WESTERN PRODUCER — Another instalment in the article series that tracks the development of ag equipment during the 100 years of The Western Producer.
Take a look at images of early tractors and the obvious design differences were wide and varied as inventors searched for that perfect configuration, one that could efficiently turn engine power into usable traction.
Eventually, the standard design we know today became dominant. That is a four-wheeled machine with a driven rear axle. But as engine horsepower grew, that configuration had limitations. So the equal-wheeled, four-wheel drive tractor appeared.
Today, wheels are no longer the automatic go-to for engineers. Rubber belts are quickly becoming dominant in very-high horsepower applications.
Where the concept for the rubber belt originated is an interesting story.
Through to the 1970s, the steel-tracked crawler had remained popular with farmers in some regions because of its unbeatable traction. Caterpillar, the company that dominated the crawler market in North America, eventually focused primarily on the construction sector, designing its crawlers to push a blade. But because of continued interest from farmers in some regions, the company continued to build some specialty machines, dubbed “SA” models. (SA stood for special applications.) They were introduced in 1966 and built for pulling implements.
But the SA models had drawbacks. Steel-tracked machines were slow, couldn’t be driven on roads and compared to the evolving high-horsepower ag tractors popping up through the 1970s, they were underpowered and heavy.
With new contenders in the construction equipment sector from Japan and Europe setting up shop in North America, the sales picture for Cat slowed considerably in the 1970s, so the company looked for ways to sell machines into sectors outside of construction. Company executives turned their attention to agriculture and how they might attract more interest from farmers for the SA crawlers.
At the same time, the rubber products division Cat owned, which had built high-pressure hoses and large tires, was sold to Goodyear; but Cat retained its rubber materials production equipment. Earlier, engineers had designed a very large mining equipment tire with a removable/replaceable tread, which had about the same dimensions as a steel track. The company explored the possibility of using that tread as a rubber track.
Road graders were the first machines they were tested on. It was a natural fit, because the graders have fixed tandem drive axles. Initial tests were successful. The belts proved to be quiet, smooth and could run fast on paved roads. They also reduced the loping effect of wheeled machines at high speeds.
Eventually, the rear portion of a grader was used as a test mule to evaluate the pulling performance of rubber belts, which proved to be almost as good as steel tracks.
While engineers tried the rubber belts on several Cat machines, the engineer working on improving the SA crawlers, Dave Janzen, and the engineer working on the rubber belt testing, Ron Satzler, got together and create a rubber-belted SA designed to pull farm implements.
I interviewed them years ago about how their collaboration was eventually a key part in the creation of the first belted Challenger 65, which was released in 1987, after nine years of development.
First, the SA design needed to be improved. The centre of gravity needed to be moved forward on the tracks to improve its pulling ability, with a 50-50 weight distribution on both axles. It needed a steering wheel instead of brake levers as well as a suspension, and it needed a higher horsepower-to-weight ratio. That meant more power to compete with high-horsepower ag tractors.
The project swung into high gear in 1979.
The result was the creation of the “Red D4 BAT”, which became the original Challenger prototype. It was a modified D4 crawler with rubber belts and reconfigured to meet all of those engineering criteria, including using the relatively new differential steering system. That allowed it to steer like a regular machine, not “jerk steer” like a conventional crawler. And it kept power flowing to both tracks in a turn, unlike most regular crawlers.
Also important to the company was keeping the project a secret.
The Red D4 BAT’s name came from the fact it was painted red to look like a Versatile tractor to anyone seeing it at a distance, camouflaging it. BAT stood for “belted ag tractor.”
At the same time the Red D4 BAT was undergoing testing, Cat had another ag tractor project in development: a conventional four-wheel drive tractor. But development funds were tight. Funding both ag tractor developments was out of the question. Eventually, management decided one of the projects would have to be scrapped.
The story among Cat engineers was the company’s engineering vice-president and several of his senior executives made a trip out to the farm where the Red D4 BAT was pulling a nine-furrow plow to see it in action. They were impressed.
On the 80-kilometre trip back to their offices, it was decided Cat was a tracked-machine company, and if only one ag tractor project was to make it to production, it ought to be the belted design. The next day, the four-wheel drive project was cancelled, even though it was near to being ready for production and the company had already invested in some tooling to produce it, to the astonishment of its design team.
The belted Mobil-trac concept had won out.
A number of tests were conducted to determine the effect of belts on soil. Cat’s data showed a reduction in compaction and a double-digit increase in crop yields in those locations. Despite that, Satzler said after Challengers went into production, getting people to listen to the compaction advantages early on wasn’t easy, and it frustrated the company.
During the four-wheel drive project’s development, the senior industrial designer had worked for General Motors before coming to Cat and created an automotive-style appearance with a sloped-hood appearance on the wheeled tractor. That would eventually be carried over to the belted tractor as it entered the pre-production stage of development.
Notably, the sloped windshield it used was common in automotive applications but uncommon in ag equipment. The prevailing wisdom of the day was too much dust would stick to the slanted glass and cause a problem. Some brands’ cabs at the time actually used a reverse slant to avoid this perceived problem. In field trials, though, it proved not to be a problem at all.
Cat also had to pay particular attention to the cab interior. Making it a comfortable environment is something that wasn’t a priority in the previous SA crawlers or in any of Cat’s construction machines, which would be mostly operated by owners’ employees.
Ag tractors, on the other hand, were typically operated by their owners who wanted comfort. So the belted Challenger would get the most comfortable cab Cat had ever built.
Just before the Challenger tractor was officially unveiled to farmers, the space shuttle Challenger disaster occurred. Management at Cat was briefly concerned about their choice of names, thinking it might evoke negative emotions based on the space craft’s destruction. But they stuck to it and in the end there were no significant marketing problems.
In 2002, Cat sold the Challenger line to Agco, which is now the basis for the Fendt MT 900 and MT 1100 tractor Series.
