NZ TYRE PRESSURE GUIDE
The complete guide to understanding, calculating, and optimising tyre pressure
32-36 PSI
Typical Passenger
35-80 PSI
Light Truck Range
10-20 PSI
Off-Road Range
±1 PSI / 5°C
Temperature Effect
UNDERSTANDING TYRE PRESSURE
▼
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.
💡 The Key Principle: It's the air volume inside the tyre that supports the vehicle's weight, not the pressure itself. Larger tyres need less pressure to support the same weight because they contain more air volume.
🔄 INTERACTIVE PRESSURE CONVERTER
35
PSI
=
241
kPa
=
2.41
BAR
📍 WHERE TO FIND YOUR RECOMMENDED PRESSURE
DRIVER'S DOOR JAMB
Most common location - on the B-pillar
FUEL FILLER FLAP
Inside the petrol cap door
GLOVEBOX
On the door or inside lid
CENTRE CONSOLE
Inside the console door
ENGINE COMPARTMENT
On strut tower or firewall
OWNER'S MANUAL
Full specifications & laden pressures
⚠️ Important: The sidewall shows MAXIMUM pressure, not the recommended pressure for your vehicle. Always use the placard or manual values.
COLD
Always Check When Cold
MONTHLY
Check Frequency
1-2 PSI
Natural Loss/Month
+10-20 PSI
Hot vs Cold Rise
LOAD CALCULATIONS & FORMULAS
▼
Understanding how to calculate the correct pressure for your load ensures safety and optimal tyre life.
📊 INTERACTIVE LOAD/PRESSURE CALCULATOR
FORMULA: (Actual Load ÷ Max Load) × Max PSI × 1.1 Safety Margin
(500 ÷ 615) × 44 × 1.1 =
39
PSI RECOMMENDED (269 kPa)
📊 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
🏔️ OFF-ROAD PRESSURE STARTING POINT
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.
÷ 3 =
12
MIN OFF-ROAD PSI
--
SAND (MIN÷1)
--
MUD (MIN×1.5)
--
ROCK (MIN×1.3)
💡 Example: Highway pressure 36 PSI → 36÷3 = 12 PSI minimum for soft sand. For rocky terrain, use 12×1.3 = ~16 PSI for rim protection. Always re-inflate before returning to sealed roads!
📊 Load Range (LT Tyres): C = 6-ply/50 PSI | D = 8-ply/65 PSI | E = 10-ply/80 PSI | F = 12-ply/95 PSI | G = 14-ply/110 PSI
TERRAIN PRESSURE GUIDE
▼
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.
⚠️ Safety Rules: Never drive at highway speeds with lowered pressures. Re-inflate before returning to sealed roads. Below 10 PSI: risk of bead separation on sharp turns.
SAND / BEACH
10-20 PSI
Recommended
Soft Sand10-15 PSI
Firm Sand18-20 PSI
Max Speed20-35 km/h
💡 Tips: Lower = larger footprint = less sinking. Maintain momentum. Avoid sharp turns at low pressures.
MUD
16-30 PSI
Varies
Slippery/Firm Base26-30 PSI
Deep Gooey Mud16-22 PSI
Max Speed20 km/h
💡 Tips: Firm base = higher pressure to cut through. Deep mud = lower for flotation.
ROCKS
14-26 PSI
Recommended
Technical Rocks14-18 PSI
Rocky Trail20-26 PSI
Min (rim safe)14 PSI
💡 Tips: Lower lets tyre mould around rocks. Too low = rim damage risk.
GRAVEL
26-32 PSI
Recommended
Good Gravel28-32 PSI
Corrugations24-28 PSI
Max Speed65-70 km/h
💡 Tips: Slightly lower absorbs vibrations and reduces stone damage.
HIGHWAY
32-40 PSI
As Per Placard
Passenger Cars32-36 PSI
SUVs / Utes32-40 PSI
LT (loaded)50-80 PSI
💡 Tips: Always use manufacturer recommended pressure. Check cold.
TOWING & CARAVAN PRESSURES
▼
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
(MAX PSI ÷ MAX LOAD) × (GTM ÷ TYRES) = PSI
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
⚠️ Dual Axle Warning: Don't assume equal distribution! Moving cargo can shift weight significantly between axles. Calculate for the heavier axle.
50-65 PSI
Highway Towing
30-35 PSI
Gravel Roads
15-18 PSI
Sand/Beach
+4 PSI
Hot Rise Check
TEMPERATURE & ALTITUDE EFFECTS
▼
Tyre pressure changes with temperature and altitude. Understanding these effects helps you maintain optimal pressure.
🌡️ TEMPERATURE PRESSURE CHANGE
±1 PSI per 5.5°C change
-2.7
PSI CHANGE
→
32.3
EXPECTED PSI
☀️ 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
⛰️ Altitude Effect: Gauge pressure increases ~0.5 PSI per 1,000 ft elevation. Temperature drop often offsets this. Set pressure at destination altitude after overnight cooling.
UNDER & OVER INFLATION EFFECTS
▼
Wrong tyre pressure affects safety, wear, fuel economy, and handling.
📉 UNDERINFLATION
- Wear: Outer edges wear faster
- Fuel: -0.2% to -0.3% per 1 PSI drop
- Stopping: +10-20% distance increase
- Blowout: 90% of blowouts from underinflation
7 PSI underinflation =
~8% MORE FUEL
📈 OVERINFLATION
- Wear: Centre tread wears faster
- Contact: Reduced contact patch
- Ride: Harsher, more uncomfortable
- Impact: Rim damage from bumps
VISUAL WEAR PATTERNS
EDGE WEAR
UNDERINFLATED
EVEN WEAR
CORRECT
CENTRE WEAR
OVERINFLATED
REFERENCE TABLES
▼
Complete reference tables for load index (50-160), all speed ratings, and pressure conversions.
LOAD INDEX TABLE (50-160)
LOAD INDEX → MAX WEIGHT (KG)
| 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)
SPEED RATING → MAX SPEED (KM/H)
| 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 | -- | -- | H | 210 | -- | -- |
PSI TO KPA CONVERSION (COMPREHENSIVE)
PSI → kPa (10-100 PSI)
| 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 |
📐 Quick Conversion: PSI × 6.895 = kPa | kPa × 0.145 = PSI | PSI × 0.0689 = BAR
PRESSURE CALCULATOR
▼
Calculate your optimal tyre pressure based on vehicle weight, tyre specifications, terrain, and towing configuration.
📝 YOUR DETAILS
🚗 VEHICLE TYPE
🛞 VEHICLE REAR AXLE
Dual = 2 tyres per side on rear axle (trucks, motorhomes)
⚖️ VEHICLE WEIGHT (LOADED)
🛞 TYRE SPECIFICATIONS
🏔️ TERRAIN
🚐 TOWING
✓
I'm towing a trailer/caravan
TRAILER/CARAVAN AXLE CONFIG
Single = 2 tyres | Tandem = 4 tyres (2 axles) | 4 on Axle = 4 tyres on single axle (heavy duty)
📊 RECOMMENDED PRESSURES
32
FL
32
FR
32
RL
32
RR
VEHICLE
🚐
45
TL
45
TR
TRAILER
32
Front PSI
32
Rear PSI
221
Front kPa
221
Rear kPa
⚠️ Disclaimer: This calculator provides estimates. Always verify against manufacturer recommendations and tyre load/inflation charts. Check pressure when cold.
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