In the early 50's, demand began to increase for high horsepower wheeled tractors in Europe.
As a quick response, Fiat would sell the model 35-40 from OM (Officine Meccaniche), a company Fiat acquired in 1938. But Fiat knew they would have to develop their own high horsepower wheeled tractor to compete. 
 
Fiat took their existing model 55 crawler tractor, introduced in 1950, and redesigned it to accommodate two axles, wheels, new steering and gearing.
The chassis reminded of the 25R, with the engine, radiator and engine cover resting on two steel beams, connecting the gearbox and differential casing to the front axle. 

On the first models, the engine was started by a small two cylinder petrol powered starter engine.
On the later models 70R and 80R, a 24 volt electric starter motor would become standard.
 
The 55R was launched in 1954, but sales didn't live up to expectations, as a result of many costumers feeling the crawler derived construction was to heavy for 55 horsepower.
 
Fiat responded by increasing the horsepower output to 60 in 1956, but to no effect.
And again in 1958 to 70 horsepower, by increasing the engine speed.
Finally in 1961, they bored out the engine to 6,872cc, thereby increasing horsepower output to 84.

The 84 horsepower would finally satisfy costumers, and the Fiat 80R became, together with the competing Same Ariete, Italy's best selling tractor in its class till 1968.