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Allis-Chalmers U

Allis-Chalmers’ Model U was not a particularly advanced tractor. Nor did the U make such a huge impact for Allis-Chalmers or on agriculture that it was considered great.

Instead, it was a component of the U – the pneumatic tires – that helped the tractor make history.

Interestingly, the U was not introduced on rubber. Rather, it ran on steel wheels when farmers first saw the tractor. But Harry Merritt, Allis-Chalmers Tractor Division general manager, had a vision of the future of agriculture sans steel runners. Merritt saw great worth in rubber, while other manufacturers shied away from the innovation. Consider that at this same time Oliver was promoting its then advanced Tip-Toe steel wheels on their Model 70.


Merritt was a man of enormous vision. After all, it was he who settled on the Persian Orange color that quickly became an Allis trademark and is still in use by AGCO today.

When he got word of an IHC dealer in Iowa who’d installed truck tires on steel-wheeled Farmalls, a eureka moment ensued, for Merritt knew the time had come to put rubber under his steel-shod horsepower!

Merritt’s acquaintance with Harvey Firestone didn’t hurt in bringing his rubber-tired tractor brainstorm to fruition.

Firestone was intrigued with the possibilities and threw his resources into helping Allis-Chalmers’ engineers test the concept. Soon a pair of 12×48-inch smooth airplane tires showed up at the Allis headquarters. Chief engineer C.E. Frudden found a ready test subject in a Model U owned by a local farmer.

Low pressure key in the field

During those tests, Allis-Chalmers engineers made a crucial discovery. They evaluated the Firestone tires at 70 psi. But those tires spun out under plowing load in the field. So they experimented by lowering the inflation pressure of the tires way down to 12 psi. The result was an unqualified success. At the lower pressure, the tires performed like a dream. Allis engineers discovered that tractive efficiency was greatly enhanced with tires to the point that tractors running on rubber developed over twice as much drawbar horsepower compared to steel.

To plow twice as many acres on the same amount of fuel made the concept an economic no-brainer.

Still, adoption to rubber was not instantaneous. Farmers questioned the durability of rubber compared to steel. And Allis-Chalmers’ competitors attacked the concept, even claiming that dust particles from rubber could poison crops.

Racing tractors

Merritt responded by doing what he did best – promotion. He began holding field demos, pairing a Model U on steel against one on rubber. And to literally drive the point home, he had a fleet of U’s equipped with a high-speed fourth gear, and they raced at tracks across the country. Famed race car drivers like Frank Brisko, Barney Oldfield, and Ab Jenkins performed in front of an estimated 1 million people during 1933 alone. In fact, Brisko set and still holds the top speed record for a tractor at 67.877 mph.

The rest is history. Steel wheels soon littered junkyards across the nation. Pneumatic tractor tires sold like hot cakes. And Harry Merritt would be forever associated with one of the most profound advances in tractor technology.

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