where K(front) = 0.069 bar/100 kg · K(rear) = 0.103 bar/100 kg · K(sand/mud rear) = 0.069 bar/100 kg
Base pressures for each terrain/size combination are set at medium load (350 kg) — a reasonable midpoint for a two-person expedition with full gear. They are derived from tyre manufacturer load-inflation tables (LT 10PR load range), cross-referenced with practitioner guidance for each terrain type.
The 265/70R16 highway baseline of 2.41 bar aligns with the Maxxis AT811 LT specification for the vehicle's front axle load (~1,100 kg at kerb weight + 45% of payload). Rear is set 0.14 bar higher to account for the LC76's rear-heavy load distribution.
The calculator applies a linear load correction from the 350 kg baseline. For every 100 kg above or below baseline: front axle adds/subtracts 0.069 bar; rear axle adds/subtracts 0.103 bar. The rear coefficient is higher because the LC76's rear axle carries a disproportionate share of expedition load (fridge, water, fuel, recovery gear).
On sand and mud the load coefficient is halved — contact patch geometry is the primary variable in soft terrain, not load support. Adding pressure to carry load on sand defeats the purpose of deflation.
Larger diameter and wider section tyres achieve an equivalent contact patch at lower absolute pressure. The 265/75R16 runs ~0.07 bar lower than the 70-series equivalent; the 285/75R16 runs ~0.14 bar lower. This reflects the increased tyre volume — the same mass of air in a larger casing produces lower pressure while maintaining equivalent load support.
Wider tyres (285) benefit from additional deflation on sand because a wider footprint spreads load over more surface area, reducing sinkage independently of pressure.
Highway: Maximise pressure for fuel economy, tread life, and steering precision.
Gravel: Reduce ~0.35 bar to absorb stone impacts and widen contact patch.
Corrugated: Reduce ~0.62 bar — softer tyre reduces wheel bounce and chassis vibration transmission.
Sand: Deflate significantly (~50%) for maximum footprint. Speed limit 20 km/h.
Mud: Balance between flotation and self-cleaning tread (~40% reduction).
Rock: Moderate reduction for rock conformity; maintain enough pressure to protect sidewalls from cuts.
Comparison of the three tyre sizes relevant to the LC76 upgrade path. Current fitment is 265/70R16. The 265/75R16 is a sidewall-only upgrade; the 285/75R16 adds both width and sidewall height. All three are available in LT (Light Truck) 10-ply load range.
Values in bar. F = Front axle · R = Rear axle.
| Terrain | 265/70R16 F | 265/70R16 R | 265/75R16 F | 265/75R16 R | 285/75R16 F | 285/75R16 R |
|---|---|---|---|---|---|---|
| Highway | 2.41 | 2.55 | 2.34 | 2.48 | 2.28 | 2.41 |
| Gravel | 2.07 | 2.21 | 2.00 | 2.14 | 1.93 | 2.07 |
| Corrugated | 1.79 | 1.93 | 1.72 | 1.86 | 1.66 | 1.79 |
| Sand | 1.10 | 1.24 | 0.97 | 1.10 | 0.83 | 0.97 |
| Mud | 1.38 | 1.52 | 1.24 | 1.38 | 1.17 | 1.31 |
| Rock | 1.52 | 1.65 | 1.38 | 1.52 | 1.24 | 1.38 |
- Proven fit — no clearance issues
- Speedo accurate
- Maxxis AT811 available locally
- Lower sidewall = more rim strike risk
- Good all-round for this build
- Same width — no clearance issues
- +13 mm more sidewall protection
- +2.7% speedo correction needed
- Fits existing 7–8.5" rims
- Best balance for remote Africa travel
- Paul Marsh suggested this upgrade
- +28 mm sidewall — best protection
- Wider contact patch in sand
- Must verify wheel arch clearance
- Check rub on full lock + articulation
- +6.7% speedo correction needed
- May require rim upgrade to 8–9"
Clearance check (285/75R16): Before committing, turn full lock both ways on full articulation and check clearance to wheel arch, brake lines, and front diff. The HZJ76R has reasonable clearance but 285-width can be tight. Snyman 4×4 assessment (May 2026) is the right time to confirm this.