NZ TYRE PRESSURE GUIDE
The complete guide to understanding, calculating, and optimising tyre pressure
Typical pressure ranges by vehicle type. For precise PSI, use the Calculator tab.
These tables show % of maximum load capacity supported at each PSI. Find the lowest PSI that supports your load percentage, then add 2-3 PSI safety margin.
Note on ply ratings: the Load Range letter (C, D, E, F) reliably sets the maximum pressure, but the ply number does not describe capacity. Across our workshop records 6-ply tyres span 800–1,150 kg and 8-ply span 560–1,500 kg — every 6-ply tyre we measured carries more than the weakest 8-ply. Always use the load index on the sidewall.
| PSI | % Capacity |
|---|---|
| 26 | 71% |
| 29 | 79% |
| 32 | 87% |
| 35 | 95% |
| 36 | 100% |
| PSI | % Capacity |
|---|---|
| 26 | 61% |
| 29 | 68% |
| 32 | 75% |
| 36 | 85% |
| 40 | 93% |
| 42 | 100% |
| PSI | % Capacity |
|---|---|
| 26 | 52% |
| 30 | 60% |
| 35 | 70% |
| 40 | 80% |
| 45 | 90% |
| 50 | 100% |
| PSI | % Capacity |
|---|---|
| 26 | 40% |
| 35 | 54% |
| 45 | 69% |
| 55 | 85% |
| 65 | 100% |
| PSI | % Capacity |
|---|---|
| 35 | 44% |
| 50 | 63% |
| 65 | 81% |
| 80 | 100% |
| PSI | % Capacity |
|---|---|
| 35 | 37% |
| 50 | 53% |
| 65 | 68% |
| 80 | 84% |
| 95 | 100% |
🇳🇿 Powered by NZ Vehicle Fleet Database — Select your vehicle for GVM-based pressure recommendations.
Tyre pressure is measured in PSI (Pounds per Square Inch) or kPa (Kilopascals). The correct pressure ensures optimal grip, even wear, fuel efficiency, and safety.
📍 WHERE TO FIND YOUR RECOMMENDED PRESSURE
Understanding how to calculate the correct pressure for your load ensures safety and optimal tyre life.
📊 CALCULATION STEPS
- Find your axle weights – weigh loaded, or use 60/40 front/rear split
- Divide by tyres – front axle ÷ 2 (or 4 for duals) = load per tyre
- Find load index kg – use reference table below
- Apply formula – (actual ÷ max) × max PSI
- Add safety margin – multiply by 1.05-1.10
⚠️ IMPORTANT RULES
- Never exceed tyre's maximum pressure
- Never go below pressure for your actual load
- Front/rear may differ due to weight distribution
- Add 4-7 PSI to rear when towing
- Dual rear tyres: each tyre carries half the axle load
The "divide by 3" rule gives you a safe minimum starting pressure for off-road. This accounts for the increased footprint needed for soft terrain while maintaining enough pressure to protect your rims.
Different terrains require different pressures. Lower pressure increases the tyre's footprint for better flotation. Always carry a compressor to re-inflate after off-road driving.
Towing requires careful pressure management. The tow ball weight transfers load to your rear axle, and caravan tyres need to be set based on actual trailer weight.
🚗 TOW VEHICLE ADJUSTMENTS
- Rear tyres: Increase 4-7 PSI when towing
- Front tyres: May stay same or decrease slightly
- Dual rear axle: Less increase needed per tyre
- Verify level stance — adjust if rear sags
🏕️ CARAVAN/TRAILER FORMULA
Example: 50 PSI max, 900kg max, 1600kg GTM, 4 tyres → (50÷900)×(1600÷4) = 22 PSI
🛞 AXLE CONFIGURATIONS
SINGLE AXLE
2 tyres total (1 per side)
- Each tyre carries 50% of GTM
- Higher pressure per tyre needed
- Common on small trailers, boat trailers
TANDEM AXLE
4 tyres total (2 per side, 2 axles)
- Each tyre carries 25% of GTM
- Lower pressure per tyre
- Common on caravans, large trailers
SUPER SINGLE / WIDE SINGLE
4 tyres on same axle (2 per side)
- Common on heavy trailers, trucks
- Each tyre still carries 25% of axle load
- May have inner/outer pressure differences
Tyre pressure changes with temperature and altitude. Understanding these effects helps you maintain optimal pressure.
☀️ HOT TYRES
- Expect +10-20 PSI above cold reading
- NEVER reduce hot tyre pressure
- If hot reading is at/below recommended = severely underinflated
❄️ COLD WEATHER
- Pressure drops as temperature drops
- Check more frequently in winter
- TPMS may trigger false alarms on cold mornings
Wrong tyre pressure affects safety, wear, fuel economy, and handling.
📉 UNDERINFLATION
- Wear: Both outer edges wear faster — one edge alone means alignment, not pressure
- Fuel: -0.2% to -0.3% per 1 PSI drop
- Stopping: Longer wet braking distances
- Heat: The casing flexes further, runs hotter, and heat is what degrades rubber and bonding
📈 OVERINFLATION
- Wear: Centre tread wears faster
- Contact: Reduced contact patch
- Ride: Harsher, more uncomfortable
- Impact: Rim damage from bumps
VISUAL WEAR PATTERNS
Bar heights are real tread depths measured across four tyres from our workshop programme. Percentages are how often each pattern appears across 1,149 measured tyres.
Fix: add air
Keep it there
Fix: let air out
Air will not fix this
The four patterns above, shown on real tyres measured in our workshop. Each carries its actual tread readings across the width and a note from the inspection. These are the same shapes the diagram shows — this is what they look like on the road.
Complete reference tables for load index (50-160), all speed ratings, and pressure conversions.
LOAD INDEX TABLE (50-160)
| LI | kg | LI | kg | LI | kg | LI | kg | LI | kg | LI | kg |
|---|---|---|---|---|---|---|---|---|---|---|---|
| 50 | 190 | 60 | 250 | 70 | 335 | 80 | 450 | 90 | 600 | 100 | 800 |
| 51 | 195 | 61 | 257 | 71 | 345 | 81 | 462 | 91 | 615 | 101 | 825 |
| 52 | 200 | 62 | 265 | 72 | 355 | 82 | 475 | 92 | 630 | 102 | 850 |
| 53 | 206 | 63 | 272 | 73 | 365 | 83 | 487 | 93 | 650 | 103 | 875 |
| 54 | 212 | 64 | 280 | 74 | 375 | 84 | 500 | 94 | 670 | 104 | 900 |
| 55 | 218 | 65 | 290 | 75 | 387 | 85 | 515 | 95 | 690 | 105 | 925 |
| 56 | 224 | 66 | 300 | 76 | 400 | 86 | 530 | 96 | 710 | 106 | 950 |
| 57 | 230 | 67 | 307 | 77 | 412 | 87 | 545 | 97 | 730 | 107 | 975 |
| 58 | 236 | 68 | 315 | 78 | 425 | 88 | 560 | 98 | 750 | 108 | 1000 |
| 59 | 243 | 69 | 325 | 79 | 437 | 89 | 580 | 99 | 775 | 109 | 1030 |
| CONTINUED... | |||||||||||
| 110 | 1060 | 120 | 1400 | 130 | 1900 | 140 | 2500 | 150 | 3350 | 160 | 4500 |
| 111 | 1090 | 121 | 1450 | 131 | 1950 | 141 | 2575 | 151 | 3450 | -- | -- |
| 112 | 1120 | 122 | 1500 | 132 | 2000 | 142 | 2650 | 152 | 3550 | -- | -- |
| 113 | 1150 | 123 | 1550 | 133 | 2060 | 143 | 2725 | 153 | 3650 | -- | -- |
| 114 | 1180 | 124 | 1600 | 134 | 2120 | 144 | 2800 | 154 | 3750 | -- | -- |
| 115 | 1215 | 125 | 1650 | 135 | 2180 | 145 | 2900 | 155 | 3875 | -- | -- |
| 116 | 1250 | 126 | 1700 | 136 | 2240 | 146 | 3000 | 156 | 4000 | -- | -- |
| 117 | 1285 | 127 | 1750 | 137 | 2300 | 147 | 3075 | 157 | 4125 | -- | -- |
| 118 | 1320 | 128 | 1800 | 138 | 2360 | 148 | 3150 | 158 | 4250 | -- | -- |
| 119 | 1360 | 129 | 1850 | 139 | 2430 | 149 | 3250 | 159 | 4375 | -- | -- |
SPEED RATING TABLE (ALL RATINGS)
| Rating | km/h | Rating | km/h | Rating | km/h | Rating | km/h |
|---|---|---|---|---|---|---|---|
| A1 | 5 | E | 70 | M | 130 | V | 240 |
| A2 | 10 | F | 80 | N | 140 | Z | 240+ |
| A3 | 15 | G | 90 | P | 150 | W | 270 |
| A4 | 20 | J | 100 | Q | 160 | Y | 300 |
| A5 | 25 | K | 110 | R | 170 | (Y) | 300+ |
| B | 50 | L | 120 | S | 180 | -- | -- |
| C | 60 | -- | -- | T | 190 | -- | -- |
| D | 65 | -- | -- | U | 200 | -- | -- |
| -- | -- | -- | -- | H | 210 | -- | -- |
PSI TO KPA CONVERSION (COMPREHENSIVE)
| PSI | kPa | PSI | kPa | PSI | kPa | PSI | kPa | PSI | kPa |
|---|---|---|---|---|---|---|---|---|---|
| 10 | 69 | 20 | 138 | 30 | 207 | 40 | 276 | 50 | 345 |
| 11 | 76 | 21 | 145 | 31 | 214 | 41 | 283 | 55 | 379 |
| 12 | 83 | 22 | 152 | 32 | 221 | 42 | 290 | 60 | 414 |
| 13 | 90 | 23 | 159 | 33 | 228 | 43 | 296 | 65 | 448 |
| 14 | 97 | 24 | 165 | 34 | 234 | 44 | 303 | 70 | 483 |
| 15 | 103 | 25 | 172 | 35 | 241 | 45 | 310 | 75 | 517 |
| 16 | 110 | 26 | 179 | 36 | 248 | 46 | 317 | 80 | 552 |
| 17 | 117 | 27 | 186 | 37 | 255 | 47 | 324 | 85 | 586 |
| 18 | 124 | 28 | 193 | 38 | 262 | 48 | 331 | 90 | 621 |
| 19 | 131 | 29 | 200 | 39 | 269 | 49 | 338 | 100 | 689 |
Calculate your optimal tyre pressure based on vehicle weight, tyre specifications, terrain, and towing configuration.
Most tyre pressure advice is borrowed from overseas surveys. The figures in this section are not — they come from tyres we measured ourselves, here, one at a time.
📏 WHAT WE MEASURED
- 1,550 documented tyre inspections
- 39,000+ workshop photographs, all taken in-house
- 1,149 tyres with a full tread profile across the width
- Four depth readings per tyre — enough to recover the shape of the wear, not just how much is left
📊 WHAT WE FOUND
- 26.6% worn on both shoulders — run soft
- 14.8% worn down the centre — run hard
- 13.8% worn on one side only — alignment, not pressure
- Only 44.7% had worn evenly across the tread
- Utes are the opposite problem. On passenger tyres under-inflation dominates. On light-truck tyres it reverses hard — 40% over-inflated against 6% under — because a load-rated tyre set for a full load spends most of its life empty.
- One-sided wear is the expensive one. It fails an inspection 70% of the time against 45% for pressure faults, and throws away 2.5 mm of usable tread per tyre. No pressure setting fixes it.
- You genuinely cannot see low pressure. Of the tyres whose tread showed a clear under-inflation pattern, 68% had nothing noted by eye at inspection.
READ THE FULL RESEARCH
Our research is descriptive analysis of one workshop’s records. It is not a representative sample of the national fleet, and it is not a substitute for a warrant of fitness inspection.
Every table on this page traces to a published standard, and every wear figure to our own measured data. Here is where each comes from. External links checked July 2026.
STANDARDS & REGULATIONS
Where the load, pressure and speed tables come from, and the rules a New Zealand tyre must meet.
-
ETRTO — European Tyre and Rim Technical Organisation
The standards body whose load-and-inflation tables the calculator and reference charts on this page are built from.
-
NZTA VIRM: In-service WoF & CoF — 10-1 Tyres and wheels
The official Warrant of Fitness inspection requirements for tyres, including tread depth, load rating and speed rating.
-
NZ Transport Agency — Tyres and wheels
Plain-language guidance from Waka Kotahi covering the Land Transport Rule: Tyres and Wheels 2001.
OUR OWN RESEARCH
The wear-pattern and inflation figures on this page come from our own workshop programme. The full analysis is here.
-
The Tyre Dispatch Research Hublink coming soon
Every report we have published, with live programme totals.
-
The First 1,500 Inspections — full reportlink coming soon
Our complete findings on tread depth, wear, certification and country of origin.
-
The Tyre Pressure Report — over and under-inflationlink coming soon
Where the 26.6% / 14.8% / 13.8% wear figures on this page are derived and explained in full.
REFERENCES
The external standards and studies referenced in this guide.
-
ICCT — Opportunities to Improve Tire Energy Efficiency
The International Council on Clean Transportation on rolling resistance and its effect on fuel economy.
-
BTMA — Tyres and the environment: CO₂ emissions
The British Tyre Manufacturers’ Association on how under-inflation wastes fuel, tyres and CO₂.
-
Michelin — What is rolling resistance?
A manufacturer’s explanation of how inflation pressure drives rolling resistance and fuel use.
-
TyreSafe — UK tyre safety organisation
Campaigns and survey data on tyre pressure, tread depth and road safety.
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