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Tyre width

  1. Apr 27, 2004 #1

    Clausius2

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    I was wondering me why the most powerful cars have usually tyres with a great band widht. Surely it is not a question of adherence, because friction factor is not a function of the contact area, but the type of surfices. Does it do with traction stability?. I have heard that F1 cars have reduced their tyre widht bands when running also in dry floor, in order to limit the speed. If they reduce the contact area then the traction force would be the same because friction factor is not modified. Thus, what is the true reason?
     
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  3. Apr 27, 2004 #2

    Cliff_J

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    By textbook or with real-world non-linearities factored in?

    The wider surface allows the tire to deal with surface imperfections and provide a larger contact patch. Also, non-fast cars would not be optimized for greatest traction for accelerating but instead optimized for efficiency, drivability, and most importantly cost.

    F1 cars have had many restrictions placed on them by the FIA to try to control and limit many things. Just a few years ago they switched to grooved tires to reduce the contact patch and the regulations only get more complex from there. Its still great racing, Honda is back in the game again while BMW is showing another good mid-season presence and Ferrari seems to be struggling to maintain its domination.

    Cliff
     
  4. Apr 28, 2004 #3

    Clausius2

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    You have forgotten somebody: Fernando Alonso!. The thrilling of the race is always caused by him. He is the best driver behind Schummy, but he has no enough engine to defeat Montoya or Barrichello.
     
  5. Apr 28, 2004 #4

    Cliff_J

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    True he's good, IIRC Alonso was the youngest driver to win a race last season (at what like 21? when schummie is the old man at 36) and they looked real competitive until Williams got their suspension sorted out. His little 'push' on Ralph last weekend was one of the better moments besides Coulthard's running into him - again - and then fighting to pass Minardis and Jordans without blowing up the motor.

    But I'd rate Montoya as second best out there, had the Williams' suspension been sorted out eariler last year Kimi would've been down in 3rd or 4th and Schummie might have been playing second fiddle to the blue and white...
     
  6. Apr 28, 2004 #5
    Oh, face it Michael schumacher is the best, and is only beaten when his car breaks down... Montoya will probably take over that position AFTER Schumi retires or challenges himself by joining some small team.

    On the the matter of the headlinesubject I'd like to ask: Isn't a wider tire a better tire for racingcars generally? The more drag can be overcome with enginepower, the heavier turning can be overcome with powersteering, the better grip gives more speed in corners, better acceleration... I see greater advantages than disadvantages... Or am I missing something?
     
  7. Apr 29, 2004 #6

    Clausius2

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    Hey, I disagree with you. More drag?, Better grip?, Why?. Does the friction factor (F=f*N) a function of contact area?. I don't see the advantages.
     
  8. Apr 29, 2004 #7

    Cliff_J

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    We're not sliding a concrete block across a smooth floor at 1m/s here, we're talking about a dynamic system where the friction factor will not be a single number. Think of it like a table on carpet and those little pads that make furniture easier to move. Does the slippery surface help, sure, but the wider surface area results in less 'sink' into the carpet where the small table legs had a lot of 'sinkage' so they almost create a mechanical lock. The surface of a roadway is far from perfect and will have some debris - a wide tire is increasing the chance of the tire surface actually touching the surface of the roadway.

    Also, the tire is deforming constantly as it touches the road, and this deformation and affect on friction factor does not seem to follow a linear relationship. As more force is applied to the tire surface the increase in pressure (force over surface area) will increase but the deformation will allow the two surfaces to mechanically interlock. At some point the interlocking action is complete and further force will not improve it. I use force instead of mass because a good race or stunt car driver knows that success is determined by shifting the car's weight to the appropriate tires at the appropriate times with accelerations.

    For the drag thing, you have aerodynamic drag and rolling resistance (drag) associated with the tire. A wider tire has more surface area presented to the air, and the deformation adds its own drag as well.

    If surface area was a non-factor, then the air pressure inside the tire wouldn't matter. But many people who decide to do burnouts and e-brake slides knows that over-inflating the tires will reduce tires ability to deform and the contact patch thus reducing the traction. On the flipside, a drag racer tries to balance low air pressure inside the tire for better starting traction with handling at top speed which suffers with lower tire pressures.

    A physics textbook offers many good formulas that should relate well to most examples one can think up. But until the non-linearities are addressed (and they typically aren't until calc-based physics) there will always be examples where a simple equation can be shown to inconsistent with real-world.

    Cliff
     
  9. May 1, 2004 #8

    Stingray

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    Tire friction is actually a very complex subject. Rubber doesn't behave anything like what they tell you in physics courses. To give you an idea of what's involved, engineers often use something called Pacejka's magic formula, which is an empirical relation involving ~30-40 free parameters (some versions are less detailed).
     
  10. May 2, 2004 #9
    Clausius2,
    If you really want to know what works in racing, the answer is pretty simple. Look at the winning cars. This will tell you what works, it just won't tell you why. Sometimes reading the official rule book or talking to someone from the team will tell you why.
     
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