using a finger flange plate to press the wheel assembly onto the balancer via the wheel lug holes and just used the pedestrian rubber cup (that presses the wheel face) or the pedestrian center bore clamp (that presses the center bore hole of the wheel to the balancer). This is just my theory, and hence my ask about the tabs.

 

[Kira]

I do not know.
Perhaps a machined adapter is used instead of any tapered cone?

Do the edges of the circle formed by those 5 tabs match the 66.6mm hole (visible as the ridge in both photos)?
They appear to form a larger circle.

 

[Jlaa]

I do not know.
Perhaps a machined adapter is used instead of any tapered cone?

Do the edges of the circle formed by those 5 tabs match the 66.6mm hole (visible as the ridge in both photos)?
They appear to form a larger circle.

Thanks for reading. Indeed those wheels are OE MB Hubcentric and the circle formed by the edges of those 5 tabs are 66.6mm and the wheels fit tightly against the car’s hub. Just curious about the reasons for the tabs as I postulate their existence makes aftermarket balancing more fussy.

 

[The_Jeff]

So the tabs are there to center the wheel on whatever hub it's on. I postulate you'll get a better balance because they let the wheel fit more tightly, (tighter clearance and tolerances.)

The test is to mount this assembly on a wheel balancer, balance it, dismount it, rotate the cone an arbitrary amount, and remount. If the balance remains good, the system works.

 

[CapriRacer]

I've been trying to figure out why do this. And the best I can come up with is you can make the clearance between the wheel and the hub tighter (better centering) with less likelihood of the wheel sticking on the hub.

So as far as worse balance, I think the opposite would be true.

 

[Kira]

Do the 5 tabs also provide "corrosion breaks"?

Is a smear of anti-seize between hub and wheel a thing MB does?

 

[Jlaa]

So the tabs are there to center the wheel on whatever hub it's on. I postulate you'll get a better balance because they let the wheel fit more tightly, (tighter clearance and tolerances.)

The test is to mount this assembly on a wheel balancer, balance it, dismount it, rotate the cone an arbitrary amount, and remount. If the balance remains good, the system works.

I've been trying to figure out why do this. And the best I can come up with is you can make the clearance between the wheel and the hub tighter (better centering) with less likelihood of the wheel sticking on the hub.

So as far as worse balance, I think the opposite would be true.

Thanks guys. The reason I postulate that the tabs might make aftermarket balancing worse is because aftermarket wheel balancing machines) use cones that look like this:

That cone is tapered and allows the aftermarket wheel balancing machine operator to balance wheel/tire assemblies from multiple car brands without having an EXACT non-tapered cylinder mounted on the balancing machine for that EXACT car brand. For instance MB uses 66.6mm hubs. Audi uses 66.6mm and 57.1mm for some models. Honda uses 64.1mm. Chevrolet uses 78.1mm, 66.9mm, 70.3mm, and 67.1mm. Anyways aftermarket balancers use cones because its impossible to have *exact* hub sizes for every make.

I wonder if it is harder to truly center wheels with tabs in their center bores on high angle cones. This is in contrast to centering wheels on exact-sized-cylinders, which is what on-car-hubs are.

Just a thought, and hence my question about why some wheels are made with tabs in the center bores! Thanks for everyone's thoughts!

 

[Jlaa]

As a corollary, here is the car hub from a Porsche 911 of 1990s vintage. The car hub itself is not a continuous circle ---- the car's hub has three flanges .... and the wheel center bore itself is a continuous 360 degree circle.

Why does Porsche do this --- is it the same reason as above with the 5 tabs on the Mercedes wheel? Corrosion break? Easier centering of a hubcentric system? Just curious.

 

[The_Jeff]

Thanks guys. The reason I postulate that the tabs might make aftermarket balancing worse is because aftermarket wheel balancing machines) use cones that look like this:



I wonder if it is harder to truly center wheels with tabs in their center bores on high angle cones. This is in contrast to centering wheels on exact-sized-cylinders, which is what on-car-hubs are.

I don't know of any dealers that use anything but cones to center wheels for balancing. I'm aware of lug adapters but never seen them in the wild.

And the problem with cones is wear, and cheap tire dealers not replacing them when worn. They wear at the common diameters and get little "grooves" in them that interfere with a good fit. If you go to a MB only shop, then the cones will only wear in MB sizes!

It comes down to the care of the operator. Everyone seems to be in a race to the bottom buying and mounting "discount tires" with resultant disappointments.

 

[CapriRacer]

Thanks guys. The reason I postulate that the tabs might make aftermarket balancing worse is because aftermarket wheel balancing machines) use cones that look like this:

View attachment 316535

That cone is tapered and allows the aftermarket wheel balancing machine operator to balance wheel/tire assemblies from multiple car brands without having an EXACT non-tapered cylinder mounted on the balancing machine for that EXACT car brand. For instance MB uses 66.6mm hubs. Audi uses 66.6mm and 57.1mm for some models. Honda uses 64.1mm. Chevrolet uses 78.1mm, 66.9mm, 70.3mm, and 67.1mm. Anyways aftermarket balancers use cones because its impossible to have *exact* hub sizes for every make.

I wonder if it is harder to truly center wheels with tabs in their center bores on high angle cones. This is in contrast to centering wheels on exact-sized-cylinders, which is what on-car-hubs are.

Just a thought, and hence my question about why some wheels are made with tabs in the center bores! Thanks for everyone's thoughts!

The thing I always wondered about the cones was that the taper angle is different, so if the EDGE of the center hole of the wheel isn't straight and uniform, then the wheel wouldn't be properly centered. And the lug adapter doesn't fix this, BUT might help by applying different forces on each lug hole.

The way to tell would be to reindex that cone relative to the wheel and run the balance/Road Force function again. If you get the same result, the wheel is OK. If you get a different result, the wheel hub taper is buggered up. (How's that for a technical term??)

 

[Jlaa]

The thing I always wondered about the cones was that the taper angle is different, so if the EDGE of the center hole of the wheel isn't straight and uniform, then the wheel wouldn't be properly centered. And the lug adapter doesn't fix this, BUT might help by applying different forces on each lug hole.

The way to tell would be to reindex that cone relative to the wheel and run the balance/Road Force function again. If you get the same result, the wheel is OK. If you get a different result, the wheel hub taper is buggered up. (How's that for a technical term??)

Oh that's a great point! Thanks!

Using a cone on the back of the wheel/tire assembly on the balancing machine - this might engage the tapered part of the wheel center bore, so if the wheel center bore taper isn't 100% consistent and uniform around 360 degrees, then the wheel/tire assembly might not be centered on the balancing machine.

The challenge is that the manufacturer of the alloy wheel probably doesn't machine the taper of the wheel center bore with the expectation that the taper will need to be perfect --- they are probably more concerned about the flat part of the wheel center bore.

Hence using a shallow-angle collet (as opposed to a high angle cone) on the wheel balancing machine is a better bet!