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 the pneumatic tyres 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.

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 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-tyred 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 aircraft tyres 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.

During those tests, Allis-Chalmers engineers made a crucial discovery. They evaluated the Firestone tires at 70 psi. But those tyres spun out under plowing load in the field. So they experimented by lowering the inflation pressure of the tyres way down to 12 psi. The result was an unqualified success. At the lower pressure, the tyres 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 plough twice as many acres on the same amount of fuel, as well as the ability to travel quickly on metalled roads between fields, made the concept an economic no-brainer.

HME 16 - 1938 Allis Chalmers Model U Tractor