Slope Coping: Tracks vs. Wheels

One example of Italian engineering excellence is the narrow tractors with same-diameter wheels increasingly used as an effective alternative to tracked models adopted where the slopes get steep. Mixed tracked/wheeled models are the latest development

About 42% of Italy is classified as hilly, and 35% as mountainous. Most of the urban areas and the major infrastructures are in the plains so it follows that farming is often pursued in the hills or mountains. This fact in itself has important consequences for agricultural engineering, and this is all the more the case when one remembers that Italy’s most important crops come in large part from orchards and vineyards, where planting patterns often leave little space between rows and require the use of machinery usable in narrow spaces. Tractors have to be narrower, often much narrower, giving easier handling in the available space, especially in the turning areas at the row ends.

As the topographical facts suggest, it is no coincidence if specialised tracked tractors were increasingly popular in 1970s Italy because they undoubtedly offered greater stability, with a lower centre of gravity, most of the weight over the front axle and a very broad area of contact with the ground.  But this section of the market has in recent decades gradually converted to tractors with ‘iso-diametric’ wheels – wheels having the same diameter.

Their main characteristic is the engine mounted jutting in front of the front axle, typically putting 60% of the weight at the front and 40% to the rear. Since the centre of gravity is also low, they can replace tracked models wherever the slope is slightly or medium sharp. But they are also enormously more mobile off the slope since they can reach the legal limit of 40 km/h on the highway, compared to the tracked models’ 15 km/h. Comfort, especially for vibration, is also significantly superior. Tracked tractors remain as part of the market mix because they are still irreplaceable for very steep terrain.

 A Little History

Same-diameter wheels are certainly not the latest discovery in technology. Even if larger, the first Italian model with this design was probably the Pavesi P4, which appeared soon after WWI and had 4WD and a front and back chassis resting on a single tubular strut and linked by a central joint. Today, this design approach still ensures high traction even when the ground is very uneven since it can follow the surface’s pits and peaks, both lengthwise and crosswise, maintaining continual wheel contact with the ground.

At the end of the 1950s, Pasquali produced the first same-diameter specialist tractor – a small petrol-powered model with 4WD and steering on the central link.  The machine was a success and was soon made available in a larger version with a more powerful diesel engine and larger tyres. Inevitably, it was less easy to handle so, in 1974, Pasquali introduced a series of specialised tractors whose front wheels were slightly smaller than the rear ones. This made it possible to reduce the steering circle even more and to win back manoeuvrability. As a technical solution, the idea was spot on and was taken up by other manufacturers making narrow gauge specialised tractors.  

 Steering Solutions

Tractors with same-diameter wheels have adopted various approaches to the small steering radius needed to ensure great ease of handling.  The simplest is a central, hydraulically controlled joint linking the two halves centred on the front and rear axles respectively.  Steering radius is very small and the rear wheels cover the same tracks as the front ones, which reduces wide soil compaction, but deepens the compaction at the points where it occurs. On the other hand, the driving seat is cramped when turning, and stability is reduced when turning on a slope.

One alternative is classical front-wheel steering, which certainly ensures greater stability. But some manufacturers, for example BCS (also for the Pasquali and Ferrari makes) and Pierre Trattori sell machines with both types of steering, achieving a very small turning radius. Pierre has also introduced the interesting idea of improving stability on slopes by making the central joint more rigid.

 Reversing the Cab

For maximum versatility, a 180° switch in the direction the driving seat is facing is a fundamental peculiarity of this class of tractors. On iso-diametrical tractors, the switch is made thanks to a pivot on which the driving seat can spin around along with all the main controls.

Even though guaranteeing stability on hilly terrain, it’s worth remembering that the typical distribution of weight on a tractor with same-diameter wheels could create problems if the tractor has no load and has to brake very quickly on the highway. This is because the rear end is significantly lighter. Given the short distance typically found between the axles, driving in the higher gears on the highway is relatively uncomfortable. The situation improves if a tool is attached to the rear three-point hitch since this provides better balance.

 Rubber Tracks vs. Tyres

Kubota of Japan was the first manufacturer to introduce a rubber track in place of the two rear wheels. Applied to a traditionally configured tractor, the idea was to improve traction by increasing the area of contact with the ground.  In this connection, Antonio Carraro’s Mach 4 narrow model has four rubber tracks in place of wheels. In effect, these give much the same on-field performance as a classical tracked tractor, but with great agility and speed on the highway. Recent intermediate solutions include BCS’s SkyJump with its rear rubber tracks and double steering system on both the central articulation and the front wheels. 

In fact, tractors with iso-diametric wheels are a very Italian passion supported by the major manufacturers such as Antonio Carraro, BCS, Goldoni and the ARGO Group, especially with its Valpadana models.  They have recently been joined by SAME Deutz-Fahr and New Holland thanks to commercial agreements with Antonio Carraro for the former and Goldoni for the latter, bringing them into a very lively niche market whose characteristic is a wide range of technical solutions and variations on the theme, to give an effective answer to the requirements of specialised crops in Italy.