The advantage of a wheel tractor is the wheels slip, so you have an automatic slip clutch between the tractor and the ground. However, proper air pressures can greatly affect performance in the cut. “You must carry a little higher air pressure on a wheel tractor because of the increased weight,” says Roger Lewno, Case IH team leader of large tractor marketing.
With tracks, performance comes through the powertrain and the engine. Tracks typically perform better in loose underfoot conditions such as sand, while tires perform well in topsoil and clays. Tracks are also better suited for adverse conditions. “The Case IH Quadtrac (track tractor) will get into conditions you simply can’t get into with a self-propelled scraper,” says Lewno.
Tracks offer better ride quality, as well. But it’s important to note that they do come with a little higher operating cost.
While a scraper tractor may have the appearance of an ag tractor, critical differences exist. “The scraper tractor is factory configured to comply with most OSHA requirements,” says Rust. “A customer using an ag version tractor may risk having his/her job shut down because the tractor does not meet or exceed the OSHA requirements to be operated on the construction site.”
Scraper tractor cabs feature ROPS and FOPS. “The seat retainer meets OSHA and MSHA standards, and there is a backup alarm, wide clearance marker, strobe light and external mirror standard to improve jobsite safety,” notes Rust.
The tractors are also built to withstand the tough duty cycle. “In general, a scraper tractor should have a more robust chassis, more appropriate tire and ballast options and more horsepower than an ag tractor,” says Oliver. “Due to the high tongue weight loads of a scraper, scraper tractors should be ballasted heavily on the front in order to deliver the massive engine power to the ground.”
The John Deere Scraper Special features a short drawbar support tongue weight transfer and high-flow hydraulics for fast blade response. The most important feature, however, is the AutoLoad system. “AutoLoad allows push-button loading so that even the greenest of operators can load like a pro,” says Oliver.
Case IH also produces specifically designed scraper tractors that come with the scraper drawbar and a tow cable. “We require the heavy-duty axles with the double reduction compound planetaries,” says Lewno. “We require differential locks on the axles.” It also comes with an upgraded transmission with the default set to second gear on startups as opposed to fourth gear on the ag tractors.
If you purchase a factory produced scraper tractor, most of the configuration/setup has already been completed. “If you’re converting an ag tractor, a common mistake is purchasing a tractor without a powershift transmission,” says Rust. “This limits productivity on longer hauls.”
Proper Weight Transfer
Scraper tractors are engineered to handle the weight transfer from the scraper. “Additional front weights are required to offset the vertical weight transfer the scraper displaces onto the rear of the tractor,” says Rust. “Scraper tractor manufacturers have pre-configured weight packages and tire/wheel configurations.”
Approximately one third of the weight of the scraper is on the drawbar of the tractor. “Say an empty scraper is 18,000 lbs. You have 6,000 lbs. already on the rear of the tractor,” says Lewno. “When it fills, the dirt may weigh about 2,500 lbs. per yard. That weight is transferred to the tail of the tractor.” The nose of the tractor would be weighted to counteract this weight.
When determining ballast requirements, Oliver advises, “Try to achieve an even weight split between front and rear tractor tires under load without exceeding roughly 110 lbs. per horsepower.”
Pull scrapers utilize a special hitch. “A high-strength 1.5-in. horizontal hitch pin couples the tractor to the scraper, which allows the weight to be moved closer to the rear of the tractor,” Rust points out.
The position of the hitch requires special attention. “When hitching a scraper to a tractor, attach it as close to the rear axle and as low to the ground as possible,” says Goossen. “Ideally, the pull point needs to be as close to the center of the tractor as possible.”