Chaser Bin Tyres and Tracks Explained: Ratings, Sizes & Soil Impact
Tyre ratings on chaser bins aren't a single number: load index, speed symbol and cyclic loading all interact. Understand how to read the codes, why width, tread and total axle load each affect your soil differently, whether tracks or tyres suit your conditions, and what to check before fitting third-party tracks.
Chaser Bin Tyres and Tracks Explained: Ratings, Sizes & Soil Impact
Inside this article:
- What do chaser bin tyre ratings mean?
- Common chaser bin tyre sizes
- What is cyclic loading?
- How speed changes carrying capacity
- Tyre pressure and load capacity
- How width and tread affect your soil
- Can you put tracks on a chaser bin?
- Matching tyre ratings to your total loaded weight
- Tyre checks that protect your rating
- Quick answers
What do chaser bin tyre ratings mean?
A chaser bin tyre rating tells you how much weight each tyre can safely carry at a given speed and inflation pressure. The markings on the sidewall follow a standard format, and once you can read them, you can check whether your bin, your crop load and your travel speed sit within what the tyres are actually rated to do.
Take the standard fitment on Davimac 30T single and 45T dual-axle models: the Harvest 900/60-32 20pr HB45 185A8 TL. Broken down:
| Marking | Meaning |
|---|---|
| 900 | Section width in millimetres |
| 60 | Aspect ratio: sidewall height is 60% of the section width |
| 32 | Rim diameter in inches |
| 20pr | Ply rating, an indicator of casing strength |
| 185 | Load index, a standardised code for maximum carrying capacity |
| A8 | Speed symbol: rated to 40 km/h |
| TL | Tubeless |
The load index and speed symbol always work as a pair. A tyre rated 185A8 can carry its indexed load at 40 km/h, and these codes are standardised across manufacturers by bodies such as the Tyre and Rim Association of Australia, whose annually updated Standards Manual is the technical reference for tyre and rim data in Australia. The exact kilogram figures for your tyre at each speed and pressure come from the manufacturer's load and inflation tables, such as the Harvest Tyres load and speed rating tables.
The critical point for chaser bin operators is that the sidewall rating is not a single number. Carrying capacity changes substantially with speed, and chaser bins are assessed under a specific tyre service category called cyclic loading.
Common chaser bin tyre sizes
Chaser bins in Australia overwhelmingly run on 32-inch rims, and the same handful of tyre sizes appear across most brands regardless of who built the bin. The sizes fitted to Davimac chaser bins are these industry-standard sizes, so the guidance in this article applies just as well if you are checking ratings on another machine.
| Size | Construction | Where you'll see it |
|---|---|---|
| 30.5L32 | Bias (cross-ply) | The traditional chaser bin tyre in the older imperial format. Its close metric equivalent is 800/65-32. |
| 800/65-32 or 800/65R32 | Bias or radial | The metric successor to the 30.5L32 footprint, available in both constructions. Radial versions are often offered as flotation tyres. |
| 900/60-32 or 900/60R32 | Bias or radial | The most common size on 30 to 45 tonne bins. Roughly equivalent to the older 35.5L32, with a wider footprint and higher load capacity than the 800 sizes. |
| 1050/50R32 and 1250/50R32 | Radial | Very wide singles seen on large-capacity grain carts, more common in North America than on Australian chaser bins. |
Two things in a size designation matter beyond the dimensions. A dash (900/60-32) indicates bias construction, while an R (900/60R32) indicates radial. Radials have flexible sidewalls that spread the footprint under load, while bias tyres have stiffer casings that ride firmer and resist sidewall damage. Both are legitimate choices on a chaser bin, but they behave differently on the soil, which we cover below.
What is cyclic loading?
Cyclic loading is a tyre service classification for machines whose payload rises and falls repeatedly during work, such as chaser bins, combine harvesters and sprayers. Because the tyre only carries its maximum load for short periods between fills and unloads, it can be rated to carry considerably more weight in cyclic service than it could carry continuously on the road.
The Tyre and Rim Association of Australia defines cyclic loading service for grain cart applications with specific conditions. In plain terms:
- The payload gradually changes from transport load up to the maximum allowable load.
- Unloading must occur before any road transport.
- The minimum load must not exceed 60% of the maximum tyre load, so the load genuinely fluctuates rather than sitting near maximum.
- The maximum load may not be carried more than 1.5 km before unloading begins.
This is why Davimac's maximum towing speeds distinguish between distance travelled when loaded. A loaded bin may travel at up to 20 km/h over distances under 1.5 km, but must not exceed 10 km/h over longer distances, and an empty bin is limited to 30 km/h.
Those limits exist to keep the bin inside the tyre manufacturer's cyclic rating conditions, not just as general caution.
Cyclic ratings are an industry-wide concept rather than something unique to one brand. Tyre manufacturers such as Michelin explain in their agricultural load rating guidance that tyres for harvesters and similar machines are rated with these cyclical load patterns built in.
How speed changes carrying capacity
Slower speeds generate less heat and casing stress, so the same tyre at the same pressure can carry significantly more weight at 10 km/h than at 40 km/h. On the tyres fitted to Davimac chaser bins, the difference between road speed and unloading speed is close to double the carrying capacity.
Harvest grain cart tyre ratings by speed
Harvest Tyres publishes the following maximum loads per tyre for chaser bin (grain cart) application, at each tyre's maximum inflation pressure. These loads are covered by Harvest's 7-year guarantee for grain cart application.
| Max load per tyre | 30.5L32 18pr HB45 167A8 | 800/65-32 20pr HB45 179A8 | 900/60-32 20pr HB45 185A8 | 800/65R32 Trojan 185A8/181D |
|---|---|---|---|---|
| Up to 40 km/h | 7,200 kg | 9,300 kg | 11,100 kg | 10,082 kg |
| Cyclic, up to 25 km/h | 8,496 kg | 10,974 kg | 13,098 kg | 10,638 kg |
| Cyclic, at 15 km/h | 12,249 kg | 15,810 kg | 18,870 kg | 14,338 kg |
| Cyclic, at 10 km/h | 13,465 kg | 17,390 kg | 20,757 kg | 15,725 kg |
| Max inflation pressure | 45 psi (310 kPa) | 60 psi (414 kPa) | 60 psi (414 kPa) | 64 psi (441 kPa) |
Source: Harvest Tyres grain cart application ratings, as supplied in the Davimac chaser bin operators manual. Cyclic loads at 15 km/h and up to 25 km/h apply for a distance of up to 1.5 km before unloading must begin. Download the Harvest Grain Cart Tyres info sheet for the full conditions.
Worked example: checking a loaded bin against its tyre rating
A Davimac 35T dual-axle bin fully loaded with wheat has a total loaded weight of approximately 49.3 tonnes (14.3 tonnes empty machine plus 35 tonnes of wheat). Not all of that rides on the bin tyres: 2,200 kg sits on the tractor drawbar as tongue weight, leaving around 47.1 tonnes across the four Harvest 900/60-32 tyres, or roughly 11,800 kg per tyre. Against the table above, the bin sits comfortably inside the 20,757 kg per-tyre rating at 10 km/h, and still inside the 13,098 kg rating at 25 km/h for short runs to the truck.
Run the same numbers on a fully loaded 45T at 62.8 tonnes total, less its 2,950 kg tongue weight, and each of its four tyres carries around 15,000 kg. That is well within the 10 km/h and 15 km/h cyclic ratings, but above the 25 km/h rating. This is exactly why the loaded speed limits matter: the tyres are generously rated for how a chaser bin is meant to be operated, and the margin disappears if a loaded bin is towed at road speeds.
Even distribution across the tyres is an assumption, too. Uneven filling and slopes shift weight between tyres, which is one reason the manual instructs operators to fill the bin evenly and on flat ground. Loaded tongue weights for every model are published on our specifications page.
Tyre pressure and load capacity
Every load figure in the table above assumes the tyre is inflated to its maximum rated pressure, and an underinflated tyre cannot carry its rated load regardless of what the sidewall says. Harvest Tyres covers this principle and the parameters behind working pressures in its tyre pressure guidance.
Air carries the load, not the rubber.
Running below maximum pressure is legitimate and often desirable in the paddock, since lower pressures spread the footprint and reduce ground pressure. The trade-off is reduced carrying capacity, so the correct pressure for your operation depends on your actual per-tyre load, travel speed and distances. The tyre OEM's load and inflation tables are the authority here, and it is worth a call to the manufacturer if your setup does not match a published scenario.
Pressure should be checked weekly during the season, and both over-inflation and under-inflation carry real costs: under-inflation causes bead slippage and sidewall damage, while over-inflation increases soil compaction and machine bounce. Our guide on how to check your chaser bin tyre pressure covers the checking procedure and the safety steps for inflating large agricultural tyres.
Maximum inflation pressures
Maximum inflation pressures for the standard Davimac tyre options are set out below.
| Tyre size | psi (max) | kPa (max) |
|---|---|---|
| Harvest 30.5L32 18pr HB45 167A8 TL | 45 | 310 |
| Harvest 800/65-32 20pr HB45 179A8 TL | 60 | 414 |
| Harvest 900/60-32 20pr HB45 185A8 TL | 60 | 414 |
| Harvest 800/65 R32 Trojan R3 Flotation | 64 | 441 |
How width and tread affect your soil
A fully loaded chaser bin is one of the heaviest machines that will cross your paddock during harvest, so the tyres are not just a load-carrying decision. They determine how much of that weight the soil feels, and where.
Tyre width
Width is the biggest factor. Ground pressure is load divided by contact area, so at the same load and inflation pressure, a wider tyre spreads the weight over a larger footprint and pushes less force into the soil profile. Moving from an 800-section to a 900-section tyre adds roughly 100 mm of width per tyre, and the difference compounds across four tyres on a dual-axle bin. This is why grain cart tyre suppliers publish footprint comparisons: NTS Tire Supply's grain cart tyre comparison shows how total footprint area changes with tyre size and construction, and how that maps to estimated compaction.
Tyre Tread
Tread pattern and construction matter too. Traction (R-1) lug treads bite into the soil for grip, which also means more surface disturbance. Flotation (R-3) treads are shallower and more closely spaced, designed to ride over the soil rather than dig into it, trading traction for reduced disturbance. On a towed machine like a chaser bin, which does not need to generate its own drive traction, a flotation tread gives up little in practice. This is the reasoning behind the Harvest Trojan R3 flotation option on Davimac bins. Radial construction adds to the effect, since the flexible sidewall lengthens the contact patch under load compared with a stiffer bias casing at the same pressure.
Surface compaction vs subsoil compaction
Footprint only tells half the compaction story, and it is worth being precise about which half. GRDC research into subsoil compaction confirms that compaction near the surface is governed by contact pressure, load divided by footprint, which is exactly what wider tyres, flotation tread and lower inflation pressure address. But compaction depth in the subsoil is driven by total axle load, not footprint, so a heavier machine can still drive compaction deeper even while a wide tyre or track keeps the surface looking undisturbed.
That has a direct, practical consequence: spreading a heavy load over a wider footprint reduces surface damage, but it does not automatically fix the deeper problem if the total weight on that axle is high. Subsoil compaction is also the more expensive kind to correct, since it sits below normal tillage depth and can persist for multiple seasons. The two levers that actually address total axle load are keeping loaded travel to the minimum necessary and confining wheel tracks, whatever they run on, to the same ground every year.
Controlled Traffic Farming
None of this replaces good traffic management. Compaction from harvest machinery persists well below the surface, which is why CTF-adjustable wheel centres are standard on Davimac 25-35T models, letting the bin run on the same wheel tracks as the rest of your gear.
Can you put tracks on a chaser bin?
Yes. Davimac chaser bins are compatible with certain universal third-party track systems, and several Davimac bins in the field already run them, however they currently must be sourced, fitted, and warranted directly through the track supplier. Other manufacturers also offer track undercarriage options.
What tracks change
A track system spreads the bin's weight over a much larger contact area than any tyre can, so peak ground pressure drops further than even a wide flotation radial achieves. In a wet harvest or on soft country, that can be the difference between carting grain and leaving it in the paddock. As with wide tyres, though, a lower surface footprint does not by itself reduce subsoil compaction if the bin's total loaded weight stays the same; see surface vs subsoil compaction above.
The track trade-off
Tracks cost considerably more than a tyre set, add weight to the machine, and introduce more wearing parts (belts, idlers, rollers and bearings) that need inspection, tightening, and maintenance through the season. On firm ground they can scrub in tight turns, and transport speeds and time-on operation are typically lower than on tyres. Tracks run hotter than tyres at road speed, which is a further reason track-equipped bins are generally better suited to staying within the paddock and short local moves rather than long road transfers between blocks. For most farms, a wide flotation tyre at the correct pressure delivers most of the compaction benefit covered in the width and tread section above at a fraction of the cost and complexity, which is why tyres remain the standard fitment on chaser bins.
Fitting third-party tracks to a Davimac
If tracks stack up for your conditions, work through these points with the track supplier before committing:
- Load rating. Confirm the track system is rated for the bin's total loaded weight, using the same method set out below for tyres: total loaded weight, less tongue weight, divided across the track assemblies.
- Hub and axle fit. Confirm the track system's mounting matches, or that the supplier will manufacture the adaptor parts required. Davimac bins require custom mounting parts for universal tracks.
- Track gauge and CTF. If you run controlled traffic, confirm the fitted track centres match your system, the same check you would make on wheel centres.
- Transport dimensions. Track assemblies can change the bin's overall width and clearances. Rubber tracks often come in 25", 30" and 36" widths. Recheck transport requirements for your state before moving the bin on public roads.
- Warranty. Davimac's factory warranty covers the bin itself, but does not extend to third-party track systems or faults arising from their installation.
Supply, fitment and support all run through the track manufacturer rather than Davimac, and some installations require custom parts to be made. We recommend talking to our sales team before committing.
As a general rule: dry, firm harvests and country with long road transfers between blocks favour tyres; wet, late finishes and soft ground favour tracks, provided the total loaded weight is still managed with CTF and sensible loading practices either way.
Matching tyre ratings to your total loaded weight
The tyre rating is one layer of a chaser bin's overall load capacity, alongside the axle rating and the empty machine weight. Davimac single-axle models carry a 40-tonne axle rating and dual-axle models an 80-tonne rating, but the actual undercarriage capacity is always subject to the fitted tyre specification. In practice, the tyres are usually the governing limit, which is why they deserve more attention than they typically get.
The working method is straightforward. Calculate your total loaded weight (empty machine weight plus crop load), subtract the tongue weight carried on the tractor drawbar, divide the remainder across the number of tyres, and check the result against the OEM's cyclic rating for the speed you intend to travel. Crop load varies significantly with bulk density, so a bin that is at capacity with lentils behaves differently to the same bin with oats.
Our grain weight and density chart walks you through the full calculation with per-crop capacities for every model.
Tyre ratings are also worth checking whenever you change tyres, since all Davimac chaser bins can be fitted with a range of tyre options and any replacement should meet or exceed the load and speed ratings specified by the OEM. On dual-axle bins, all four tyres must be matching sizes: mismatches shift load unevenly between tyres and cause overloading and premature failure.
Tyre checks that protect your rating
A tyre's rated capacity assumes it is in sound condition. Inspect tyres regularly for cuts, cracks, abnormal wear, bulges or embedded objects, and replace any tyre showing damage or deterioration. Check wheel nut torque daily for the first three days after fitting and weekly after that, and keep tyres clear of oils, fuels and solvents that degrade the rubber. Tyre changing carries serious risks and should only be performed by trained personnel with the correct equipment.
Full tyre safety procedures, torque specifications and the OEM tyre information sheet are included in the chaser bin operators manual, available on our manuals page.
Quick answers
Are tracks better than tyres for chaser bins in Australian conditions?
It depends on your soil and season, but generally the answer is no. Tracks spread weight over a much larger footprint and keep moving in wet, soft conditions where tyres would bog, which suits late or wet harvests. On dry, firm country (typical in large parts of the Australian wheat belt) a correctly specified flotation tyre at the right pressure delivers most of the same reduced-compaction benefit for a fraction of the cost, complexity and maintenance, which is why tyres remain the standard fitment.
What is the difference between surface and subsoil compaction?
Surface compaction is caused by contact pressure, load divided by footprint, so wider tyres, flotation tread and correct inflation pressure directly reduce it. Subsoil compaction is caused by total axle load regardless of footprint, so a wide tyre or track can look gentle on the surface while still driving compaction deeper if the bin is heavily loaded. Managing both means addressing footprint and total loaded weight together, not just one or the other.
Can I fit tracks to a Davimac chaser bin?
Yes. Davimac bins are compatible with certain universal third-party track systems, and several are already running in the field. Fitment requires custom mounting parts, and supply, warranty and support for the track system itself run through the track supplier rather than Davimac.
Does towing a chaser bin on tracks affect road transport?
Yes. Track-equipped bins generally travel slower on the road than tyre-equipped bins and run hotter at speed, so they suit paddock work and short local moves better than long transfers between blocks. If most of your cartage happens on public roads over distance, a tyre-based bin is usually the better fit.
What tyre size do most Davimac chaser bins run?
The most universal fitment across 25 to 45 tonne models is the Harvest 900/60-32 20pr HB45 185A8 TL for its large weight rating and wider footprint. 30.5L32 18pr HB45 167A8 tyres are popular on 30-35T dual axle bins as they handle those loads well and reduce cost. Trojan R3 flotation tyres are a great option for softer ground conditions (such as in QLD and parts of NSW and VIC) or farmers conscious of soil impact. All Davimac chaser bins run on 32-inch rims with 12-stud hubs.
