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Effect of wheel diameter in a car

  1. Jul 17, 2014 #1
    Hello guys

    I want to know how the wheel diameter of car affects the car's performance parameters(physical significance) such as

    I would also appreciate if some equations are used to substantiate the physical understanding of these.
  2. jcsd
  3. Jul 17, 2014 #2

    jack action

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    Just to make sure, are you referring to the wheel diameter or tire diameter ?
  4. Jul 17, 2014 #3

    Ranger Mike

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    Steering wheel or wheel for the tires?
  5. Jul 18, 2014 #4
    Thanks for replying . i actually mean the rim diameter
  6. Jul 18, 2014 #5
    wheel for the tyres.
  7. Jul 18, 2014 #6


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    Assuming the wheel material is denser than the rubber in a tire, then a larger wheel increases the combined weight of wheel and tire. Assuming a fixed outer diameter of a tire, the side walls can be either too tall or too short for optimal handling, depending on how stiff the sidewalls are. As an example, in the case of a car like a Porsche 911, a wheel diameter around 18 inches is usually optimum for racing tires, while a Formula 1 car uses a smaller wheel, and relatively taller and stiffer sidewalls.
  8. Jul 18, 2014 #7

    jack action

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    The following assumes the tire diameter stays constant.


    By modifying the wheel diameter, you will modify the total inertia of the wheel/tire assembly, thus affecting the acceleration of the vehicle.

    It may increase or decrease, depending on the shape and design of the wheel. Here is a calculator to get a crude evaluation for rotational inertia of wheel/tire.

    Tire stiffness:

    With a small wheel diameter, the vertical stiffness of the tire usually increases. This means that the tire radius will vary more under vertical load (such as weight transfer) (deflection = load / stiffness). This affects the force and speed measured at the contact patch (force = torque / radius; speed = rpm * radius).

    The preceding is also true for braking, which will affect front/rear brake bias.

    Having a higher tire vertical stiffness also means that the tire can loose contact more easily with the road - if it is relatively too rough - hence affecting handling.

    Similarly, the longitudinal stiffness will most likely decrease with smaller wheel diameter. This means that a very large acceleration/braking force can be absorbed, giving a smoother force transfer to the ground, like on drag tire for example:


    Tire rigidity:

    Having a smaller wheel diameter means a less rigid tire. This means that it is easier to remove the tire from the wheel under a lateral force, i.e. under lateral acceleration; A beadlock is then necessary.

    A more rigid tire usually also means lower rolling resistance.


    Also, as the wheel diameter increases (no matter the tire diameter), the force between the rim and the tire increases, which can lead to slipping; Again, a beadlock may be necessary.

    Finally, a larger wheel usually means more space for a larger brake system which can absorb more heat.
  9. Jul 18, 2014 #8

    Ranger Mike

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    we had a great discussion on mech engineering post

    Alloy wheels and fuel economy
    by Dr Lots-o'watts
    use search above to check it out..
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