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coefficient of friction and tires

Discussion in 'Technical Chat' started by 08pretaco, Feb 28, 2010.

  1. Feb 28, 2010 at 7:30 PM
    #1
    08pretaco

    08pretaco [OP] Almost there

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    if anyones interested in this info i came across, by all means.

    i came across while looking into a narrow tire vs. a wide tire. the argument was that the wider tire, due to more surface area acting on the other material (ground), would have more traction because there was more grabbing potential.

    this statement in fact if false and heres a good little read about frictions and such.

    http://www.school-for-champions.com/science/friction_coefficient.htm

    And some more reading if you feel frisky haha

    "A wonderful example of "In theory there is no difference between theory and reality. In reality however, there is."

    The total friction may be the same, but there will always be more available traction offroad with a narrower tire. It's about loading, a larger footprint has a lower pressure on the ground for each square inch of the contact patch, therefore is easier to break loose. You will do much better in mud and dirt with skinnies - they dig down in mud and may better find something to bite on, and on dirt or whathaveyou they put more weight on the tread to get grip and keep you moving. With harder surfaces it can go either way. In sand, the narrower tire's better bite will dig holes - not good. So wider - assuming you get wide enough to provide some flotation - will probably be better. On snow, narrower tires give a better bite and better traction - but in Deep snow, wide enough to provide flotation might be best (gotta go REAL wide though!) Also note that larger diameter tires increase the footprint too, and mathematically/geometrically allow for a better climbing, final gearing being the same. Whether wide tires or narrower tires are better for your type of wheeling is the issue each has to decide. Like most things, there is no "best" answer - it's all relevant."
     
  2. Feb 28, 2010 at 7:33 PM
    #2
    SoutheastTaco

    SoutheastTaco Resident Jackass

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    This exactly why i run 255's
     
  3. Feb 28, 2010 at 7:34 PM
    #3
    08pretaco

    08pretaco [OP] Almost there

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    this is why i chose 255's gotta save up the few bones and figure out which ones to run. post a picture of your ride with tire for me! what kind are you running?
     
  4. Feb 28, 2010 at 7:34 PM
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    ktmrider

    ktmrider Senior Member

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  5. Feb 28, 2010 at 7:36 PM
    #5
    carmellocafe

    carmellocafe Begin With The End In Mind.

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    Well said Oliver. Agreed. :thumbsup:
     
  6. Feb 28, 2010 at 8:03 PM
    #6
    08pretaco

    08pretaco [OP] Almost there

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    i was looking at the tread depth on the coopers...only 18/32's
     
  7. Feb 28, 2010 at 8:07 PM
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    SoutheastTaco

    SoutheastTaco Resident Jackass

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    im running 255 75 17 bfg mud terrains, They were built for the rubicon jeeps the tread is slightly different look them up on tirerack. i will post some pics when i get the chance to take them.
     
  8. Feb 28, 2010 at 8:10 PM
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    08pretaco

    08pretaco [OP] Almost there

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    im trying to stay away from mud terrains since the set i had before only lasted me 25k and i do alot of freeway driving
     
  9. Feb 28, 2010 at 8:12 PM
    #9
    SoutheastTaco

    SoutheastTaco Resident Jackass

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    i put mine on when the truck was new ive got 14k on it now they still have like 85-90 left they are wearing really good.
     
  10. Feb 28, 2010 at 8:14 PM
    #10
    08pretaco

    08pretaco [OP] Almost there

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    ya but after talking to chris and searching, mud terrains hardly (from what i found and heard) last their thread life. they start going to shit at a certain amount of miles
     
  11. Feb 28, 2010 at 8:18 PM
    #11
    SoutheastTaco

    SoutheastTaco Resident Jackass

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    what size rim are you running?
     
  12. Feb 28, 2010 at 8:20 PM
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    08pretaco

    08pretaco [OP] Almost there

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  13. Feb 28, 2010 at 8:24 PM
    #13
    SoutheastTaco

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    look at the cooper discoverer s/t you can find them in a 255 85 16 for around 165 a tire
     
  14. Feb 28, 2010 at 8:26 PM
    #14
    08pretaco

    08pretaco [OP] Almost there

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    ya thats the thread deapth i found with the 18/32. doesnt seem very deep at all
     
  15. Feb 28, 2010 at 8:26 PM
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    SoutheastTaco

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    i think the km2's come in that size too..
     
  16. Feb 28, 2010 at 8:29 PM
    #16
    08pretaco

    08pretaco [OP] Almost there

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    i couldnt find an a/t from bfg in that size unfortunately. i really like the km2's but oh well ill have to settle, lots of people like them so it shouldnt that bad with such little tread depth
     
  17. Feb 28, 2010 at 8:31 PM
    #17
    SoutheastTaco

    SoutheastTaco Resident Jackass

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    its a really odd size but i think it will good
     
  18. Feb 28, 2010 at 8:31 PM
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    SoutheastTaco

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    i like the old school tall skinny look
     
  19. Mar 3, 2010 at 9:49 PM
    #19
    bmgreene

    bmgreene Well-Known Member

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    In theory, friction is only dependent on coefficient of friction (determined by the materials in contact) and normal force (load pushing the two together).

    In the real world, a smaller contact patch will "lose grip" under less total force because the rubber in the tire will reach its critical shearing stress at a lower total force acting through it, although tread patterns and shapes can factor in as well. Unless you're supporting weight with the steel in the tires (which in my experience is rarely good for tire life), the contact patch area will be the weight supported by a particular wheel (normal force) divided by tire pressure regardless of the width of the tire you're using.

    The reason for a narrower tire's "bite" or a wider tire's "float" will be due to the tendency to have higher pressure in the narrower ones and lower pressure in wider to control tire deformation (and the "rolling friction" and tire wear & tear that comes with it) during street driving, but with durable enough sidewalls, there's nothing to stop one from running 165s at 20 psi and develop the same size contact patch as 255s at the same pressure; the other thing about wider tires is that more of that bigger patch would consist of the treadwall as opposed to flexed out sidewall.
     
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