Re: [ihc] Dual wheel bearings

[bearbvd@xxxxxxxxxxxxxx (Greg Hermann)]

At 1:43 PM 5/10/04, Jim Grammer wrote:
>>Date: Mon, 10 May 2004 14:10:35 -0600
>>From: bearbvd@domain.elided (Greg Hermann)
>>Subject: RE: [OLDIHC:] Re: [ihc] wheels again, dual>single conversions?
>
>>Ed--
>
>>The wheel bearings are in the SAME location relative to the tire's contact
>>patch--and the track is the same-- the only differences are the lateral
>>location of the  wheel mounting flange on the hub and the backset of the
>>wheel.
>
>>There is no change at all in the bearing loading or the steering geometry
>>when the correct wheels are used with the correct hubs. It's when you start
>>swapping from single to dual type wheels without understanding all the
>>details that the trouble starts---
>
>>Greg
>
>Ah, professor....please elucidate, this is most counter-intuitive ;0
>
>Understood about the relative positions of bearing and contact patch,
>however that contact patch acts on the bearings through a greatly lengthened
>lever arm(distance from bearings to wheel mounting surface). What are we
>missing?
>
>Jim

First of all, Grasshoppah, given some of my recent experiences with a
perfesser, callin' me that might well getcha smacked upside da head if you
were within reach !!

Try looking at the tire/wheel/hub assembly as a 'black body'--the road
pushes up against it at the center of the contact patch, and the wheel
bearings push down on it wherever they are. The load on the two wheel
bearings simply does not change, no matter whether the wheel is connected
to the hub at the centerline of the contact patch, or even a foot or two
outboard of it, so long as the contact patch is in the same relative
location relative to the bearings.

What DOES change as the backset of the wheel is increased and the wheel
flange part of the hub are moved outboard are the forces (and stresses) in
the wheel center and the hub flange. There is a considerably higher moment
at the connection between wheel center and hub flange with a dual wheel
than there is with a single wheel.

This moment (and the higher inward and outward forces on the lugs
themselves which it produces) are PRECISELY the reason why one HAS GOT to
be so much more retentive about torquing the lugs on dual wheels properly
if you don't like having 'em come loose and/or break !!

I knew from the git-go that I would be pretty likely to overload my 1300.
That's perzactly why I upgraded it to 5/8" lug studs !! (I _WAS_ right
about what I was gonna do, as well! ) :-)

Greg