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Thread: Center lock wheel nut thread direction

  1. #1
    I know the thread directions for center locks are meant to be left handed on the right and right handed on the left.
    What I don't know is why. Initially I thought it was to do with the torque under braking or acceleration, but as they are not different front to rear this, from my logic cannot be the case. The only explanation I have heard is that it has something to do with the thread clearance between the nut and the spindle. As the wheel rotates, because the spindle is slightly smaller, with each rotation it rotates slightly more than the nut- think hula hoop. This eventually leads to the nut loosening off if it is threaded in the wrong direction.

    I am still not 100% sold with this explanation so was wondering what reasoning other people have used to determine the thread direction for their center locks
    Curtin Motorsport 09-12
    2009- Impact Attenuator, General Annoyance
    2010- Pedal Box
    2011- Intake and Exhaust
    2012- Intake, Exhaust and Unsprung

  2. #2
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    Search nut precession, there are a few videos on it that explain it quite well on youtube, it has more to do with the wheel flexing and providing clearance progressively around the nut, slowly working it off. Our nuts have normal threads and we haven't had issues with precession (until tightening torque isn't high enough and wear comes into play..)
    ex-UWA Motorsport

    General team member 2013-15, Vehicle Dynamics Team Lead 2012
    Project Manager 2011, Powertrain minion 2009/10

  3. #3
    Centre lock nuts are evil. They will get you in your sleep. Beware...


    Bewaaare....
    Dunk
    --------------------------------------------------------
    Brunel Racing
    2010-11 - Drivetrain Development Engineer
    2011-12 - Consultant and Long Distance Dogsbody
    2012-13 - Chassis, Bodywork & Aerodynamics manager

    2014-present - Engineer at Jaguar Land Rover

  4. #4
    Originally posted by Dunk Mckay:
    Centre lock nuts are evil. They will get you in your sleep. Beware...


    Bewaaare....
    haha
    Regards
    Jon

  5. #5
    Cool thanks nick that makes a bit more sense
    Curtin Motorsport 09-12
    2009- Impact Attenuator, General Annoyance
    2010- Pedal Box
    2011- Intake and Exhaust
    2012- Intake, Exhaust and Unsprung

  6. #6
    I can't think why it would be different for centre lock nuts, but standard practice for normal wheel nuts is LH thread on LH side. I have experienced wheels coming loose on cars a couple of times and it was always LH side (with RH threads of course)

  7. #7
    IMO, best approach from a practical and logistical standpoint is to just use the same threads (RH) all around the car... with a castled wheel nut and clevis pin, or some other positive lock.

    You have to have the positive lock there by rule anyway so I'd say take advantage of that, let the thread direction be a non-issue, and make it easier for manufacturing and carrying spare parts.

  8. #8
    An small experience / story to share. Several years ago, I worked for a racing team who was using 2 heavy mechanics and a leverage of 2.5 meters to tight the wheels (don't even think about the torque number!) ... and they still manage to lose some of them on the race track!

    The issue was simply that the thread of the hub and the wheel nut was too fine. Simply think about the amount of the torque that will be translated in a force perpendicular to the rim, holding it against the hub flange or brake disc. A simple calculation that the race car manufacturer did not do. In a panic, the team had to re-machine its own hub and central wheel nut after 2 races of the season. With a bigger pitch number they never had any problem.
    Claude Rouelle
    OptimumG president
    Vehicle Dynamics & Race Car Engineering
    Training / Consulting / Simulation Software
    FS & FSAE design judge USA / Canada / UK / Germany / Spain / Italy / China / Brazil / Australia
    [url]www.optimumg.com[/u

  9. #9
    The issue was simply that the thread of the hub and the wheel nut was too fine. Simply think about the amount of the torque that will be translated in a force perpendicular to the rim, holding it against the hub flange or brake disc. A simple calculation that the race car manufacturer did not do. In a panic, the team had to re-machine its own hub and central wheel nut after 2 races of the season. With a bigger pitch number they never had any problem.
    Is it possible that you accidentially mixed things up?

    If a screw/bolt/nut loosens, you need a finer thread. This is because with a fine thread an axial force produces less torque that tries to loose the nut. In the case of an infinite fine thread, the "ridge" is perpendicular to the bolt axis which means that no loosening torque is produced at all.

    In the metric system, the thread is described by outer thread diameter and pitch, in the imperial system it is outer thread diameter and threads per inch. If the thread is fine, the pitch value is low, like in M8x1,0 instead of the regular, coarser M8x1,25. With a low pitch value the value of threads per inch increases, leading to a "bigger pitch number" as you described it.

    So their problem was not a thread that was too fine but a thread that was too coarse ...
    Tilman Schröder
    GETracing Dortmund, alumnus
    University of Technology Dortmund, Germany

  10. #10
    Senior Member
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    penna,

    The "correct" thread direction depends on relative clearance between wheel-and-nut, and between nut-and-thread. Briefly, each of these, together with wheel-to-hub "fretting", work to loosen the nut in opposite directions. So the answer to "RH or LH?" is "It depends...".

    Gruntguru is right in saying that left wheels fall off much more often when done up with RH threads. exFSAE is right in saying that logistically it makes more sense to use RH all-around. Claude is right in saying that you can do conventional centrelocks up to stupendously high torques and they still fall off...

    Anyway, last year I ranted on this subject at great length on the "Center-lock hubs and wheels" thread. That thread started in 2004, but picked up again (page 4) in 2011 here

    There are some sketches about half way down page 6 that solve most of the problems (IMO). But read the posts...

    Z

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