What size chaser bin do I need?
Correctly sizing a chaser bin means matching header class, truck loads, crop density and carting distance. A '30T' from one brand doesn't hold the same grain as another. This guide works through the maths so you buy the size your harvest system actually uses, not the biggest number on the brochure.
What size chaser bin do I need?
Size the chaser bin to hold at least two full header tanks, three for extra margin, so the header never stops to wait for it.
That's the baseline. The exact number depends on five factors working together:
- Header capacity
- Mother bin or truck?
- Crop type
- Carting distance
- Tractor capability
Work through these five factors in order and the right size becomes clear by the end.
Step 1: Start with your header's capacity
The chaser bin's job is to stop the header waiting. Start with how much grain the combine harvester produces per tank, since that sets the floor for bin size.
Header capacity keeps climbing. The newest class 10+ combines carry grain tanks up to 20,000 litres which is around 16 tonnes of wheat.
Approximate wheat weights by header class:
|
Header/Combine class |
Grain tank (approx.) |
Wheat per tank (approx.) |
|---|---|---|
|
Class 7 |
9,000 to 10,500 L |
7 to 8.5 t |
|
Class 8 |
10,500 to 12,500 L |
8.5 to 10 t |
|
Class 9 |
12,500 to 14,500 L |
10 to 11.5 t |
|
Class 10 |
14,500 L and up |
11.5 to 13 t |
Working rule: size the bin to hold at least two full header tanks, three for more margin. Two fills keeps the header moving under normal conditions. Three covers truck delays, longer carting distances, and hold-ups at the ramp without the header stopping.
Note this number and move to the next factor; it isn't the final size yet.
Step 2: Check what's waiting at the fence line
What the bin feeds next depends on your setup. A growing number of operations run a mother bin as the buffer between chaser and truck: the chaser tips into the mother bin at the paddock edge, and the mother bin loads the truck separately, on its own schedule.
In that case the chaser's cycle only needs to keep the mother bin fed, which takes pressure off getting the chaser size exactly right.
Where the chaser tips straight into the truck, truck capacity is the second constraint, and it isn't one fixed number. Legal payload depends on the truck's axle configuration and which mass management scheme it's registered under, and both vary by state.
As a rough illustration from NSW's Grain Harvest Management Scheme: a common 6-axle prime mover and semi-trailer runs from around 42.5 tonnes up toward 45 tonnes or more depending on registration concessions; a 7-axle B-double spans roughly 50 to 57 tonnes-plus; road train combinations go further again. Treat these as a sense of scale, not a number to size a bin against, since they shift by state, scheme and permit.
Whichever state you're in, ask your carrier what their trucks actually load to in practice; usable payload sits below the legal maximum once tare weight and a safety margin are accounted for.
Step 3: Adjust for crop density
Davimac bin capacities are quoted in wheat tonnes at 0.8 kg per litre. Lighter commodities take the same volume at less weight, so a bin never carries its wheat rating in canola, oats or some barleys.
Example: a 45T Davimac bin holds 59.5 cubic metres level, which is roughly 40 tonnes of canola rather than 45 of wheat.
Compare bins by volume (litres or cubic metres), not the tonnage on the decal, especially across brands. Two '30T' bins from different manufacturers can hold genuinely different amounts of grain; Kondinin Group's chaser bin research recommends the same volumetric approach.
Check your own rotation against our chart to see the actual carrying capacity of a chaser bin before committing to a size.
Step 4: Factor in carting distance
Distance to the truck or mother bin changes the calculation. Short distances favour a smaller bin cycling quickly, since the round trip costs little time. Longer distances (4 km or more across the paddock) favour a bigger bin making fewer trips, even where header-fill maths alone wouldn't demand it.
Kondinin Group's harvest research puts post-maturity yield losses at around half a per cent a day when harvest is delayed. A bigger bin buying slack in the system, against truck delays, driver changeovers, a breakdown at the ramp, is effectively insurance against that cost.
Step 5: Check it against your tractor
Confirm the size you've landed on can actually be towed. Check the tow weight capacity in your tractor's manual, the drawbar tongue weight (Davimac loaded tongue weights run roughly 2,200 to 4,800 kg depending on model), horsepower, and hydraulic remotes (three minimum, four for the 45T, more again for hydraulic options). A loaded 45T grosses over 60 tonnes; even a loaded 25T is north of 33.
If the tractor has no PTO, check whether hydraulic auger drive is available, which trades a slower unload for compatibility.
Putting it together
Combine the five factors: start with at least two header tank fills, check that against what's waiting at the fence line, whether that's a truck directly or a mother bin, adjust up for lighter crops, adjust up again for longer carting distances, and confirm the result against your tractor.
We recommend choosing a bin that is slightly larger for your needs to ensure capacity and future-proofing your investment. However, speccing significantly above the size your system actually uses adds unnecessary tare weight, and tread and towing demand without a corresponding benefit.
Typical outcomes:
- A single header up to class 8 on a moderate carting distance sits on a 25T to 30T bin.
- A class 9 header, or a longer carting distance, moves that to 30T or 35T.
- Two headers, a class 10 machine, or a mother bin feeding B-double carting is where the 45T applies.
For context, Kondinin Group's 2024 National Agricultural Survey found 44 per cent of surveyed farmers owned a chaser bin over 30 tonnes, averaging 31.8 tonnes. Most operations, working through the same factors, land in a similar range.
Size to match your header, your truck or mother bin, and your paddock.
Other factors beyond size:
Axle type and configuration, auger system, build quality, running gear and available options are all important factors to consider when choosing a chaser bin. Compare every model in the Davimac chaser bin range to find the best machine for your operation.
Quick answers
How many header tanks should a chaser bin hold?
At least two full header grain tanks, three for more margin. Two fills keeps the header moving in normal conditions; three covers truck delays and longer carting distances without the header waiting on the bin.
What size chaser bin suits a class 9 header?
A class 9 header carries roughly 10 to 11.5 tonnes of wheat per tank, so a 30 to 35 tonne chaser bin holds around three fills and keeps the header harvesting. Two class 9 headers push the answer to 35 to 45 tonnes.
Does crop type change what size bin I need?
Yes. Capacities are quoted in wheat tonnes at 0.8 kg per litre. Lighter crops like canola and oats fill the bin's volume at less weight, so a 45T holds roughly 40 tonnes of canola. Rotations heavy in light commodities should size up.
