[s-cars] RETorquing wheels

[Theodore Chen]

--- Bernie Benz <b.m.benz at prodigy.net> wrote:
> Ted,
>
> In your analysis below and in your previous post you have totally ignored
> the static friction between hub and wheel due to the torqued bolt clamping
> forces.  Even if the hub were greased there would be no torque or weight
> induced bending loads on the lug bolts because this clamping friction is
> great enough to retain total control, even with loosely torqued bolts, down
> to a point.

you're right, i forgot to account for the friction, which certainly makes
a big difference.  so much for late night epiphanies.

however, you get that friction only for as long as you have clamping
loads on the bolts.  normally, bolt tension is intended to ensure that
the bolt never loosens.  in this case, you're relying on the bolt tension
to provide the clamping force needed to produce the friction.  the total
clamping force can and does change as wheel loads change rapidly (side
loads may counteract the clamping force) when you are out running on the
track in a 2-ton car with sticky tires.  at some point, the net clamping
force is reduced enough for you to get some wheel movement.

i tried a 1/4" hubcentric wheel spacer many years ago on a mustang with
freshly-installed 5-lug hardware.  after a few hundred miles of street
driving, there were obvious signs of fretting wear between the spacer
and hub.  all of the lug nuts had been torqued to 90 lb-ft. and rechecked
after 50 miles.

at that point, i decided to revise my setup, and continued to drive the
car on the street.  at about 1000 miles total, the wheels and spacers
came off and i revised my brake setup so i wouldn't need the spacers
any more.  inspection showed that the fretting wear had continued.

> The basic problem is with the aluminum wheel material.  Unlike steel,
> aluminum has no yield point, below which it is truely elastic.  Therefore it
> will permanently deform until the bolt loading is sufficiently reduced
> and/or the loaded area is sufficientlly increased that continued deformation
> becomes negligable.  Every time the wheel is remounted, to a different
> position relative to the hub and with a different bolt in each hole the
> process starts all over again.

depends on the wheel.  some wheels do have pretty soft aluminum alloy.
but since pitching the spacers, i've never had to retorque my lug nuts
after mounting the wheels - and yes, i check quite often when i'm at
the track.  i've run a lot of different race tires, including slicks at
one point.

> So, just keep torquing Scott!  Grease your bolts, threads and heads.  You'll
> get more clamping force out of them for a given torque and thus reach
> equliberium sooner.

there are lots of people who use wheel spacers on track cars with success,
but my observation is that they tend to be driving small, light cars.
a 2-ton audi is not a small, light car.  i've seen enough people lose
a wheel on the track to convince me that's not something i want to happen
to me.  most people will never have problems with wheel spacers.  the ones
that do tend to find out the hard way.

scott was very lucky that the loss of a wheel didn't result in the
destruction of his car, or worse, serious injury to himself.  if he
wants to continue using wheel spacers, he should at least give some
thought to using dowels or screws to eliminate one of the shear planes.

as for me, wheel spacers will never find a home on my track car again.

you pays your money, you takes your chances.

-teddy


__________________________________________________
Do you Yahoo!?
Faith Hill - Exclusive Performances, Videos & More
http://faith.yahoo.com