Spec Sheet: Motor graders

Editor’s note: Spec Master delves deeper into the specifications reported in our annual Equipment World Spec Guide. This month’s guest expert: Dan Gillen, product support manager for motor graders, Caterpillar.

Frame type (rigid or articulated)
Articulated motor graders make up the vast majority of machines today – in fact, according to the Equipment World Spec Guide, there are only three rigid frame machines sold in North America. Be aware, however, the articulation joint can be put in one of two positions: in front of the cab and behind the cab. (Caterpillar is a proponent of the behind-the-cab articulation joint position, citing better visibility to the moldboard.)

Operating weight (lbs)
Since weight is a determiner in machine sizes, it tends to be a premier spec in buyers’ minds. But the important aspect of weight is how it’s split on the machine – how much weight is on the rear axle and how much is on the front axle. Typically, about 70 percent of a machine’s weight is on the rear, which gives the machine power and traction; and 30 percent of the weight is on the front axle, which gives the machine control. Be aware of the fine print on this spec – some spec sheets will include the weight of attachments with the base weight, saying the machine is “typically equipped” with these attachments.

Make sure you know if the machine gives you the ability to take advantage of the full moldboard length. Some machines have a fixed-position moldboard, so the moldboard slides left or right from a fixed point. Others have a three-position moldboard anchor that can further extend the machine’s reach left or right. A smaller-length moldboard that has the ability to change anchor positions may have more right-left reach than a fixed-position moldboard that’s a bit longer.

Moldboard height (inches)
Combined with moldboard length, this is an indicator of how much material you can carry. Caterpillar says you should also look at throat clearance – this is the distance from the top of moldboard to the bottom of the circle when the moldboard is tipped all the way back. Throat clearance becomes important as the material you’re carrying rolls across the moldboard. If you don’t have adequate throat clearance, that material will strike the circle and fall down to be reprocessed, leading to inefficiencies in productivity and fuel burn. If you put a taller moldboard on a grader, you need to be aware it will reduce your throat clearance.

Moldboard thickness (inches)
This is not a major spec, since manufacturers in the North American grader market typically have a moldboard that is 0.78 to 0.98 inches thick.

Blade lift above ground (inches)
Typically you would only consider this spec when you don’t want the blade to come in contact with any material while the machine is moving. The blade, however, will always be able to lift higher than the lowest point of a grader (usually a transmission or front axle), so your high center point is typically lower than the moldboard cutting edge.

Maximum blade side shift, right/left (inches)
This is an important spec, especially for those who consistently use graders to ditch or slope. As discussed under “moldboard length,” some machines have a fixed side-shift anchor and on other machines you can change the side-shift anchor position and further extend the machine’s side reach.

Shoulder reach, frame straight, right/left (feet/inches)
The shoulder reach tells you how far you can reach your blade out right and left with the frame of the machine straight. Shoulder reach is different from side shift in that the operator is also incorporating the drawbar center shift feature of the machine, which uses a separate cylinder under the front frame. Side shift only uses the side shift cylinder, which is mounted to the moldboard.

Net engine horsepower, first gear
Because it’s an indication of a machine’s production potential, this is one of the first specs people typically consider. It can be misleading, however, since most motor graders are traction-limited in first gear, with more available horsepower than the machine can use.

Maximum variable power, net
This is another spec that’s popular in machine comparisons. Most manufacturers offer variable horsepower machines, with horsepower limited by what gear you are in – the higher the gear, the higher the available horsepower.

Torque rise (percentage)
Although this is a long-standing spec, Caterpillar maintains it has little meaning. This spec represents the increase in engine torque as the engine is put under increasingly heavy load, from high idle to maximum lug. Torque rise, however, can be changed just by changing the rated speed. Torque curve charts and the peak torque numbers will give you more information on machine performance.

Number of gear speeds, forward/reverse
This is an important spec because you want to be able to match a gear to your application, so the more gears available, the easier this is to do and run a machine at its “sweet spot.” For example, if you want to carry a heavy load at 3 mph, this application will require getting the most torque out of the engine, perhaps running it at 1,500 rpms. If you’re required to run at full throttle to go 3 mph, then your machine is burning a lot of fuel and you’re not maximizing your engine. It’s important to have a number of gear choices: Most manufacturers have eight forward gears in the most popular motor grader sizes. The number of gear choices is not as important when going in reverse, since the machine is not moving material.

Maximum speed, forward/reverse (mph)
This spec comes into play when roading your machine, since higher speeds will get you to the job faster and help productivity. This is also true with the reverse maximum speed. If, for instance, you’re working at a building pad where all of your work is done in one direction, you’ll want to have a comparatively fast reverse speed.

Standard tires
Motor grader manufacturers work closely with tire manufacturers to get the right standard tire match for their machines. But you also might want to check out the available tire options made possible by recent advances in tire technology. These include snow tires that eliminate the need for chains, radials and wide-based tires that offer better flotation for work in sloppy areas.

Front- or all-wheel drive?
All-wheel drive can improve the performance of a machine in certain situations – especially if you need more control of your front wheels and steering or if you’re working in snow and ice. Because it’s a more complex design with an additional hydraulic pump and set of drive motors, it’s more costly to operate and maintain. Be aware that it’s not necessarily true you’ll have more power or rimpull with an all-wheel drive grader. While you might have a higher traction coefficient, unless you’re traction limited, all-wheel drive doesn’t necessarily make a machine more productive.

Front axle oscillation (degree)
An important but overlooked spec, this tells you how much the front axle can oscillate back and forth before it hits the frame stops. Oscillation allows the machine to travel over uneven surfaces without affecting the frame, so the operator doesn’t have to make a moldboard adjustment. You’ll be more efficient if you can oscillate over most obstacles without affecting the frame or blade.

Front wheel steering angle (degree)
This measures how sharply you can turn front wheels.

Minimum turning radius (feet/inches)
This gives you an indication of the machine’s maneuverability, and whether or not it has the ability to turn around in the width of the road without doing a three-point turnaround. There are two ways to look at turning radius: with the frame straight and with the frame fully articulated and wheels fully turned. The measurement most indicative is the one taken fully articulated and leaned because that’s the position a machine should be in during a turnaround.

Wheel base (feet/inches) (Point A on illustration)
This is the measurement from the centerline of the front axle to the centerline midway between the rear tandem axles.

Overall length, width over tires and height to top of cab (feet/inches) (Points B, C and D on illustration)
All of these dimensions affect transportability. Overall length combined with wheel base will also affect a machine’s minimum turning radius.

Caterpillar would add:
Blade base (feet, inches)
The distance between the center line of the front tire and the center line of the first rear tandem tire is the distance carry material before the blade interferes with the tire. If you rotate your moldboard too far forward, you’ll hit the front tire, and if you rotate it too far backward, you’ll hit the rear tire.

Moldboard heel clearance
To measure this, take the moldboard and put it at a 90-degree angle, perpendicular to the ground. Then measure how far you can get the moldboard heel away from the ground. Keeping the heel of the moldboard in line with the outside of the tandemtires will give enough heel clearance to allow operators to reach higher up a slope and clean more material out of the ditch.

WHEEL LEAN (degree)
Motor graders have a feature called wheel lean. Operators lean their wheels for a number of reasons, including counteracting side drafting when processing material so the machine will track straight. While it depends on the geometry of the front axle how much the axle will oscillate when you lean your wheels, it’s typically about 15 degrees. Some machines can lose almost all their axle oscillation when they lean their wheels, so oscillation can be significantly affected by wheel lean. According to Caterpillar, this impact is easy to measure: Fully lean the wheels on a machine and put an angleometer (you can buy them at a store such as Sears) on the front axle and measure how much oscillation angle is left when the wheels are fully leaned. For example, if the angle is zero when the wheels are straight and goes to 8 degrees when the wheels are fully leaned there are about 7 degrees of oscillation left.