[s-cars] RETorquing wheels

Trevor Frank tfrank at symyx.com
Tue Oct 15 16:45:18 EDT 2002

You might be right on getting movement, but lets hope not.  A properly
designed bolted union is one that has the tention in the bolts way in
excess of the forces that would ever act on it.  This means that once
you have bolted it together you have gone up on the stress strain curve
to a point that will not be exceeded.  If it is exceeded and often then
you get into a situation where you can have a fatigue falure, bad
design.  If this was the case then you have one of two options, increase
the torque "tention" and or at the same time go to a stronger bolt and
increase the tention.

I do agree that you might be seeing localized yeilding of the aluminum,
spacers or more likely the rims.  Expecially under heavy breaking and
increased temps.  Look at the strenght of aluminum at 400 deg F.  I
think Ted is right on with tighten, eventially you should reach a point
where the density of the aluminum is to a point where you shouldn't have
this problem.

Moral of the story, buy rims that have been forged.

-----Original Message-----
From: Theodore Chen [mailto:tedebearp at yahoo.com]
Sent: Tuesday, October 15, 2002 2:18 PM
To: Bernie Benz; s-cars
Cc: 200q20V mailing list
Subject: Re: [s-cars] RETorquing wheels

--- 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

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

> 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.


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