“In this country, it is not legal for most tractors to travel at speeds above 32 km/h, even if they are equipped with a 50 km/h gearbox.” Basically, the function of brakes is to reduce the kinetic energy of the vehicle by converting it into thermal energy. Depending on the square of the vehicle speed, kinetic energy increases rapidly. For example, a tractor travelling at 50 mph (80 km/h) uses about seven times more energy to brake than a tractor travelling at 20 mph (30 km/h). This situation is exacerbated by the legal requirement that faster vehicles must slow down to higher speeds. For example, tractors at 20 mph (30 km/h) in the past had to be equipped with braking systems that allowed deceleration to 9.3 ft/s2 (2.8 m/s2). When tractors reach speeds of 30 mph (50 km/h), they must slow down to 16.4 ft/s2 (5.0 m/s2), which is consistent with the trucking industry. Q: I was stuck behind a tractor the other day, and it got me thinking about the speed limit for farm vehicles. The North American drawbar hitch is a unique design hitch and may not be suitable for high-speed tractors. The drawbar and tow pin configuration can provide too much flexibility for stable control at higher speeds. A ball hitch (80 mm is considered standard) would be an effective solution, but the position of the ball relative to the rear axle of the tractor is critical. The more the clutch is connected forward, the more stable the towed device is in on-road operation. Unfortunately, moving the attachment point forward reduces the turning radius, which limits operation during field work. According to ANSI/ASAE S430.1, “Tire Load and Pressure for Agricultural Equipment,” farm vehicle tires are not designed for use in on-road vehicles or for speeds greater than 25 mph (40 km/h), with the exception of F1 tires, which are referred to as on-road use.
For agricultural tractor tires, SAE J709 warrants similar designations for travel at higher speeds. American tractors are not traditionally made with suspension systems. However, a fully suspended chassis, i.e. a suspension system for the front and rear axles, can improve handling at all speeds. With a conventional tractor without suspension, weight can detach from the wheels when driving on a bump, resulting in minimal traction when the brakes are applied. The weight is also transferred forward to the front axle, but most of the braking force is located in the rear axle. Together, these factors limit the braking capacity of the conventional tractor. With full suspension, the wheel and axle can get out of the path of rough terrain as the wheels move over bumps on the road, while the weight distribution remains similar. With full suspension, the wheels are more suitable for maintaining contact with the ground, which maximizes the coefficient of traction of the wheels during braking and traction. For example, a complete chassis design allows the machine`s mass to “float” over the entire suspension, while the axles follow the contours of the ground. The weight distribution and bulky rear tires of conventional tractors allowed tractors to generate sufficient braking power with their rear wheels alone; As a rule, these tractors do not have front brakes. The switch to 25 mph (40 km/h) tractors in Europe coincided with the near-universal acceptance of front-wheel drive axles.
This gave manufacturers the ability to activate the front axle drive when braking. This technology has also been adopted in tractor models at 32 mph (50 km/h), with some form of disc brakes built into the front drive system to assist with braking force. Road transport is one of the extreme applications of an agricultural tire, because the worst enemy of a tire apart from the hard skate is heat. The recommended pressure depends not only on the load of the tyre (carried by the axle), but also on the maximum speed. Different load/inflation tables are developed for the maximum speed of the machine. Tire data books list recommended weight capacities and air pressures as well as maximum driving speeds. This led to a debate in the House of Lords and a subsequent 12-month inquiry into the benefits of implementing a subscriber registration and testing system. There have been several strong voices in the conversation – the three main ones being the National Farmers` Union (NFU), the National Association of Agricultural Contractors (NAAC) and the Department of Transportation – so progress has been quite slow.