Trailer logistics: keeping the combine moving

The combine is the most expensive machine on the farm and the only one that makes money by moving, so trailer logistics has one rule: the combine never waits. How many trailers that takes isn't a matter of feel — it's two numbers. How fast does the combine make grain, and how long does a trailer's round trip to the store take? Everything else is detail.

Here's the arithmetic, where it breaks in practice, and the fixes that actually work.

First number: what the combine produces

Spot workrate in hectares per hour is roughly header width in metres, times forward speed in km/h, divided by ten — then knocked back by a field efficiency of 60-80% for turns, unloading, and the odd blockage.

Worked example: a 9-metre header at 6 km/h is 5.4 ha/hr flat out; at 70% efficiency, about 3.8 ha/hr in the real world. In 9 t/ha wheat that's roughly 34 tonnes an hour — which fills a 14-tonne trailer about every 25 minutes, all day. (Swap in your own kit and crop with the combine workrate calculator.)

That 25-minute drumbeat is the number the whole chain dances to. It shortens in big crops and widens in thin ones, which is why a trailer fleet that coped in the 7 t/ha barley suddenly can't keep up in the 10 t/ha wheat.

Second number: the round trip

Time a full cycle honestly: load alongside the combine, road to the store, weigh, queue, tip, weigh out, road back, and getting back into position. Not the optimistic version — the version with a tractor behind a caravan on the B-road and one trailer already on the pad.

Then the sums: trailers needed is round-trip time divided by the fill interval, rounded up, plus a margin. If the round trip is 50 minutes and the combine fills a trailer every 25, two trailers only works if absolutely nothing slips — so it's really three. At 75 minutes round trip, three is the bare minimum and four is comfortable.

Round trip	Fill interval 25 min	Fill interval 35 min
25 min	2 trailers	1-2 trailers
50 min	3 trailers	2-3 trailers
75 min	4 trailers	3 trailers

The margin matters because the arithmetic assumes a steady state, and harvest never is. One breakdown, one slow tip, one road delay, and a no-margin plan has the combine sat with a full tank.

Where the chain actually breaks

Three places, usually:

The queue at the pad. The round trip that took 40 minutes at 9am takes 55 by mid-afternoon because trailers are stacking up to weigh and tip. Queues compound: each delayed trailer delays the next, and by 4pm the combine is waiting. If the pad is the bottleneck, adding trailers makes the queue longer, not the combine happier.

The drier. If wet grain has to go through the drier before the wet bin is empty, the drier's throughput — not the trailer count — caps the whole day. A 100 t/day drier behind a 34 t/hr combine is full by mid-morning; the choice becomes cut drier fields or stop.

Road distance. Outlying land at 20 minutes each way turns every round trip into an hour-plus, and the trailer requirement jumps. This is where hired help gets weighed up — a tractor, trailer and driver hired in typically runs somewhere around £45-£60 an hour at recent contractor rates (varies by region and kit), which over a fortnight of long-haul carting is a real number: 12-hour days for 10 days lands £5,000-£7,000. Sometimes that's still cheaper than a stopped combine. Do the sum, don't guess it.

The fixes, in rough order of sense

• Bigger trailers before more trailers — one driver moving 18 tonnes beats two moving 14 each, if the tractors and the gateways can take it. Mind the limits: GB tractor-trailer combinations are capped at 31 tonnes gross with the trailer at 18.29 tonnes laden — check current gov.uk/DVSA guidance and see trailer weight limits before speccing up.
• A chaser bin decouples the combine from the road entirely: the combine unloads on the move, trailers load at the headland. Expensive, but on big blocks or soft ground it's the difference between 60% and 80% field efficiency.
• Staging heaps for outlying land: cart to a temporary heap on a pad or stubble nearby, keep the combine fed with a short cycle, and shift the heap with an artic (about 29 tonnes a hit) in slower time. Watch the weather and don't leave wet grain sitting.
• Fix the pad, not the fleet, if the queue is the problem: a second tip point, tipping and weighing split apart, or someone dedicated to running the pad at peak.

Every trailer still gets recorded

Speed is no excuse for blind loads. Whatever the setup — chaser bin, staging heaps, hired artics — every load still needs its ticket: weight, crop, field, destination. Staging heaps are precisely where field identity goes to die, because the heap mixes three fields and the artic driver wasn't there when any of them were cut. Record at the first tip, and the whole team stays on the same numbers no matter how convoluted the route to the shed.

Frequently Asked Questions

How many grain trailers do you need at harvest?

Divide the trailer round-trip time by how often the combine fills one, and round up with a margin. A combine cutting 34 t/hr fills a 14-tonne trailer every 25 minutes; with a 50-minute round trip that's three trailers in practice. Time your own round trip honestly — the queue at the store counts.

How much grain does a combine cut per hour?

Header width (m) times speed (km/h) divided by ten gives hectares per hour flat out; multiply by 60-80% for real field efficiency, then by yield. A 9m header at 6 km/h at 70% efficiency covers about 3.8 ha/hr — roughly 34 t/hr in a 9 t/ha wheat.

Is a chaser bin worth it in the UK?

On large blocks, long fields or travelling-shy ground, often yes — unloading on the move lifts field efficiency markedly and keeps trailers off the soil. On small fields close to the store, the money is usually better spent on trailer capacity or sorting the bottleneck at the pad.

What's the weight limit for a tractor and grain trailer on the road?

In GB the combination is limited to 31 tonnes gross, with the trailer itself at a maximum of 18.29 tonnes laden — which is why an 18-tonne trailer can't legally carry 18 tonnes of grain plus its own weight. Rules change, so check current gov.uk/DVSA guidance before harvest.