What Size Slasher Do You Need for Your Tractor?

As a starting point, budget roughly 20 to 25 kW of tractor power per metre of slasher width for general grass, and more for dense or woody material. On that basis a 45 kW (60 hp) tractor comfortably runs a 1.8 m slasher in normal conditions.

That is the rule of thumb. The rest of this article is about when it does not apply.

The sizing table

| Cutting width | Tractor power | Typical use | |---|---|---| | 1.2 m | 18–26 kW (25–35 hp) | Compact tractors, orchards, smallholdings | | 1.5 m | 26–34 kW (35–45 hp) | General farm work | | 1.8 m | 34–45 kW (45–60 hp) | The most common size sold | | 2.1 m | 45–60 kW (60–80 hp) | Larger areas, contract work | | 2.4 m+ | 60 kW+ (80 hp+) | Open ground, high output |

Manufacturer specification for the specific machine always overrides a general table. Machines of the same width differ in deck weight and gearbox rating, and both change the power requirement.

Three checks, not one

Power is the check everyone does. The other two get skipped and cause just as many problems.

1. PTO power

Note that tractor power is usually quoted at the engine, while what matters here is what reaches the PTO — typically around 10 to 15 percent less. If your tractor is quoted at 45 kW at the engine, plan around roughly 38 to 40 kW at the shaft.

Also confirm the PTO speed. Most slashers in this class are built for 540 rpm. Fitting a 540 rpm implement to a tractor running 1000 rpm will destroy it quickly.

2. Lift capacity

Your three point hitch has to lift the machine, and a slasher is heavier than it looks — a 1.8 m machine commonly runs 300 to 450 kg depending on build. Lift capacity is quoted at the ball ends, and it drops significantly further back. A slasher's weight sits well behind the hitch, so a tractor with a quoted 1,500 kg lift may have considerably less available for this implement.

If the tractor struggles to lift the machine clear at headlands, you are over the limit regardless of what the power figures say.

3. Stability and ballast

Hanging 400 kg off the back of a light tractor unloads the front axle. That costs you steering, and on slopes it is a safety problem, not a comfort one. Front weights or loaded front tyres solve it. If you cannot get the front end planted, the machine is too big for that tractor.

What pushes the requirement up

The table assumes ordinary standing grass on reasonably level ground. Each of these moves you toward a smaller machine, or a bigger tractor:

• Dense or woody material. Bush, thick reeds and old rank growth can double the power draw compared with grass.
• Slopes. Climbing while cutting takes power away from the PTO.
• Tall material. Anything you have to cut in two passes is telling you the machine is working hard.
• Sandy or soft ground. Rolling resistance eats power before the blades see any of it.
• High altitude. Naturally aspirated engines lose output as altitude increases — relevant across most of the Highveld.

What lets you go wider

• Short, light regrowth
• Flat, firm ground
• A tractor with plenty of weight and a comfortable margin on lift capacity
• Slower ground speed and patience

Why oversizing is worse than undersizing

An undersized slasher costs you time. You do more passes than you would like and the job takes longer.

An oversized slasher costs you money. The symptoms follow a predictable order: you drop ground speed to cope, then the cut quality falls off because you are running the PTO below rated speed, then the gearbox runs hot, then seals go, then bearings. The machine that looked like better value ends up as a repair bill and a tractor with a worn driveline.

If you are between two sizes, take the smaller one. You can always cut faster. You cannot un-cook a gearbox.

Two worked examples

A 38 kW (50 hp) tractor cutting camp grass on flat ground. Engine power is 38 kW, so allow about 33 kW at the PTO. That comfortably supports a 1.5 m machine and will handle a 1.8 m in easy conditions. If the camps have any real bush in them, take the 1.5 m.

A 60 kW (80 hp) tractor doing contract firebreaks on mixed terrain. Roughly 52 kW at the PTO. A 2.1 m machine suits the power, but firebreak work often means thick material and uneven ground — a 1.8 m machine run properly will likely finish the day sooner and with less strain.

Quick checklist before you order

• Tractor make, model and rated power
• PTO speed: 540 or 1000 rpm
• Three point hitch category: Cat 1, 2 or 3
• Lift capacity, and whether you have front ballast available
• What you actually cut, honestly — grass, or bush
• Terrain: flat, undulating or steep

Send us your tractor model and what you are cutting, and we will tell you which size fits — including when the answer is that you need a smaller machine than you were planning to buy.