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Thread: Wheel nut torque measurement

  1. #1
    Abhishek Saxena
    Guest

    Wheel nut torque measurement

    Hello All

    This is my first post in this forum. I am trying to understand the behaviour of wheel stud in the wheels of a vehicle. I am mainly concerned about wheel nut torque. My questions are as follows:
    1. The mentioned torque is wheel tightening or wheel loosening torque?
    2. What is the behaviour followed by wheel stud when the vehicle is moving. Do they get tightened or loosened, in what pattern?
    3. What are the main factors on which tightening and loosening torque depends on?
    4. Why always wheel nuts are tightened and loosen in cris-cross positions?
    5. It is always said to measure torque values in ambient temperature conditions. What will happen to the torque values if we measure them in hot and extremely cold conditions.

    Thank you

    Regards
    Abhishek

  2. #2
    Associate Engineer
    Join Date
    May 2012
    Posts
    8
    Hey Abhishek,

    Here are my thoughts. I am by no means an expert, but this is what makes sense to me.

    1. Wheel nuts are usually tightened with a torque wrench set at a particular torque. It is probably what you are calling "wheel tightening torque".

    2. The wheel stud experiences shear when the vehicle is sitting still or moving straight. It is under tension when the vehicle is turning. If you're looking straight at the tread of a tire, there is a sideways force at the bottom of the tire. This creates a torque about the center axis of the wheel, which is reacted by the wheel nuts. This shouldn't loosen the nuts by itself. Nuts usually loosen because of vibrations. If you use the correct torque spec, you shouldn't have an issue with nuts loosening.

    3. Some factors that come to mind are the load that the nut will experience, and if anything (bearings?) need to be preloaded by the nuts. Someone else may be able to give you a better answer.

    4. This ensures that the wheel sits flat and concentric on the hub. If you tighten one nut all the way down, there's a good chance the wheel will be crooked. If you tighten the other nuts at this point, you are basically jamming a cylinder into a bore at an angle...you will probably score the walls of the bore.

    5. Dimensions of a part expand linearly when they are hot and contract when they are cold. The way the torque values change will depend on the materials of the stud and nut. If the stud has a higher expansion coefficient than the nut, the torque value should increase as it gets hot. Likewise, if the stud has a lower expansion coefficient than the nut, the torque value should decrease as it gets hot. The greater the difference between expansion coefficients, the greater change in torque values you will observe.

    Hope that helps
    Mike

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