Why Flotation Wheels And Ground Pressure Matter
Imagine unloading an 18 t tandem spreader into a wet spring field and watching deep ruts form behind every pass. That’s the moment many realise wheel choice costs more than rubber — it costs yield. This guide is for UK farmers, contractors and fleet managers who specify trailer and implement wheels and want a practical, engineering-led way to size tyres and set pressures.
In our experience, getting footprint and inflation right is the single most effective step to reduce compaction, rutting and fuel use. Read on for a step‑by‑step method, a quick checklist, what usually goes wrong and the minimal data Fieldens OTR Ltd needs to spec a correct package.
Key Terms And Units You’ll Use
Pressure: kilopascals (kPa) or pounds per square inch (psi). Load: kilograms (kg) or kilonewtons (kN) — 1 kN ≈ 102 kg. Contact area: square metres (m²). Tyre section width: millimetres (mm). Footprint length: millimetres or metres.
A common issue we see is confusing static and dynamic loads. Static is parked weight; dynamic loads rise with braking, cornering and bumps. Field speeds allow lower pressures; road work needs higher pressures for heat control. For background on tyre families and construction see the ultimate guide to tractor tyres.
Before You Start: Gather Accurate Inputs
Start with facts, not guesses. Use a weighbridge to confirm gross vehicle mass and axle splits both laden and unladen. Record tyre count per axle (single/dual), track width, typical and maximum speeds, and the share of field versus road work.
Also note soil condition (dry, moist, wet), slope, headland turning and any likely load shift (for example slurry). These change your safety margin and pressure choice. If you’re working with towed equipment, our guide on choosing the right trailer axle and wheels is helpful.
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Step 1 — Set Target Ground Pressure
Pick a practical target average ground pressure below your soil’s bearing strength. In UK field work 60–120 kPa is common; aim lower on wet soils or repeated passes. Remember lower targets usually mean larger tyres or more tyres per axle and higher capital cost.
This target becomes the ceiling for working inflation pressure in the field. If your current tyres can’t meet it, plan for wider or higher‑volume tyres or additional tyre count.
Step 2 — Calculate Required Contact Area Per Tyre
Find load per tyre: axle load ÷ number of tyres on that axle. Convert mass to kN for the formula (1 t ≈ 9.81 kN). Then:
Required Area (m²) ≈ Load (kN) ÷ Target Pressure (kPa). Add a 10–15% margin for braking, slopes and load shift. That area drives section width and footprint length — undersize and you increase crown pressure and compaction.
Step 3 — Convert Area Into Tyre Size And Wheel Width
Estimate footprint length by dividing area by expected section width. Choose a flotation size family that achieves the footprint at your target pressure and operational speed. Match rim width to the tyre maker’s recommendation — a common error we see is fitting wide tyres to narrow rims, which crowns the tread and raises ground pressure.
Confirm PCD, centre bore, offset and track width to suit your chassis and guards. Fieldens OTR Ltd supplies matched tyre–wheel packages and precision rims to fit UK implements.
Step 4 — Set Inflation Pressure From Load/Speed Tables
Use the manufacturer’s load–inflation tables for the chosen tyre and speed. Set the lowest pressure that safely carries the load at field speed and raise pressure for sustained road work to manage heat. If the required pressure exceeds your ground‑pressure target, choose a wider or higher‑volume tyre.
Consider a central tyre inflation system (CTIS) where you switch between road and field pressures — in our experience it pays back on mixed‑duty fleets by protecting casings and soils.
This image was generated with AI and may not always represent the product or service exactly.
Step 5 — Check Geometry, Legality And Service Factors
Verify diameter and rolling radius for hitch height, gearing and clearance. Check sidewall, chassis and mudguard gaps at full articulation. Confirm track width and stability and ensure brake lines and ABS sensors are clear of the tyre.
For UK road use, confirm axle weights and dimensions meet legal limits. If constraints exist, revisit rim offset or tyre family until everything clears safely.
Step 6 — Validate In The Field And Fine‑Tune
Recheck axle and tyre loads on a weighbridge. Do a footprint test on firm soil or with a film sheet to verify area and shape. After a road/field cycle log hot pressures and sidewall temperatures and adjust within the manufacturer limits.
Build a simple record of load, speed, pressure and outcome. In our experience, this small habit extends tyre life and preserves soil structure.
Worked Example: Sizing A Tandem Spreader
Inputs: 18 t gross laden tandem spreader, four tyres, 60% field/40% road. Target: 80 kPa for wet spring work. Load per tyre: 18 t ÷ 4 = 4.5 t ≈ 44 kN. Required area: 44 ÷ 80 ≈ 0.55 m². Add 10% margin ≈ 0.60 m².
Choose section width 650–710 mm. Footprint length ≈ 0.85–0.95 m. Select a flotation size that delivers ~0.60 m² at ~1.0–1.2 bar at field speed, with the maker’s recommended rim width and suitable offset. Confirm final pressures from the tyre tables before fitting.
Bespoke Builds, Tyrefill And Partner Brands
Fieldens OTR Ltd manufactures bespoke rims to precise offsets, PCDs and finishes to ensure correct fit and long service life. We supply and assemble complete tyre–wheel packages to your specification.
Where puncture risk threatens uptime, Fieldens Polycoat Tyrefill can keep trailers moving. It adds weight, so recalculate loads and pressures. We work with established tyre brands and build packages for agricultural and industrial duties; contact us to discuss options.
Maintenance For Reliability And Long Service Life
Check pressures cold before work and monitor hot after runs; adjust within table limits. Inspect beads and sidewalls for cuts and leaks. Rotate positions on multi‑axle trailers to even wear and reset pressures for seasonal duties.
Replace tyres with deep cuts, bulges or persistent heat issues; retread only where casings and duty allow. Good care protects both soil and your capital investment.
What Most People Get Wrong
Many assume tyre width alone solves compaction. In practice you need sufficient footprint area (width × length) at the correct pressure, plus correct rim width and axle load distribution. Ignoring one of these elements undermines the others.
When This Doesn’t Apply
This method does not apply to rubber‑tracked machines, specialist low‑ground‑pressure systems designed by OEMs, or very low‑speed off‑road bogging work where other factors dominate. For such equipment follow the manufacturer’s guidance.
Quick Checklist
- Weighbridge: gross and axle loads laden/unladen
- Tyre count per axle, section width, current rim widths
- Target ground pressure and duty cycle (field vs road %)
- Soil condition and likely load shifts
- Footprint test and log of pressure vs performance
Talk To Us: Data We Need For A Correct Specification
To specify correctly we need vehicle and axle details (laden/unladen), number of tyres per axle and spacing, target ground pressure, duty cycle and speeds, soil conditions, current sizes and clearances. Photos and weighbridge tickets help.
Fieldens OTR Ltd offers on‑site measurement and fitting across the UK. Share your details via our contact page and we will build the right solution for your work.
FAQs
How Do I Choose Between Wide Singles And Duals For A Trailer?
Choose wide singles where space, service access and legal width allow; they simplify track and maintenance. Duals increase area but add complexity and potential tyre‑to‑tyre interaction. Decide on the basis of available track width, legal limits and serviceability.
Is Central Tyre Inflation Worth The Cost For Mixed Road/Field Work?
For fleets that alternate frequently between road and field, CTIS often pays back through reduced tyre wear, lower fuel use and less soil damage. For mainly field or mainly road machines it is less compelling.
Which Measurements Should I Send Fieldens OTR Ltd First?
Send gross vehicle mass, axle weights, tyre sizes and rim widths, photos of mounting clearances, and representative weighbridge tickets. These let us recommend a viable tyre–wheel package quickly.
How Do I Validate My Footprint After Fitting New Tyres?
Use a film or cardboard test on firm soil, or weighbridge checks to confirm axle splits. Compare measured area and pressure against your calculated target and adjust within tyre maker limits.