Equipment Type

Wheelbase Is Key to Skid-Steer Productivity

While almost anybody can make skid-steer loaders move fast, they require finesse and a sense of balance to finish jobs smoothly

December 01, 2005

 

Match Finishing Passes
Match Finishing Passes
A skid-steer loader's bucket is only as level as its tires, so finish grading has to start on a flat surface. Iron out a starting point by shaving the high spots and filling the lows in short pushes. Work with the loader arms down and the bucket flat, using minor corrections in bucket angle to vary the depth of cut. Slow ground speeds and fast engine rpm give the operator time to react and the hydraulic system power to respond. Use a method called "pass matching." Once you've carved a level pass, make cuts half a bucket wide, using the other half of the bucket as a depth gauge following the existing grade.
Weight Distributed on Short Wheelbase
Weight Distributed on Short Wheelbase
Design features that make skid-steers fast and nimble can also present stability issues. In order to steer around one axle, the machines carry 60 to 70 percent of their weight on the rear axle. When loaded, most of the gross weight rides on the front axle. Wheelbase is only 45 inches on the average machine with 2,200 pounds of rated operating capacity. Jackrabbit accelerations with no load in the bucket can raise the front wheels off the ground. With a tread width of just 56 inches, these machines can tip to the side if the operator doesn't manage the center of gravity by controlling the speed and load height.
Wear the Seat Belt
Wear the Seat Belt
Use the safety bar and wear safety glasses, a hardhat and steel-toed shoes.
Source: AEM
No Riders
No Riders
And never move or swing a load over anybody's head.
Source: AEM
Stay Inside
Stay Inside
Never enter or leave the operator's station when the loader arms are raised.
Source: AEM
Three Points of Contact
Three Points of Contact
When you mount and dismount, keep three points of contact with the machine — both hands and one foot, or one hand and both feet.
Source: AEM
Heavy End Uphill
Heavy End Uphill
Travel up and down steep slopes and ramps with the heavy end of the machine pointed uphill. If the bucket is empty, that requires backing up the hill. With a full bucket or a heavy attachment, it requires backing down the hill. Do not drive across steep slopes. If you must travel on a slope, and it is not excessively steep, keep the load low and proceed with extreme caution.
Radius vs. Vertical Lift
Radius vs. Vertical Lift
Skid-steers with vertical-lift loader mechanisms are best for forklift work, and they can excel at loading trucks because they reach farther than radius-lift machines at the top of the lift range. The linkage also holds the forks or bucket closer to horizontal through the entire lift path. Simple radius-lift machines are typically better for digging and using heavy work tools because a system with fewer moving parts generally withstands stress better with less maintenance.

 

Design elements that make skid-steer loaders indispensable on most jobsites can also present some challenges to productive operation. With hydrostatic drive on a short wheelbase and narrow tread width, the skid-steer is fast and maneuverable. Unpracticed or careless operators will occasionally struggle to keep all four tires on the ground.

"The machine is deliberately unbalanced, with 70 percent of its weight over the rear two wheels when unloaded and 70 percent of the gross weight over the front two wheels when loaded," says Glenn Lee, safety and training manager with Bobcat Enterprises, an equipment dealer in Cincinnati. "It has to be designed that way to turn efficiently.

"Most people don't realize the degree of the disparity in weight, or how easily the machine can be tipped back," he adds. "It will do a wheelie if you push sticks forward too quickly, but you don't want the machine bouncing around the jobsite."

Lee observes that, because the machine is small, rushed operators sometimes fail to respect the fact that they're moving as much as 3,000 pounds of material.

"We have to stress that operators move the sticks smoothly and operate the skid-steer controllably," says Al Weishaar, skid-steer loader product specialist at Caterpillar. "It's more of a problem with less-experienced operators. Their impression is that if the machine is moving fast, they're getting production. But that's not necessarily the case."

Weishaar strives to refocus attention on handling material one time, or as little as possible, and properly applying the work tool.

"Try to use the full capacity on every load," he says. "That's how real production can overcome the image of speed as production.

"Excessive speed could cause damage to the machine or injury to the operator if they're working in really rough conditions," Weishaar adds. "I have seen skid-steer loaders going so fast over rough surfaces that the tires are leaving the ground. The machine and operator will both survive longer if they slow down."

A skid-steer's hydrostatic drives react very quickly to movement of the control levers. All trainers advise skid-steer operators to check their path before turning or reversing the machine.

"A skid-steer loader very quickly can change direction in any way — almost instantly," says Weishaar. "There are a lot of visibility issues, especially to the rear and rear sides.

"With your daily inspection, make sure the travel or backup alarm is working," he adds. "We've incorporated rear-view mirrors, which decreases turning around to look behind you, but still doesn't take away all your blind spots."

A training videotape from VISTA called Skid Steer: Safe Operating Techniques suggests, "If anybody walks up to the machine to talk to you, put the loader arms down and turn the machine off. Don't restart until the area is clear."

Filling a skid-steer's bucket is much like getting a full bucket with a wheel loader. Drop the bucket flat on the loading floor and drive into the bank or pile until you lose power or traction.

"Then raise the loader arms slightly to plant all the tires firmly on the ground," says Weishaar. "Curl the bucket back until it's full. You may not get the complete fill factor when digging muddy ground, but rated load is based partly on material density. You can reach the rated operating capacity of the bucket and the machine even if you don't get the bucket completely full."

A skid-steer loader can pick up more than its rated operating load. Skid-steers are rated to work with only 50 percent of their tipping capacity because when they put a load in motion, the dynamic forces on a short wheelbase and narrow tread width can tip the machine.

"Loading from a pile, some persons will gouge into the pile instead of scooping," says Marty Turek, curriculum developer and instructor with the Operating Engineers Local 150 in northern Illinois. "They push in and roll the bucket to get a load in a snap, but stickier materials won't want to come out of the bucket. For the sticky materials, you have to make more of a linear cut — penetrate and then raise the loader arms, making a shallower, longer cut upwards."

Roll the bucket back as it fills to keep the load in the bucket.

"We see these machines building a ramp in front of pile, too," says Turek. "When they come up to the pile they don't have enough down pressure on the bucket, or the bucket's not flat on the ground. You might even want a slight downward angle to make sure the bucket is cutting when you get to the pile."

The loading floor has a significant impact on the unsprung skid-steer loader's productivity and the operator's endurance. Turek recommends keeping the bucket down on the ground most of the time in a loading area, always working to keep it smooth.

"You'll see cowboys who like to bring the front two wheels up off the ground as they're driving into the pile. They think they're getting more down pressure, but they're actually giving up half the machine's traction and increasing down pressure on the rear tires. Those rear tires dig ruts in the site, which decreases traction on later passes," says Turek. "It doesn't really matter if the tires are up or down. Physics say you only have so much weight on the machine, so you're only going to get so much down pressure. If you want more penetration, just tilt the bucket angle down a little more."

"To achieve breakout force, start with the bucket flat on the ground and raise the lift arms slightly, then use bucket angle to penetrate hard material,' says Caterpillar's Weishaar. "Keep all the tires on the ground and planted firmly. Then it's easy to make changes in the penetration force with minor changes in the bucket angle."

"The short wheelbase makes finish grading more difficult," says Turek. "If you have one tire that's not level with the others, the bucket has to tilt. Since the tires determine the pitch of your bucket, you have to level the area where your tires are sitting.

"Start shaving down the high points," Turek recommends. "If you're not comfortable, take a ½ of a tenth at a time. It's hard to do, but if you take a few minutes to set up, it will make the rest of the job a lot easier.

"As soon as the bucket gets out of level, stop and back up. If you keep going, you'll make it worse because the bucket goes up when the front wheels go over a hump and when your rear tires go up the bucket cuts down. It just facilitates cutting a wave pattern into the surface."

Once the starting point is leveled, you can work outward from that point using a method that Weishaar calls "pass matching."

"If you want to maintain an established grade, you start from a level point and make passes half a bucket wide, matching each pass to the existing grade," says Weishaar.

"Work with the bucket flat, the loader arms lowered, and use minor corrections in the bucket angle to vary the depth of cut. A little correction in the bucket angle is easier and faster than correcting using the loader arms.

"The key to finish grading with a skid-steer loader is slow travel speed and high engine rpm," he adds. "At low engine speed, the hydraulics will be too slow to respond. At high travel speed, it's hard for the operator to respond quickly enough. It's another one of those situations where going fast is not always the most productive choice."

Weishaar warns finish graders to limit their bucket loads and avoid wheel slip. Spinning causes unnecessary tire wear and requires grade rework.

"If you're not fine grading but smoothing a work area you can leave some contour there, but you definitely want to be level at the point of high lift or loading into a truck," says Weishaar. "An uneven load in the bucket can really compound a slight side slope and risk tipping the loader. A slope down to the truck can decrease the loader's rated operating capacity dramatically."

Carry loads as low as possible to keep the center of gravity low and to leave an unobstructed view from the operator's seat.

Drive straight up and down slopes. The heavy end of the machine should always be uphill. With most of the machine weight on the rear tires, an unloaded skid-steer should be backed up slopes. When the loader is carrying its rated capacity it can be driven forward up slopes, but should be backed down.

Slow down when approaching to load a truck or hopper. Drive as close to the dumpsite as possible and raise the bucket slowly.

"Travel as little as possible," says Weishaar. "You could get dynamic tipping caused by hard braking and hoisting at the same time. It compounds the weight transfer forward."

When raising the bucket, be careful to keep it level. A very full load can spill over the back of the bucket, into the operator's compartment, and onto the operator's feet.

Loaders with vertical-lift linkage are designed to hold the bucket or pallet forks more nearly level. And because they do not swing the load upward in an arc as a radius-lift machine does, there's less demand to roll forward with arms in the air to place a load.

VISTA's Safe Operating Techniques video bridges from this point to remind operators to wear proper protective gear. "Wear safety glasses. If a rock tumbles off the back of the bucket and shatters the windshield, you're going to need eye protection."

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