In 1958, Zetor introduced it's first unified range. This meant that each tractor used common components, but ended up ranging in size, power and features. Over one million UR1 Zetor Tractors were produced.
The Zetor 3011 was the first tractor to be produced in UR1. The 3011 had a power rating of 37hp at 2200rpm. It had a modern direct injection diesel engine, which was very advanced for the time. The tractor had ten forward speeds and two reverse speeds, with five of the speeds between 2.5mph and 7.5mph, the most common speeds for field work.
Other models at the same time included the 2011, a less powerful version of the 3011. Specialist models included the 3016 and 4016, half tracked versions for use in snow and weak soil, the 3017, with a lowered centre of gravity, and the 2023, a narrow fully tracked version. Also, there was a 3045, which had 4WD (although the front wheels were only driven in "High box". Finally, there were the 2013 and the 3013, which were narrow orchard tractors..
In 1966, a more robust and powerful model above the 4011 was produced, the Zetor 5511. In 1968, positive feedback from customers prompted the Zetor Engineers to update all "0" models to the "5" series - 3011 became 3511. The bonnets of these more modern tractors were square instead of rounded, and the tractor looked a lot more robust than it's predecessor.
Again, in 1972, the tractors were upgraded. A review of the UR1 models was carried out, and on the agenda was more load carrying capacity and traction. The engines were stronger, the tractor was heavier and the front axle sported stronger hubs.
The 5711 and 6711 had an optional extra of a torque multiplier, which doubled the number of speeds. If you applied the torque multiplier, your torque increased 23% whilst your speed decreased by 23%. When this option was fitted, there were 20 forward and 4 reverse speeds.