[s-cars] RETorquing wheels

[QSHIPQ at aol.com]

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