Don’t be baffled by tractor techno-speak

Finally thinking of investing in a new tractor after a long period of patching up and making do? Baffled by the salesman’s techno-speak, though? Andrew Pearce explains what some of this grand-sounding terminology actually means.

The march of progress brings many things, some welcome and some not. For most people, the constant drizzle of techno-speak that goes with technological progress definitely falls into the latter category.

We’re talking here about all those clumps of letters and whizzo-sounding terms which salesmen wave around at buying time, whether you’re after a new tea cosy or a new tractor.

The trouble is, it does (rather sadly) make sense to know what all this stuff means. Partly to avoid feeling dumb when the salesman is in full flow, but mainly to avoid paying for stuff you don’t actually need. Or to avoid missing out on some feature that really would make life easier or cheaper.

So here’s a guide to some of the more common puzzlers, stitched together with the tractor buyer in mind. Feel justifiably smug if you know all that follows become a better bluffer if you don’t.

(1) Tier 3 (or Stage 3) engine

tier 3 engine

An engine certified to meet the current limits for emissions of particulates (tiny bits of soot and other diesel by-products) and oxides of nitrogen. All engines on new tractors should have it. Stricter Tier/Stage 4 limits arrive here on 1st January 2011.

What’s good about it? Cleaner air for all.

What’s bad about it? Meeting Tier 3 calls for (among other things) very high-pressure fuel injection with electronic control, adding expense and further limiting scope for on-farm repair. Tier 3 compliance usually brings heavier fuel consumption compared with an equivalent Tier 2 engine.

(2) Exhaust Gas Recirculation (EGR)

Exhaust tractor

A way to cut emissions by feeding cooled exhaust gas back into the engine. The recirculated gas – mainly carbon dioxide and water – soaks up heat, lowering combustion temperature and decreasing the formation of oxides of nitrogen (see 1).

What’s good about it? Cleaner air for all

What’s bad about it? EGR in diesel engines decreases power and increases particulate (soot) emissions. Tractors may need a particulate filter (soot trap) to meet future emission standards, increasing cost and complexity while potentially further increasing fuel consumption.

(3) Good torque backup

torque diagram

Torque backup is the rise in engine twisting force (torque) which happens as engine revs fall away under increased load. Power = torque x revs, so if revs drop, so does power unless torque climbs to compensate. The driver of a tractor with good torque backup will feel the engine still fighting as a heavy load forces revs to fall.

Old-style engines show a relatively gentle rise in torque, so power always drops with rpm. Today’s constant-power engines show a much steeper rise in torque, particularly just below maximum revs. As a result, power stays steady over a limited band and the engine can better shrug off variations in load.

What’s good about it? Strong torque backup limits the drop in forward speed as load goes up, and lets you hold on to a gear for longer.

What’s bad about it? Nothing.

(4) Power rating


Tractor engine powers have to be rated according to some standard so the buyer knows what’s on offer. But there isn’t a universal standard. So one engine can have several different power ratings, all equally valid, depending on measurement conditions.

Common standards are ISO/TR 14396, EC 97/68 and ECE-R24. Of these, ISO is the most internationally-accepted. Older standards are DIN 700200, BS AU 141, SAE J1349 and SAE J1995. All refer to power at the engine crank, not at the tractor’s pto.

Standards differ in what’s connected to the engine during the test (alternator, fan, etc), the ambient conditions and perhaps fuel density. Conversion between standards can be tricky, although power quoted to ISO/TR 14396 is much the same as power according to EC 97/68. Consequently, compare only like with like when looking at tractor spec sheets, ie ISO power with ISO power, and so on.

What’s good about it? Gives potential for useful comparison.

What’s bad about it? Scope for confusion if like is not compared with like.

(5) Turbocharger plus intercooler


An engine is essentially an air pump. The more air you can move through it, the more fuel it can burn and the more power it will produce.

A good way to cram more air into an engine is to compress it, and one way to do that is to use a turbocharger. This is just a shaft with a vaned wheel at both ends, held in a housing. One vane is blown round like a windmill by hot exhaust gas, letting the other end compress filtered air, which then goes to the cylinders. A wastegate limits pressure (boost).

But compressing air makes it hot – feel the end of a bicycle pump after a speedy session – and hot air is less dense than cold air. Lower density means fewer oxygen molecules per cylinder fill, so you can’t burn as much fuel as you might.

Enter the intercooler. This is a simple radiator set between the turbo and the cylinders, with compressed air from the turbo rushing through the inside and ambient air or (less commonly) water on the outside. The cooler, denser charge it produces is kinder to the engine (less thermal load) and supports the burning of more fuel.

What’s good about it? More power, better efficiency.

What’s bad about it? More weight, plumbing and cost. Potential for delay before boost arrives – ie turbo lag – in poorly-designed setups.

(6) Four valves per cylinder


Valves control the flow of air into and exhaust gas out of the engine cylinder head, and more flow means more potential for power. Normally one inlet and one exhaust valve do the job.

Flow can be increased by making the valves bigger, but eventually this brings problems with valve weight, heat transfer and cylinder head structure and geometry. A better way is to increase valve number, as two smallish valves can control a bigger hole overall than one big one.

What’s good about it? Better efficiency, more power.

What’s bad about it? More complexity.

(7) Closed centre hydraulics


Simple tractor hydraulics use an open centre system. A fixed-displacement pump runs constantly, supplying oil to one or more spool valves. Each spool has a smaller-diameter centre section which lets oil flow freely back to the reservoir (or on to the next valve) when the spool is not operating a service. Oil is pumped constantly round the circuit, whether the valve is operating or not, which heats it up. And as the pump must be big enough to supply all valves in a multi-spool setup, power is wasted when using a single service. Open centre hydraulics suit low-cost, simple tractors.

Modern closed centre hydraulics use a variable-displacement pump. Spools have a solid centre, which blocks oil flow when the valve is in neutral. The resulting pressure rise can trigger pump-shut-off, saving engine power and minimising oil heating.

Using a large pump gives high oil flow at low engine speed, thus good performance. Closed centre hydraulics vary flow and keep pressure constant are more fuel-efficient, need no relief valves, can serve different functions like the linkage, steering and brakes without complicated flow dividers, and more readily let multiple services be used at the same time.

What’s good about it? Faster work using multiple services, as with a foreloader. More fuel-efficient.

What’s bad about it? More complex pump.

(8) CVT gearbox


Also called a stepless gearbox, the CVT is a Constantly Variable Transmission. There are no fixed steps or gears instead an infinite number of ratios between upper and lower limits, variable on the go.

Simple types use a belt and two pulleys – one gets bigger in effective diameter as the other gets smaller, changing the ratio between them. Examples are combine drive sheaves and some ATV transmissions. A basic hydrostatic drive can become a CVT by varying the output of the motor and/or pump.

Simple CVTs vary output speed while letting the engine run at or near its most efficient operating revs, but deliver only a limited span of forward speeds. Today’s tractor CVTs use very efficient hydrostatics, or hydrostatics plus epicyclic gear sets, to generate forward speeds from a few m/hr to 50k. Transmission and engine electronics can interact to expand operating options, and allow wide latitude in engine revs.

What’s good about it? Terrific flexibility in fieldwork plus the possibility to save fuel in transport. Lower operator stress.

What’s bad about it? Cost premium. Less efficient than a mechanical gearbox, though not by much.



In electronics, a BUS is a pathway for information exchange between devices connected to it. ISO, meanwhile, is the fun-sounding International Organisation for Standardisation. Agriculture’s ISOBUS is the specification agreed between manufacturers on how to implement ISO 11783, which in turn is the standard dealing with data communication between a tractor, its implements and computers.

An ISOBUS connection lets, for example, an implement tap in to accurate forward speed info coming from the tractor’s radar, so no extra equipment is needed. Among much else, ISOBUS standardises the protocols and hardware (connectors/cables) required to let any compatible machine talk to any compatible tractor without added controllers.

What’s good about it? One cab control centre – the Virtual Terminal or ISO Terminal – replaces individual machine control boxes and can handle any ISOBUS implement. GPS info is easily accommodated for precision farming applications, and data can be readily gathered, stored and transferred to an office PC. A single breakaway connector eases hook-up.

What’s bad about it? You may end up paying for ISOBUS-ready equipment even though the capability won’t be used. Troubleshooting is dealer territory.

(10) Headland management system

HTS manager

A blanket name for systems which allow a tractor driver to automate (or part-automate) a sequence of events at a headland. For example when ploughing: Shift down two ratios, reduce revs to a pre-set figure, lift the plough, close it, turn it, open it, lower it, increase revs to a pre-set figure, shift up two gears.

Sequences are usually recorded while in work and may be modifiable later. Pauses can be included, either timed or as a permanent interruption until the sequence is restarted by the driver.

What’s good about it? Effective headland management reduces load on the operator and can increase productivity.

What’s bad about it? Some systems are a pain to set up, to use, or both others are too limited to be of real use.

* Any other baffling bits of tractor techno-speak you’d like turned into plain English? Email us on and we’ll do our best.