bName: ______

AGEN 105: Lab 7 Part I

Ballasting & Weight Distribution

Reference:

(This is an Cooperative Extension Bulletin from Kansas. It provides good information on ballasting an agricultural tractor.)

  • There is another publication on ballasting on the Q Drive

Introduction:

Ballasting is an important issue in order for an agricultural tractor to operate up to its full potential. An operator can have a tractor that is sufficient in horsepower to perform a job, but if the horsepower cannot be efficiently transmitted to the ground, then there is a problem. Years of research has given agricultural engineers and equipment manufacturers the following information in regards to how a tractor can be correctly set up to be the most efficient in the field.

Tractor Design / Front (%) / Rear (%)
2 wheel drive - trailing implement / 25 / 75
2 wheel drive – semi-mounted implement / 30 / 70
2 wheel drive – mounted implement / 35 / 65
Front wheel assist (MFWD) / 40 / 60
4 wheel drive (articulated tractors) / 60 / 40
Skid steers / 30 / 70

The chart above was taken from the Wisconsin Extension Bulletin and contains information that is available from many different sources.

An aspect that is often not considered when discussing ballasting is that under ideal conditions an agricultural tractor operating in the field should have between 5 – 20% wheel slippage. There are many reasons why this is the case. Another issue while ballasting a tractor is keeping in balance maximum pulling power while providing long life to the drivetrain and tires. Ballasting a tractor can be done in many different ways and there are benefits and limitations to each.

Exercise:

  • Set up portable scales.
  • Weigh front of tractor
  • Weigh rear of tractor
  • Calculate total weight
  • Calculate weight distribution

Front weight (%) = front weight (lbs)/total weight (lbs) * 100

Rear weight (%) = rear weight (lbs)/total weight (lbs) * 100

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Tractor / Front Tire Size / Front (lbs) / Front PSI (theoret) / Front PSI (actual) / Rear Tire Size / Rear (lbs) / Rear PSI (theoret) / Rear PSI (actual) / Total (lbs) / Front (%) / Rear (%)

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Questions:

  1. What are the tire sizes for all of the machinery that we observed in this lab?
  1. Describe the following tractor styles in regards to their drive trains:
  2. Two wheel drive (2WD)
  3. Mechanical Front Wheel Drive (MFWD)
  4. Four Wheel Drive (4WD)
  1. What is the Horsepower to Weight ratio for each:
  1. Table 1 of the handout entitled “Getting the Most From Your Tractor” gives guidelines for Optimum Total Tractor Weight. Do the agriculture tractors fall into the correct range? What speed could each tractor be operated at considering the weight per horsepower?
  1. Using the information from the table listed in question 2, why do 2wd tractors need less horsepower per pound than MFWD or 4WD tractors?
  1. Does the weight distribution change on the loaders when the loader is raised? Why? Where would the tractor be set for the most traction? (with the loader up or down?) Why? Were the two tractors set up appropriately?
  1. Why does a skid steer have a 30:70 weight distribution? (more of an answer is needed than “cuz the engine is in the back” please!!)
  1. On a two wheel drive tractor why is it necessary to consider the weight on the front axle?
  1. Why is it necessary to have a greater percentage of the weight on the front end of a MFWD tractor than a two wheel drive tractor?
  1. Why does a four wheel drive tractor have more weight on the front axle than on the rear axle (unlike all of the other examples on the chart)?
  1. What are the items that are used for ballasting a tractor?
  1. Why is tire slippage (tire to ground, not front to rear slippage) a good thing for an agricultural tractor?
  1. What is the difference between a MFWD tractor and a four wheel drive tractor?
  1. What are the factors involved in adding liquid weight to tractor tires? What substance is usually used?
  1. Why do the ideal slippage figures vary from 5 – 20%? Under what conditions?
  1. Proper ballasting affects tractor performance greatly. List 5 things that ballasting affects and explain how the item affects it.

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