1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Rotational inertia of truck and trailer

  1. May 19, 2009 #1
    I need to compute the energy to get a truck and trailer from 0 to 60 mph from rest taking into account the mass of truck and trailer and inertia of wheels and rims.

    Do I treat the rims and tires as a cylindrical shell or solid cylinder? Once I find the energy of the tires and rims do I just add that to the 1/2MV^2 for truck and trailer?

  2. jcsd
  3. May 19, 2009 #2
    The moment of inertia of a cylindrical shell is mR2, while the solid cylinder is (1/2)mR2. The wheels are about 0.8mR2. For an automobile, the rolling tires add about 4% to the dynamic mass e.g., kinetic energy KE = (1/2)(1.04) mv2, where m is the static mass.
  4. May 19, 2009 #3
    By wheel you mean tire and rim? Then I could use 0.8MR^2 to approximate the inertia instead of treating it separately as cylindrical shell and solid shell?

    Does this approximation apply to all passenger car and truck tires?

  5. May 19, 2009 #4
    Yes, the tire and rim together are about I = 0.8 mR2. The 18 tires plus rims (=wheels) are only a small percentage (<5%) of total truck & trailer mass.
    So the kinetic energy of a wheel is
    KE = (1/2) I w2 = (1/2)(0.8)m (Rw)2 = (2/5) mv2 (rotational energy only)
    For 18 wheels it is
    KE = (36/5)mv2
    This gets added to the total vehicle kinetic energy:
    kE tot = (1/2)Mv2 + (36/5) mv2
    How much do the wheels weigh (mg)? 200 pounds?
  6. May 20, 2009 #5
    The wheels weigh 200 lbs for steel rims and 170 lbs for aluminum rims.

    Thanks for the info.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Threads - Rotational inertia truck Date
I Question about torque and center of mass Jun 30, 2017
I General approach to find principal axes of rotation? Apr 27, 2017
I Rotational Inertia Apr 26, 2017
I How to simulate rotational stability of multiple parts? Dec 23, 2016