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Friction & tyres

  1. Sep 1, 2008 #1
    Friction between 2 surfaces is independant of the area of contact and depends only on the nature of the two materials right?
    Then why do thicker car tyres give better grip?
     
  2. jcsd
  3. Sep 1, 2008 #2

    mgb_phys

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    Because they are made of softer rubber. To make up for the greater wear you have to have more of it to give a reasonable life.
    Good question - most people don't really believe the law about friction being independant of area!

    On motorbike tyres there are also secondary effects, you want a larger size to make sure that the entire contact path isn't resting on the same pit of gravel.
     
  4. Sep 1, 2008 #3
    Why does softer rubber grip better?

    If thicker tyres are made of softer rubber, then wont the diameter of the tyres reduce faster? So how does having more rubber make up for greater wear and tear?
     
  5. Sep 1, 2008 #4
    You can not apply the friction law to the case of tires totally. To have the formula F=u*P (without area), the surface must be very smooth and dry.
    You tires and the road surfase probably are not in that ideal condition.
     
  6. Sep 1, 2008 #5
    If its not friction between tyres and the road, it ll be friction between the tyre and something between the tyre and the road.. In any case, that friction too will be independant of area..
     
  7. Sep 1, 2008 #6

    rcgldr

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    Not in the real world, only in an idealized situation.
    Because of tire load sensitivity, thicker tires reduce the load per unit area:

    http://en.wikipedia.org/wiki/Tire_load_sensitivity
     
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