GP Tractor Ahead of its Time

The Massey-Harris GP tractor was a design leader ahead of its time. In The American Tractor, author Randy Leffingwell writes that Massey-Harris engineers took a considerable risk in launching technology of their own design. The GP tractor broke new ground, he says, because “it applied power to all four wheels. It was an attempt to lure farmers away from crawlers or to appeal to farmers who had considered much larger tractors to solve their pulling problems. Massey-Harris’ innovative alternative used equal-size wheels all around.”
Up to that time, four-wheel drive tractors found little success in the marketplace. They were excessively complex and hard to maneuver. Unfortunately, Massey-Harris may have shot itself in the foot with ill-considered promotional efforts. A company brochure said the GP “was designed to actually replace horses in the corn and cotton belt under any soil conditions.” For farmers skeptical about the newfangled technology, those were fighting words.
Farm Implement News, though, was enthusiastic about the new design. In a May 15, 1930, article, the writer identified the GP as the “first really engineered four-wheel drive job that the writer has ever seen. The designers of this tractor had the following requirements in mind: It should be able to operate satisfactorily on any soil or slope where a 4- or 6-horse team can work. It should be adaptable not only to specialized tractor tools but also to the horse tools that the farmer already possesses. It should be light enough to be worked on plowed fields, the soil of which may not be helped by packing, but have enough traction to meet every demand of 2-plow service.
“Then, to get all the theoretical advantages possible in four-wheel drive construction, it was necessary to change radically the normal ratio of weight on front and rear wheels. With rear-wheel drive machines, the static weight on the rear wheels will be approximately 60 percent of the total, with 40 percent in front. This static balance changes the minute the tractor begins pulling so that weight in effect is transferred from the front wheels to the rear. This is particularly noticeable in the case of a light tractor pulling its maximum load, for so little weight may be left on the front wheels that it may be difficult to keep the front end going straight, except straight up.
“With the Massey-Harris general purpose … every ounce of its weight is balanced over its four wheels when a normal load is pulled. … All this translates itself into positive traction, usable not only when surfaces are good and when the lugs can bite, but also in powdery peat and mucilaginous mud.
“In adapting the GP to every variety of horse or tractor tools, the designers approached the problem from two angles. First, they worked out very easy controls, so arranged that extensions to pulled equipment could be easily and quickly made and, when so made, the outfit would be just as responsive as a well-trained team of mules, if not more so.