Hub centric vs lug centric rear axles

[Skip Fix]

Most factory rear axles(and front hubs) have the pilot diameter tight in the wheel and it sticks out enough to locate the wheel. I assume it gives some stability there especially with side loads.

Many aftermarket axles have a much shorter pilot, barely sticking out past a brake drum/disc hat. The axle manufacturers say the studs do all the work. I would think the factoery wouldn't have kept such tight tolerances if it didn't help some. Although many aftermarket wheels are not tight on the pilot.

What do you engineering guys think, and issue for custom axles with a longer pilot or the off the shlef ones?

[Tiger]

It should be easier to get a more precise centering of the wheel if its centered on the pilot compared to centering it on the studs, thats my opinion at least.

[Skip Fix]

Mine also, as even lugnuts for aluminum wheelas have some free play.

[Blown353]

The hub register is only there to get the wheel close to centered prior to tightening the lugnuts. All the loads of the wheel are carried via the clamp load and friction between the wheel and the hub once you tighten the lugs. The only time the wheel to hub fit will be a load path is in the event of a shock load strong enough to overcome the friction between the hub & the wheel... and that's a LOT of force!

Hubcentric is nice because it gets the wheel concentric to the axle prior to running the lugs down. The lugs *should* center the wheel on their own, especially if they're conical or ball seat. However in rare cases if you haphazardly mount a lugcentric wheel there's a chance of getting the wheel off-center and causing a very noticeable vibration from the runout. I've seen that before when a tire-monkey runs the lugs down with an impact without any crisscross pattern or tightens the first lug to full torque prior to running the others down snug.

I'm an engineer by trade and I know about the lugs centering the wheel and the friction doing the actual holding of the wheel, and never had a problem with runout on my previous wheels which were lugcentric. I mounted them all using hand tools, snugging first in a criss cross pattern, then torquing down criss-cross in 4 increments. But if it says anything I custom machined some rings to make my new wheels hubcentric. So, I vote for getting the axles with a longer pilot if the cost isn't too exhorbitant.


Just for some info, here's what I did with my new wheels. Inside of wheels as shipped. Oversize centerbore, not hubcentric...



After some quality time with a lathe and some 6061-T6 barstock (plus Alodine conversion coating afterwards for some corrosion protection) we have 4 of these. Sized to be .0015-.002" press fit into the wheels and .004-.006 total clearance over the front hubs and rear axles. The adapters sit .015" below the wheel's mounting pad.



The finished product. Put a light smear of loctite on the adapter rings prior to tapping them in for good measure.



And that's how you make a lugcentric wheel hubcentric.

[nancejd]

Cool idea, how do you verify that the center hole is actually centered in the rim?

[Blown353]

Cool idea, how do you verify that the center hole is actually centered in the rim?

I chucked the wheel up on a large lathe and checked the hoop to centerbore concentricity with a dial test indicator. I would have used our big CMM but it was busy doing "real work." The actual machining flow may vary by manufacturer, but in my mind the most logical flow to machine the OD of the wheel center section so it fits into the hoop section and also to machine the bolt pattern the centerbore would probably be the first operation and thus everything should be concentric to the centerbore.

[MonzaRacer]

Hey its comon sense as ost one piece wheels are machined by lathe so the center hole HAS to be concentric (barring machinist/machine error) they dont machine the out side first it goes frome inde to out side so its concentric(ie so as the round parts is round parts!)