[s-cars] RETorquing wheels

[Trevor Frank]

If it is properly torqued there is no shear load on the bolts, because
of friction, the tention load is used to stop the wheel from turning.
It is common to calculate up to 90% of the tention load as shear.  From
this it would be wise not to lubricate the mating surfaces of the wheel
and hub.  I have worked on a few porsches that have a 8 or 6mm flat head
that bolts to the hub and I guarentee that it was never ment to take any
shear.

-----Original Message-----
From: QSHIPQ at aol.com [mailto:QSHIPQ at aol.com]
Sent: Tuesday, October 15, 2002 7:05 AM
To: tedebearp at yahoo.com; quattro at audifans.com
Cc: s-car-list at audifans.com; v8 at audifans.com; urq at audifans.com;
200q20v at audifans.com
Subject: Re: [s-cars] RETorquing wheels


Teddy:
Comments inserted:
In a message dated 10/15/2002 7:20:44 AM Central Daylight Time,
tedebearp at yahoo.com writes:


>scott,

>i'm not convinced it's heat cycling.  i think your bolts may be
>exhibiting classic signs of fatigue.  they were stretching permanently,

>causing the torque to drop.  if i were you, i'd replace all of them
>immediately.

Maybe.  I doubt it, but maybe.  Thinking about all the folks that own
audis that consider a bolt a lifetime part Teddy.  IME, usually in a
"fatigue" state, a bolt won't pass thru a die cleanly.  These do.  I
also swapped the front bolts for the rear bolts, the rears were at spec
when I did so, and remained at spec thruout my experiences with the
front.  This also wouldn't explain the fact that after 4 retorques, all
subsequent cks indicated no change.

>are your spacers hubcentric?

No, the wheels are, the spacers aren't.  FYI, we use these same ones in
the rally car without incident (knock knock).

> do they provide a flange for the wheel to
>pilot on?  are they doweled or screwed to either the hub or the wheel,
>to eliminate a shear plane from brake/drive torque?

The wheel rests on the hub, not on the spacer or the wheel bolts.

>the bolts/studs are
>not meant to bear the weight of the car.  they're supposed to be loaded

>in tension and in shear (against brake/drive torque).  and some
>manufacturers will have you screw the rotor to the hub to eliminate
>shear loads on the bolts/studs.

I'm not aware of that at all.  Many a Volvo and VW have a single set
screw that keeps the rotor holes oriented to the hub holes.  That set
screw can't take any sheer load, it wasn't meant to.

>the weight of the car is meant to be borne by the wheel and hub
>interface.  if the wheels are not hubcentric, that means the studs are
>loaded in bending, and this load is fully reversed twice every wheel
>revolution.  the use of a spacer makes this worse, by moving the load
>further outboard and increasing the moment.

Ok, but the wheels are hubcentric.

>even if the wheels are hubcentric, the spacers result in the addition
>of a second shear plane under braking.  you now have an interface
>between the hub and rotor, and between the rotor and wheel.  that's why

>i asked about dowels and screws

Agree in theory.  The dowels and screws usually aren't seen, but
bolt/hubcentric spacers usually are (porsche).  IME with the Dodge
turbos (remember when dodge 2.2t went from a 4 bolt wheel to 5 bolt
wheel? - sheered the 4bolt wheels alot), 5 bolts on a quattro wheel
should be plenty to keep sheer to a minimum.  Sheer is a risk, but you
usually see that in evidence by thread imprints on spacers, brake hubs
etc.  Not evident here, even on the universal spacer used.

>i really don't like spacers for the above reasons.

I've never liked them.  But the wheels won't fit over the brakes without
them.  That said, in this case, the spacer isn't THE problem.  I believe
this was a force majeur due to just the right combination of factors,
including weather and a lot of right turns.

>as for the M3 guy, were his wheels stock?  were they hubcentric?  he
>might just not have torqued them properly at some point, resulting in
>bolt failure.

I never spoke  to him Teddy.  So with neither of us there, tough to
speculate.  However, I'd betcha if both he and I had this experience
before, nothing would have happened that day.  Avoiding this is pretty
easy, take a run and ck torques.  Unfortunately for me, my first run was
the culprit. Thankfully, when I knew something was gettting VERY wrong,
I was already crawling.  The M3 guy was AT speed.  That's scarey.

>i'd replace the bolts, and get rid of the spacers.  if you can't get
>rid of the spacers, make the bolts a maintenance item and replace them
>regularly.

I'll replace the bolts, cuz I have another set.  In no way will I
consider that to be enough.  I have no choice on the spacer, so they
have to stay for a while.  Tho I appreciate you taking the time to think
on this a while, I'm still convinced this can "happen" if conditions are
right.  Even with all your preventive ideas above, in the end, the
bottom line remains the same: Routine cks of wheel bolt/nut torque in a
performance theatre is the best medicine, and really, the simplest of
solutions.

I'm only putting all this up to make folks aware, not speculate on the
failure.  Anyone that knows me, knows I own a plethora of torque
wrenches, and use them often.  And this still happened.  What I'm more
concerned about is the high percentage of track attendees that don't
even own a torque wrench.

HTH

SJ



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