Why Axle Loads and Flotation Matter for Slurry and Muck
Slurry and muck tankers are heavy at full load, clock up road miles, and must still work on soft soils. Axle load, tyre size and inflation pressure determine contact patch and ground pressure. Get them wrong and you cause ruts, compaction and failures. Get them right and you stay road legal, protect soils and extend tyre and wheel life.
Most tankers and spreaders run single, tandem or tri-axle bogies; some use steering axles to cut scrub and turning damage. Correctly inflated flotation tyres spread the load and reduce sinkage. Start with accurate calculations, then select the tyre and wheel to suit. For background, see our complete guide to flotation tyres and wheels.
Step 1: Gather the Right Weights and Dimensions
Before specifying tyres or wheels, record the essentials:
- Unladen (tare) weight of the tanker/spreader
- Maximum payload (use realistic slurry/muck density; typically 1.00–1.10 t/m³)
- Gross vehicle weight (GVW) when full
- Axle count, axle spacing, and wheelbase to the drawbar pin
- Current tyre sizes, rim widths and track width
- Drawbar nose-weight range on the tractor
Use a weighbridge empty and full. If possible, capture per-axle weights as well as drawbar load. Expect variation from liquid surge, slopes and braking, and build in a safety margin. If you need a method to convert weight to ground pressure, read our ground pressure calculation guide.
Step 2: Calculate Axle Loads and Distribution
Convert GVW to axle loads using simple statics. Measure axle spacing and estimate the centre of gravity (mid-tank when full is a good start). On a two-axle bogie, the static split depends on CG position relative to the bogie midpoint and on suspension rates. Steering axles or softer springs may carry less on-road but more in-field over bumps.
Part of the weight is carried by the tractor via the drawbar. Subtract drawbar load from GVW to find what the trailer axles must carry. This also informs tractor rear tyre pressures and legality. Add allowance for dynamics (braking, potholes, cambers). For speed and weight rules, see our note on ag roadwork tyre load and speed compliance.
Step 3: Convert Axle Loads to Per‑Tyre Load and Choose LI/SI
Divide each axle load by the number of tyres on that axle/bogie to get per-tyre load. Add 10–15% for side-to-side imbalance, slopes and dynamic effects. Select a tyre whose Load Index (LI) at the required Speed Index (SI) and pressure carries that adjusted load, and ensure the wheel load rating also matches.
Typical trailer speeds are A8 (40 km/h), B (50 km/h) or D (65 km/h). Capacity changes with speed and pressure, so use the tyre maker’s tables. As a quick guide (single fitment):
- LI 164 ≈ 5,000 kg
- LI 166 ≈ 5,300 kg
- LI 170 ≈ 6,000 kg
Some trailer tyres offer IF/VF technology, allowing the same load at lower pressure for better flotation. Heat build-up on long hauls still applies; keep within approved duties and OEM guidance.
This image was generated with AI and may not always represent the product or service exactly.
Step 4: Pick Flotation Sizes and Target Ground Pressure
Set a ground pressure target by soil and season. On wet clays, aim as low as practicable; on firmer summer ground you have more headroom. Shortlist sizes that carry your per-tyre load at low field pressures and still meet your speed rating. Popular tanker/spreader sizes include 560/60R22.5, 650/55R26.5, 710/50R26.5, 750/60R30.5 and 800/45R30.5. Confirm mudguard/chassis clearance, rolling radius and approved rim options before you choose.
Central tyre inflation systems (CTIS) widen your operating window: drop pressures in-field, raise them for the road. Always follow the tyre maker’s load/inflation data. For methods and examples, see our ground pressure guide.
Step 5: Specify the Wheel Correctly: Rim, Offset and Load
Match the tyre to the correct rim width and profile (W, DW, TW) to support the bead and keep the footprint even. IF/VF tyres are sensitive to rim profile, so follow the data. Our note on rim profiles for IF/VF tyres explains why it matters.
Set offset for mudguard and chassis clearance, track width and stability. Measure PCD, hub type (stud vs hub‑piloted), centre bore and nut seat type accurately; see how to measure PCD and hub type. Specify wheel centre, dish and rim load ratings to match your calculated axle loads with margin. Fieldens OTR Ltd designs and builds bespoke wheels to ISO 9001 with the right material thickness, weld spec and coatings for harsh slurry work.
Step 6: Inflation Management, Heat and Puncture Protection
Set cold inflation using approved load/speed tables. After the first long road run, recheck pressures and monitor temperature. Persistent heat indicates under-inflation, overload or excessive speed for the tyre’s rating—adjust to suit the duty cycle.
Gateways, stony tracks and clamp yards raise puncture risk. Fieldens OTR Ltd offers Tyrefill for low-speed, high-risk tasks. It eliminates punctures and downtime but adds weight and retains heat. For higher-speed tankers we will advise where it is suitable, or propose alternatives.
This image was generated with AI and may not always represent the product or service exactly.
Compliance Checklist: Staying UK Road Legal
- Match tyre LI/SI to plated axle and gross weights at actual operating speed.
- Confirm overall width and mudguard coverage meet UK regulations.
- Ensure no tyre-to-chassis contact at full suspension travel and full lock.
- Check tread condition, E‑marking where applicable and correct road pressures.
- Document weights, pressures and settings, and review manufacturer data regularly.
For a refresher on ratings and speeds, see our guidance on UK ag roadwork compliance. Fieldens OTR Ltd can verify your specification before build and fitting.
Worked Example: 3,000‑Gallon Slurry Tanker
Inputs: tare 6.0 t; capacity 3,000 gal (13.64 m³); slurry density 1.03 t/m³ → payload ≈ 14.1 t. GVW ≈ 20.1 t. Assume 2.5 t on the drawbar (tractor), leaving 17.6 t on the tandem bogie. With a near‑central CG, take a 51/49 static split: Axle 1 ≈ 9.0 t; Axle 2 ≈ 8.6 t.
Per‑tyre loads (two tyres per axle): 4.5 t and 4.3 t. Add 15% safety → design for ≈ 5.2 t per tyre. Shortlist 710/50R26.5 and 750/60R30.5, both available in LI ≥ 166 and SI A8/B/D depending on brand. Indicative pressures: field 1.0–1.4 bar; road 3.0–4.0 bar (always use maker tables). Expect a wider, longer footprint and less rutting versus narrow fitments, especially on moist soils.
How Fieldens OTR Designs, Builds and Fits the Right Package
Fieldens OTR Ltd measures your machine on site, models the wheel in CAD and manufactures to ISO 9001. We specify dish, rim profile, material thickness and welds to match real axle loads and duty. Assemblies are built and torqued precisely for reliable service.
We supply leading tyre brands and patterns for slurry and muck work, including Michelin, BKT and ATG. We optimise size, LI/SI and inflation for your routes and soils. We also offer UK‑wide fitting and aftercare to keep you moving. Ready to discuss your tanker or spreader? Contact Fieldens OTR Ltd for a bespoke tyre and wheel package.
FAQs
Are VF trailer tyres worth it on tankers?
Yes—when you need lower field pressures without upsizing the tyre. They improve flotation and reduce compaction. Check heat build‑up and speed limits against your haul distances.
Can I mix tyre sizes or brands on a bogie?
No. Different rolling radii and stiffness upset load share and steering, increasing wear and risk. Always fit matched sizes and casings across the bogie.
What ground pressure should I aim for?
As low as practical for the soil and season. On wet clays, target the lowest pressure that still carries the load at working speed. Use maker tables and calculate contact area first.
How do I choose the right rim for a flotation tyre?
Match the tyre’s approved rim width and profile to support the bead and footprint. If in doubt, see our guide to rim profiles and bead seats and ask our team.
Is CTIS worth fitting to a spreader?
Often, yes. It lets you run low pressures in the field then raise them for the road, protecting soils and tyres. Payback depends on haul distance, average speed and field time.
Can Tyrefill be used in flotation tyres?
For slow, high‑risk jobs it can remove punctures and downtime. On faster tankers, added heat and weight may be limiting. We will advise based on your duty cycle.