[s-cars] RETorquing wheels
tedebearp at yahoo.com
Tue Oct 15 00:31:43 EDT 2002
--- QSHIPQ at aol.com wrote:
> Sunday, I casually mentioned to a former student standing by that I was
> looking for a 14x1.50 tap. "I've got that"!!! The three stage type no less.
> Within 10 minutes I was back on the track. I ran 15minutes of my 30 minute
> run, and came back in to ck the torque. Easily 20ft/lbs down! 15minutes,
> down another 10. Yikes! Finally on the 4th retorque I was good for the rest
> of the day on the left side.
> Conclusion? Not really sure, other than the combination of wheel aluminum,
> spacer aluminum, aluminum hat and steel hub, steel bolts and cold weather
> might have created heat cycles that backed out the bolts. I was routinely
> pulling the right side wheel off after every run to ck pad wear, and needed
> to retorque the wheels per the above routine. I had a race buddy that hated
> spacers, I'm gettin there quickly....
> Another driver had a wheel leave his car yesterday, stock M3 no spacer, on
> track, he had to walk a lot further to retrieve his (insert more jokes at me
> sharing my torque methods). Michelins Mr. Green :)/, so those sumitomo
> Moral: You can't recheck torque on the wheels enough at a track venue, race
> or marque event. If you *don't* have a torque wrench, get one. If you do,
> use it often.
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.
are your spacers hubcentric? 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 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.
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.
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
i really don't like spacers for the above reasons.
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'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
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