Combine settings: cleaner grain and less loss at harvest

Why combine setup is worth the effort

Harvest is the moment a whole year of work is paid out or lost. A combine that is set well keeps clean, undamaged grain in the tank and leaves very little behind. A combine set badly throws grain out the back, cracks what it keeps, or fills the tank with chaff and weed seeds. The crop looks the same from the cab, but the bottom line is very different.

This matters whether you farm thousands of acres of US wheat or a few hundred acres of UK cereals. On big acreage, even a small percentage of loss adds up to a serious tonnage across the season. On a smaller farm, every tonne counts harder. Before you upgrade or hire a machine, it pays to compare machine specs on FarmFleets so you understand the capacity and features a model really offers.

How a combine separates grain from everything else

It helps to picture the job in stages. First the header gathers and cuts the crop and feeds it in. Then the threshing system rubs the grain free from the straw and chaff. Next the separation system shakes or spins out the last of the grain. Finally the cleaning system uses sieves and a fan of air to drop clean grain into the tank while blowing the lighter rubbish away.

Every stage has settings that affect the others. Open the concave too far and you leave grain in the straw. Close it too far and you crack grain and overload the cleaning system. Turn the fan up and you blow chaff away, but too much and you blow grain out too. Good setup is about balance across the whole machine, not chasing one dial.

The main settings and what they do

Drum or rotor speed and concave gap control threshing. Faster and tighter knocks more grain free but risks cracking it and creating more rubbish to clean. Slower and more open is gentler but can leave grain behind. You want the gentlest setting that still threshes the crop fully, which protects sample quality and seed if you are saving it.

The fan and sieves control cleaning. The fan blows air up through the sieves to lift away chaff. The sieve openings decide what falls through to the tank and what carries on. Too much air or sieves set too tight push grain over the back. Too little air or sieves too open let dirt and weed seeds into the tank. Modern machines show many of these on screen, part of the wider shift to AI decision tools on the farm.

• Drum or rotor speed: threshing aggression.
• Concave gap: how hard the crop is rubbed.
• Fan speed: how much chaff is blown away.
• Sieve openings: what reaches the grain tank.
• Forward speed: how much crop the machine has to handle.

Finding and reading your losses

The grain tank only tells you what you kept, not what you lost. To set a combine well you must check behind it. Stop in a representative part of the field, look on the ground behind the machine and count the grain you find in a known area. Many operators use a simple tray or pan to catch what comes out the back of the sieves and the straw walkers or rotor.

This tells you where the loss is happening. Grain still in unthreshed heads points to the threshing setup. Loose grain blowing out the back points to cleaning or speed. Free grain over the straw walkers points to separation or driving too fast. Fixing the right thing matters, because cranking the wrong setting often makes a different problem worse. Patience here is rewarded across the whole harvest, which ties into our guide to harvest logistics.

Driving speed and feeding the machine evenly

Forward speed is one of the most powerful settings of all, and it is free. Drive too fast and you cram more crop through than the machine can thresh and clean, so losses climb and the sample suffers. Slow down and the same machine handles the crop properly. The fastest harvest is not always the quickest ground speed, it is the speed that keeps losses low and the tank clean.

Even feeding matters too. A combine works best with a steady, full feed across the width of the header. Ragged, lumpy feeding upsets the threshing and cleaning and causes surges of loss. Adjust the header height, reel speed and your driving to keep the flow even. In laid or weedy crops you will often need to slow down and lift losses checks, rather than push on and hope.

A useful habit is to find the speed where losses start to climb, then back off a touch and settle there. Pushing right to the edge of the machine's capacity feels productive but often costs more grain than the extra ground is worth. Conditions change through the day, so the right speed in the cool morning crop will not be the right speed by mid-afternoon. Treat ground speed as a live setting you adjust, exactly like the fan, sieves and concave.

Adjusting through the day and the season

Crops change, and so should your settings. A crop is tougher and damper in the cool of the morning and after dew, then dries out through the afternoon. Dry crop threshes more easily and shatters more readily, so you may open the concave or back off the drum as the day warms. A quick loss check at a few points in the day keeps you honest.

Different crops need very different baselines too, from cereals to oilseeds to beans. Start from the manufacturer's recommended settings for that crop, then fine-tune from your own loss checks. Keeping a note of what worked builds a useful record over the years, which sits alongside the wider question of farm data ownership as more of this information lives in the machine's software.

What operators should check

Run through this list when you start a field and again if conditions change or the sample looks wrong. A few minutes of checking saves far more than it costs.

• Loss check behind the machine in a known area.
• Grain sample in the tank for cracks and rubbish.
• Threshing first: drum speed and concave gap.
• Cleaning next: fan speed and sieve openings.
• Forward speed matched to crop and machine capacity.
• Header height and reel set for an even, full feed.

Looking after the grain after the combine

Good combine setup is only half the job. The grain you keep still has to be moved and stored without spoiling. Grain that comes in damp or damaged is more likely to heat and lose value, so quick, careful handling and the right drying and storage matter just as much as the field work. A clean sample from a well-set combine is far easier to store safely.

Plan the whole chain, from header to store, before harvest starts. That means trailers and handling ready, and drying and storage in good order. Our guide to grain storage and energy efficiency covers keeping that grain in top condition once it leaves the field. The aim across the whole system is simple: keep as much value as possible, from the standing crop right through to the buyer.

It is worth remembering that a combine sets the pace for the whole team at harvest. If it is poorly set and has to crawl or keep stopping to clear blockages, trailers and dryers sit idle and the weather window slips away. A few minutes spent setting the machine well at the start of each field protects not just the grain in front of you, but the rhythm of the entire operation and everyone working with you that day.

Sources and method

This guide was written in plain English from current public farming and machinery information checked in 2026. It draws on widely available manufacturer sheets, dealer records and general harvesting good practice, with no single source named.

FarmFleets encourages you to compare specs, photos, recalls and source confidence before buying or hiring a combine. Always start from your machine's own crop settings and confirm with real loss checks in your fields, because no guide can replace what the ground behind the combine tells you.