Ground Pressure 2

Discussion in 'Heavy Equipment & Pavement' started by TNdigger, Apr 14, 2008.

  1. TNdigger

    TNdigger LawnSite Member
    Posts: 10

    Can anyone tell me how to figure ground pressure of a S185 for comparison to my eariler post. Again I will ask to everyone what I m comparing is 8915lbs @5.0psi and 7890lbs @3.7. The heavier is a case 440 CT and The lighter is Asv SR 70. This will be my first big machine purchase so all advice is appreciated. Just to let you know Bobcat dealer?-poor service Cat dealer? -to proud. All others are not a consideration for me. Disposables. Thanks Again
     
  2. Scag48

    Scag48 LawnSite Fanatic
    Posts: 6,067

    I can't give you an exact number, but the tracked machines, while heavier, are going to have less ground pressure than an S185 due to a much larger ground contact area via the tracks. Maybe someone else knows better than I, but I'd take a stab and say a wheeled machine, such as the S185, is probably around 8-9 PSI. I know it's going to be greater, I'm just not sure by how much. I'll do some number crunching here in a minute and post anothe reply.
     
  3. Scag48

    Scag48 LawnSite Fanatic
    Posts: 6,067

    Okay, pulled up some specs. Case 440CT has 56" of track on the ground, per side. ASV SR70 has 71" of track on the ground, per side, and ASV provides the square inches of track on the ground, which is around 2,100 square inches.

    Now, an S185 weighs about 6,200 pounds, substantially lighter in comparison to the Case and ASV. Case 440CT is 8,900 pounds or so depending on how it's equipped, SR70 is 7,900 pounds.

    Figure a standard tire for the S185 is 12 inches wide and 16 inches around. Figure half the diameter of the tire is on the ground, could be more, could be less. So, 8" multiplied by 12" is 96 square inches per tire, multiplied by 4 tires is 364 square inches of contact. Divide that number by 6,200 pounds and the PSI for an S185 is around 16. Pretty large number, it's kind of surprising. This is all assuming that my tire calculations are correct, figuring out exactly how much tire is on the ground is the hard part, the math from there is easy.
     
  4. AWJ Services

    AWJ Services LawnSite Platinum Member
    from Ga
    Posts: 4,276

    A tired machine will do leave much deeper impressions in the ground.
    My Machine weighs close too 10k and I go across lawns quite often.It leaves lug marks more than ruts.
    It will leave depressions if the ground is soft enough too move under your foot.
     
  5. Digdeep

    Digdeep LawnSite Bronze Member
    Posts: 1,840

    Ground pressure= machine operating weight/total square inches of track surface.....SR70 7890/2100=3.75psi. A rough rule of thumb for a skid steer is that the ground pressure will be pretty close to the air pressure of the tires.
     
  6. raschmid07

    raschmid07 LawnSite Member
    Posts: 122

    TN Digger- Can't help you on your post, but were are you located in Knoxville? I'm from there but go to Auburn, I'll be heading back that ways for work this summer here in a few weeks.
     
  7. hansondirtman

    hansondirtman LawnSite Member
    Posts: 49

  8. ksss

    ksss LawnSite Fanatic
    Posts: 7,131

    I had read somewhere that the average pounds per square inch on a skid steer was around 35 psi, a lot of variables in that so I don't know how accurate that is.
     
  9. Digdeep

    Digdeep LawnSite Bronze Member
    Posts: 1,840

    I think that if the sidewalls are more rigid it adds a couple psi to the equation.
     
  10. Digdeep

    Digdeep LawnSite Bronze Member
    Posts: 1,840

    I think you're right ksss.
     

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