Factors
Influencing Grader Road Loping
Lope (Bounce) is a natural phenomenon
in motor graders occurring at resonant speeds that correspond
to the natural frequency of the vehicle/tire/wheel unit.
Many grader attachments and configurations affect the
nature and frequency of the bounce. Other factors include:
- Weight
Distribution of the Motor Grader
- Inflation
Pressures
- Tire
Size
- Road/Operating
Conditions
- Out
of Round Rims and/or Tires
Each
of these conditions can act alone or combine to change
the natural frequency of the system, thus changing the
speeds at which lope occurs and the intensity of the
disturbance.
How
to Solve Motor Grader Road Loping
1. Evaluate the Basics:
- The
roundness of the tire/rim assembly
- Uneven
Wear
- Flat
Spots
It
is normal for Bias ply tires to develop flat spots from
sitting for extended periods of time. This can affect
ride since the roundness of the assembly is deformed
(possibly up to 0.4 inches). Prior to operating the
machine in finish grading conditions or measuring tire
roundness the machine should be run for an appropriate
period of time to warm the tires up.
2.
Configure machine to design weight distribution:
Field testing shows that vehicles with an actual weight
distribution matching the design distribution were easier
to correct than machines that had unevenly distributed
weights. Design load distribution for OE Motor Graders
tend to be 33% front and 67% rear. Testing has shown
that correct weight distribution combined with other
factors lead to the best improvement in ride. At worst,
the machine should have a weight balance of 30% front,
70% rear. Attachments such as rippers, scarifiers, pushblocks,
ROPS, etc. have a pronounced effect on the weight balance
of the machine and should be accounted for.
While
not always practical for machines in-service due to
the added expense of adding counterweights, work at
the OE level and the dealer level is important to see
that new machines are correctly equipped.
3.
Correct Inflation Pressure Settings:
The spring rate of a tire is related to the load and
inflation pressure of the tire. The best ride results
are achieved by setting the cold inflation pressures
to match the actual load per wheel position. It should
be noted, however, that these settings are for road
transport and light material finish grading only (the
common loping field conditions). For slope and ditch
work or extreme use, the air pressures need to be increased
from standard by 10 to 15 psi.
Example:
Grader GVW = 32,000 lbs. with weight distribution
of 30% front, 70% rear:
- Front
Tire Load = 5,280 lb./tire
Typical Air Pressure = 30-35 psi**
Correct Air Pressure = 24 psi**
- Rear
Tire Load = 5,360 lb./tire
Typical Air Pressure = 35-40 psi**
Correct Air Pressure = 25 psi**
**All
pressure settings are cold inflation for a 14.00-24
bias ply tire.
4.
Additional Solutions:
- Use
Larger Tires
Larger tires will allow greater loads to be carried
with less inflation pressure. The testing revealed
that the reduced air pressure requirements helped
the ride, while the larger tires provide more traction,
flotation and stability.
- Use
Radial Tires When Possible
Radial Tires, in addition to increased stability,
traction, flotation, and cut resistance do not suffer
from flat spots as do bias ply tires. This will save
the end user the burden and down time of warming up
a machine prior to finish grading.
In
Summary
Testing has revealed that the combination of weight
distribution, inflation pressure, and tire size had
the most dramatic effect on reducing road loping. When
possible all of these measures should be enacted; however,
the use of any one method or combinations of methods
will help to improve overall ride. If you have any questions
about ride disturbance and how to improve the ride of
your Motor Grader, please call (800) 905-2367.
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