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!

Homework Help: Racecar Statics and Mechanics of Solids problem

  1. Nov 1, 2011 #1
    1. The problem statement, all variables and given/known data
    So I am designing the suspension for a small formula car. It's a pushrod suspension much like what is shown below:
    [PLAIN]http://f1-dictionary.110mb.com/Images/pullrod_poshrod_push.gif [Broken]
    I am trying to find the required tubing diameter for the loads the car will experience.

    2. Relevant equations


    3. The attempt at a solution
    The free body diagram

    The car is assumed to weigh 700lbs, have 60-40 front to rear weight distribution and be in a 2G turn, so the maximum force of the tire is 525lb. θ is assued to be 45°

    By the method of joints:

    At pinned joint A

    At pinned joint B

    So Fp=Ft/sin(θ)

    And the maximum force in the pushrod is around 743lb. One of the tubing thicknesses under consideration is 5/8 .035 4130 chromoly which has a yield strength of 70PSI.

    Cross sectional area is
    ∏/4(.625in-.59in)=.0275 in2

    Calculating the stress at maximum load is calculated at around 27000 PSI :eek:

    I know my statics is rusty but this is wayyyyy off. This tubing thickness is within the range of what other people are using, maybe a bit on the small side. Can anyone point out where I may have gone wrong?
    Last edited by a moderator: May 5, 2017
  2. jcsd
  3. Nov 1, 2011 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    The cross sectional area of the tube is incorrect: A = (pi/4)*(do^2 - di^2)
    The min. yield strength for this material is 70000 psi (70 ksi), not 70 psi.
  4. Nov 4, 2011 #3
    Thanks! makes much more sense now.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook