Tyre pressure — what to run, and how to tell what yours has been doing
Where to find your number, why it only counts when the tyres are cold, and how to read the wear across the tread to see what your pressure has actually been. Load, towing, terrain, temperature and TPMS — with wear figures from 1,149 tyres we measured ourselves, four points across each tread.
Start from the placard in your driver's door jamb — not the number moulded on the tyre, which is the tyre's maximum rather than your vehicle's setting. Then, on a car or SUV running standard tyres, we would add a couple of PSI to it. Check it cold, with a gauge, once a month, and do the spare while you are there.
- Why add a couple: nearly twice as many tyres come through our workshop worn from running soft as from running hard, and NZ placards on SUVs often read 30–34 PSI. What we actually tell customers.
- Cold means cold: before driving, or three hours after. A warm tyre reads 10–20 PSI high and never needs air let out of it.
- You cannot see it: of the tyres we measured showing clear under-inflation wear, 68% had nothing noted by eye — trained people, wheel off the car.
- The tread tells the story: both shoulders worn means soft, a worn centre strip means hard, one side only means alignment and no pressure setting will fix it.
- Utes are the opposite problem: load-rated tyres set for a full load spend their lives empty — 40% of the light-truck tyres we measure are over-inflated, against 6% under.
In this guide
Where to find your recommended pressure
The number you want is on a placard on the vehicle, not on the tyre. The vehicle manufacturer sets it from the car's weight, its weight distribution and the tyre size it was designed around. On most New Zealand vehicles it is a sticker in the driver's door jamb.
The usual place — open the door and look at the B-pillar or the door frame itself.
Inside the fuel door, often on European and Japanese imports.
On the inside of the lid or the back wall.
Inside the console lid on some models.
On a strut tower or the firewall, mostly on older vehicles.
The full specification, including the laden pressures the placard often leaves off.
The figure moulded into the tyre — "MAX PRESS 51 PSI" or similar — is the maximum the casing is rated to hold at its maximum load. It is a limit, not a recommendation. Inflating a family car to the sidewall maximum will wear a strip down the middle of the tread and make the ride noticeably worse. Use the placard.
The placard is the manufacturer's baseline and it is the right place to start. In practice, on cars and SUVs running standard tyres — highway, all-terrain, high performance, anything that is not a load-rated light-truck tyre — we suggest adding a couple of PSI to whatever it says, then watching the wear.
Why. Placard figures are set for a lightly loaded vehicle, and are weighted towards ride comfort and the manufacturer's own economy testing. Real cars carry people and gear. Tyres also lose 1–2 PSI a month on their own, so setting a little high means you spend more of the month near correct instead of under it. And it matches what we measure: 26.6% of the tyres we profile are worn from running soft against 14.8% worn from running hard — under-inflation is close to twice as common.
A worked answer. If someone rings and says they have an ordinary SUV on standard tyres, we will generally say 38–40 PSI and to keep an eye on it — even where the placard reads 30–34, which a lot of SUVs and utes here do. Set it, run it, then look at the tread: shoulders going means add more, a centre strip going means you have gone too far. The tyre will tell you within a few thousand kilometres.
- Never go above the tyre's maximum — the figure moulded on the sidewall. On a normal car that is 44–51 PSI, so 38–40 is nowhere near it, but check.
- Light-truck tyres on an empty ute or van are the opposite problem. Do not add to those — if anything they need less. See why.
- Ride comfort is the trade. A few PSI up is firmer over sharp bumps. On rough rural roads some people prefer to stay closer to the placard, and that is a legitimate choice.
- This is our workshop opinion, not a standard. It comes from what we measure on New Zealand vehicles; we cannot tell you how much of it is specific to our roads and our fleet rather than universal. The placard figure is what the vehicle was certified with.
Many placards list a normal and a laden or full load pressure. Use the normal figure for everyday driving and only move to the laden figure when the vehicle is actually loaded — a full boot and a full car, or a trailer on the back. Running laden pressures empty is its own problem: see utes, vans and light trucks.
Check them cold, with a gauge, once a month
Every published pressure is a cold pressure. Driving heats the air inside the tyre and the pressure climbs with it — a tyre that has been on the motorway for half an hour can read 10 to 20 PSI above its cold figure. That reading is not wrong, it is just not the number the placard is talking about.
- Cold means before you driveFirst thing in the morning is ideal. Otherwise leave the vehicle at least three hours after driving. A trip to the servo and back is enough to make the reading useless — if the nearest air hose is more than a kilometre away, set the pressures a little high and re-check them cold at home.
- Never let air out of a hot tyreThe pressure is high because the air is hot; bleed it down to the placard figure and the tyre will be badly under-inflated once it cools. If a hot tyre reads at or below the recommended cold pressure, it is severely under-inflated and needs air now.
- Use a gauge, not a look and a kickA tyre can be several PSI low and look completely normal, especially a modern low-profile one with a stiff sidewall. A pencil gauge costs a few dollars; the good digital ones are under $30.
- Do all fiveFront and rear are often different — check the placard rather than assuming. The spare is the tyre nobody checks and the one you will be relying on at the side of the road.
- Once a month, and before any big tripA healthy tyre loses 1–2 PSI a month through the rubber itself, before you count temperature changes or a slow leak.
A soft tyre wears both shoulders down while the centre keeps its depth — obvious once you measure across the tread, almost nothing to look at. We found that pattern on 333 tyres, and on 227 of them (68%) the inspector had noted nothing unusual by eye. Trained people, wheel off the car, tyre in their hands, and two thirds of the time low pressure simply does not look like anything until it has already cost you tread. That is the whole argument for a gauge.
Reading the wear: what the tread tells you about your pressure
You cannot see 4 PSI. You can see what 4 PSI did over 20,000 km. Measure the depth at four points across the tread — outer shoulder, both centre grooves, inner shoulder — and the shape of the wear tells you what the pressure has been doing.
That is exactly what we do to every tyre that comes through the workshop. Across 1,149 tyres with a full profile measured, this is how it lands:
26.6% of tyres
Run soft. The casing flexes and the edges carry the load while the centre lifts away from the road.
Fix: add air.
44.7% of tyres
Correct pressure, and usually rotated on schedule. Depth within a few tenths of a millimetre right across.
Fix: nothing. Keep doing it.
14.8% of tyres
Run hard. The tyre crowns and rides on the middle of the tread while the shoulders barely touch.
Fix: let air out.
13.8% of tyres
Not pressure at all. A steady gradient from one edge to the other is camber or toe.
Fix: wheel alignment.
Both shoulders worn evenly is pressure. One shoulder worn and the other fine is not. No pressure setting will fix a camber or toe fault — and it is the more expensive fault of the two. In our programme, one-sided tyres fail an inspection 70% of the time against 45% for pressure faults, and they throw away 2.5 mm of usable tread per tyre against 1.6 mm. The fault also does the same thing to the replacement tyre, so it is worth chasing rather than living with.
Eight tyres from our workshop, with their readings
Each photograph is a tyre we measured, with the four depths across its tread and the note from the inspection. The numbers read outer shoulder first, then the two centre grooves, then the inner shoulder.
Run soft — both shoulders gone
Correct — even right across
Run hard — the centre gone first
Not pressure — alignment
All eight photographed in our workshop, depths measured by hand with a gauge at four points across the tread. Entry numbers refer to our inspection database. Photographs © Taylor Houghton.
How tyre pressure actually works
It is the air that carries the car, not the tyre. The casing is a container; the load is supported by the volume of air inside it at a given pressure. That single idea explains most of what follows — including why a bigger tyre needs less pressure to carry the same weight, because it holds more air.
It also explains the failure mode. Take air out and the casing has to flex further on every rotation to carry the same load. Flexing generates heat, and heat is what degrades rubber and the bonds between the plies. An under-inflated tyre does not fail because it is soft; it fails because it has been hot.
PSI, kPa and bar
Three units for the same thing. New Zealand placards usually give kPa, most gauges here read PSI, and European vehicles often quote bar.
| PSI | kPa | bar | Where you see it |
|---|---|---|---|
| 26 | 180 | 1.80 | Small car, unladen |
| 29 | 200 | 2.00 | Light passenger |
| 32 | 220 | 2.20 | Common car front |
| 35 | 241 | 2.41 | The most common NZ passenger figure |
| 36 | 248 | 2.48 | Standard-load maximum |
| 38 | 262 | 2.62 | SUV, loaded car |
| 40 | 276 | 2.76 | Ute, light load |
| 42 | 290 | 2.90 | XL / reinforced maximum |
| 50 | 345 | 3.45 | Load range C, 6-ply |
| 65 | 448 | 4.48 | Load range D, 8-ply |
| 80 | 552 | 5.52 | Load range E, 10-ply |
1 PSI = 6.895 kPa = 0.0689 bar. To go from PSI to kPa multiply by 6.9; the other way, divide. The quick pressure chart has the full conversion run.
Two tyres carrying the same 500 kg: the larger one contains more air, so it needs fewer PSI to develop the same supporting force. This is why fitting a taller or wider tyre usually means the placard pressure no longer applies exactly, and why the pressure calculator asks for the load index rather than just the vehicle.
Load and pressure: the relationship the placard is hiding
The placard figure is the manufacturer's answer for a normally loaded vehicle on the original tyre size. Underneath it sits a standard table — the ETRTO load-and-inflation tables — which say how much weight a given tyre carries at a given pressure. Every placard number in the world is derived from one.
You need the table itself when the vehicle is not normal: a different tyre size, a heavy or permanently empty load, a trailer, or a light-truck tyre on a passenger vehicle.
The load range letter sets your ceiling
On light-truck tyres a letter marks the casing's rating, and with it the maximum pressure.
| Load range | Also called | Maximum pressure | Typically on |
|---|---|---|---|
| SL | Standard load | 36 PSI / 248 kPa | Ordinary passenger tyres |
| XL | Extra load, reinforced | 42 PSI / 290 kPa | Heavier cars, many SUVs |
| C | 6-ply rating | 50 PSI / 345 kPa | Vans, light commercial |
| D | 8-ply rating | 65 PSI / 448 kPa | Utes, 4WDs, trailers |
| E | 10-ply rating | 80 PSI / 552 kPa | Heavy utes, light trucks |
| F | 12-ply rating | 95 PSI / 655 kPa | Commercial |
The load range letter reliably sets the maximum pressure. The ply rating attached to it does not describe how much the tyre carries. Across our own 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. If you want to know what a tyre carries, read the load index on the sidewall, not the ply rating.
What percentage of its capacity are you using?
These are the ETRTO figures: the share of the tyre's maximum load it will support at each pressure. Find the lowest pressure that covers your actual load, then add two or three PSI of margin.
| Pressure | SL (max 36) | XL (max 42) | C (max 50) | D (max 65) | E (max 80) |
|---|---|---|---|---|---|
| 26 PSI | 71% | 61% | 52% | 40% | — |
| 29–30 PSI | 79% | 68% | 60% | — | — |
| 32 PSI | 87% | 75% | — | — | — |
| 35–36 PSI | 95–100% | 85% | 70% | 54% | 44% |
| 40–42 PSI | — | 93–100% | 80% | — | — |
| 45 PSI | — | — | 90% | 69% | — |
| 50 PSI | — | — | 100% | — | 63% |
| 55 PSI | — | — | — | 85% | — |
| 65 PSI | — | — | — | 100% | 81% |
| 80 PSI | — | — | — | — | 100% |
ETRTO inflation data, read against the published tables by Peter "Jadatis", the Dutch tyre pressure researcher whose load-and-inflation spreadsheets are the reference most of the European motorhome and caravan community works from. Our pressure calculator runs this method against your axle weights and load index rather than making you interpolate.
Utes, vans and light trucks run the opposite problem
On passenger cars, under-inflation dominates — people top up rarely and tyres lose air slowly. On light-truck tyres it reverses hard, and the reason is structural rather than careless.
A load-rated tyre is built to be inflated hard because it expects weight. The pressure that suits a fully loaded ute is far too much for the same ute running empty — which is how most of them spend most of their lives. The result is a strip worn down the middle of a tyre whose shoulders have barely been used.
What to do about it: use the unladen figure on the door placard for everyday driving, and only move up to the laden pressure when there is actually weight in the tray or on the towball. If your placard only gives one number and the vehicle is empty most of the time, work the pressure out from the load tables or the calculator using the weight the vehicle really carries.
If your ute tows a boat every summer and runs empty the rest of the year, treat that as two settings rather than one compromise. Five minutes with a gauge before and after the season is cheaper than a set of tyres worn out down the middle.
Towing and caravans
Hitching a trailer moves weight onto the tow vehicle's rear axle through the tow ball, and it puts the trailer's own weight onto tyres that are often years old and rarely checked. Both ends need setting.
The tow vehicle
- Rear tyres: add 4–7 PSI over your normal setting. The tow-ball download is real weight and it all lands on the back axle.
- Front tyres: usually unchanged. Some manufacturers specify a small reduction to keep the steering weighted.
- Check the stance. If the rear visibly sags with the trailer on, the pressure is not the whole answer — you are near the vehicle's limits and want a weight-distribution hitch.
- Dual rear wheels: less increase per tyre, because four tyres share the axle instead of two.
The trailer or caravan
Trailer tyres get set from the actual weight on them, not from a car placard:
(max PSI ÷ max load) × (GTM ÷ number of tyres) = your pressure
Worked example: a tyre rated 900 kg at 50 PSI, on a caravan with a 1,600 kg gross trailer mass and four tyres. (50 ÷ 900) × (1,600 ÷ 4) = 22 PSI. Add a couple of PSI of margin and check it cold before you leave.
| Configuration | Tyres | Each tyre carries | Common on |
|---|---|---|---|
| Single axle | 2 | 50% of gross trailer mass | Box trailers, small boat trailers |
| Tandem axle | 4 | 25% of gross trailer mass | Caravans, larger trailers |
| Dual / twin fitment | 4 on one axle | 25% of the axle load | Heavy trailers, light trucks |
Load in a trailer moves, and a badly packed caravan can put far more on one axle than the other. Set the pressure for the heavier axle. And check the trailer's tyre dates while you are there — trailer tyres almost always age out before they wear out.
Off-road: lower pressure, and how to get back safely
Off the seal the job changes. Letting air out lengthens the contact patch, which spreads the vehicle's weight over more ground — that is flotation on sand, and it is also what lets a tyre mould around rocks instead of bouncing off them. The cost is heat, sidewall exposure and the risk of rolling the tyre off the rim.
| Surface | Typical pressure | Speed limit | Why |
|---|---|---|---|
| Highway | Placard figure | Normal | The setting everything else is measured against. |
| Gravel | 26–32 PSI | 65–70 km/h | A few PSI down absorbs corrugations and reduces stone cutting. Not much lower — gravel punctures sidewalls. |
| Rock | 14–26 PSI | Walking pace | Lower lets the tyre wrap the rock. Too low and the rim takes the hit instead. |
| Mud | 16–30 PSI | 20 km/h | Firm base under the mud: stay higher and cut through. Deep and soft: lower for flotation. |
| Sand | 15–22 PSI | 20–35 km/h | The single biggest factor in whether you get stuck. Lighter vehicles go lower than heavy ones. |
Divide your highway pressure by three for a soft-sand minimum: 36 PSI on the road → around 12 PSI is as low as you should be thinking about. Multiply that minimum by about 1.3 for rock, where rim protection matters more than flotation. Treat these as a floor to work up from, not a target — for beach driving specifically, our beach driving guide has pressures by vehicle weight, which is a better way to do it.
- Air down before you are on the soft stuff, in the car park — not once you are already bogged.
- Never drive at road speed on lowered pressures. Low pressure plus speed builds heat fast and is how tyres come off rims on corners.
- Re-inflate before you get back on the seal. Carry a compressor; it is the difference between a day out and a tow truck.
Below about 12 PSI you are into debeading territory on ordinary rims — the tyre can roll off the wheel on a sharp turn. Beadlock rims and aggressive off-road tyres tolerate it; a standard passenger tyre on a factory rim does not.
Temperature and altitude
Air pressure follows air temperature, and the tyre is a sealed container — so every degree the air outside loses, your tyres lose too. The usual rule of thumb is about 1 PSI for every 5–6 °C, which is roughly 1 PSI per 10 °F.
That rule is only right for a car. It is a simplification of the actual relationship, and the simplification breaks down as the pressure goes up — which matters if you run a ute, a van or a caravan.
The formula the rule of thumb comes from
Pressure and temperature in a fixed volume follow the ideal gas law, and the arithmetic only works in absolute terms — absolute pressure, and temperature in kelvin:
P₂ = (P₁ + 14.7) × (T₂ + 273) ÷ (T₁ + 273) − 14.7
P in PSI on the gauge, T in °C. The 14.7 converts your gauge reading to absolute pressure by adding the atmosphere pressing on the outside of it; the 273 converts °C to kelvin. Do it without those two conversions and the answer comes out badly wrong.
Worked example: 35 PSI set at 20 °C, checked on a 5 °C winter morning. (35 + 14.7) × 278 ÷ 293 − 14.7 = 32.5 PSI. Two and a half PSI gone, and nothing has leaked.
Why the rule of thumb misleads on a ute
The higher the pressure, the more absolute pressure is sitting in the tyre, and the more it moves for the same temperature change. Same 5 °C drop, very different results:
| Your pressure | Lost per 5 °C | Lost overnight (15 °C drop) | 1 PSI is lost every… |
|---|---|---|---|
| 26 PSI — small car | 0.7 PSI | 2.1 PSI | 7.3 °C |
| 32 PSI | 0.8 PSI | 2.4 PSI | 6.4 °C |
| 35 PSI — typical car | 0.9 PSI | 2.5 PSI | 5.9 °C |
| 40 PSI — ute, light load | 0.9 PSI | 2.8 PSI | 5.2 °C |
| 50 PSI — load range C | 1.1 PSI | 3.3 PSI | 4.6 °C |
| 65 PSI — load range D | 1.4 PSI | 4.1 PSI | 3.7 °C |
| 80 PSI — load range E | 1.6 PSI | 4.9 PSI | 3.1 °C |
Calculated from the formula above at a 20 °C baseline, sea level. A caravan on 65 PSI loses pressure roughly twice as fast per degree as the car towing it on 35 — which is why the van's tyres are usually the ones that are down after a cold night.
Hot tyres
- Expect 10–20 PSI above the cold figure after a decent run — that is running heat, on top of any ambient rise.
- Never bleed a hot tyre down to the placard number. It will be badly soft once it cools.
- If a hot tyre reads at or below the recommended cold pressure, it is severely under-inflated. Add air.
- Ambient alone is smaller than people think: 35 PSI set on a 15 °C morning reads about 39 PSI on 40 °C tarmac before the tyre has turned a wheel.
Cold mornings
- Pressure falls with the thermometer, so autumn and winter need checking more often.
- A TPMS light that appears on the first frost and clears after ten minutes is usually real — the tyre genuinely was low when cold.
- Set pressures at the temperature you actually drive in, not in the afternoon sun.
- Tyres set in autumn can be 3–4 PSI down by mid-winter with no leak at all.
Gauge pressure reads about 0.5 PSI higher per 1,000 ft of elevation gained, because a gauge measures against the surrounding air and there is less of it up there — the same 14.7 from the formula gets smaller. Coast to the Desert Road is worth roughly 1 PSI, usually cancelled out by the temperature drop that comes with it. Staying at altitude? Set the pressures there, after the tyres have cooled overnight.
The absolute-pressure method used here and in our temperature adjustment calculator follows the work of Peter "Jadatis", the Dutch tyre pressure researcher who worked the ETRTO load-and-inflation formula into something a driver can actually use. His pressure calculators for cars, motorhomes and caravans are published free, and he answers questions on camperforum.nl. The same work underpins the load section above.
TPMS: the light on the dashboard
A tyre pressure monitoring system watches your pressures for you. There are two kinds and they behave differently:
- Direct TPMS — a battery-powered sensor inside each wheel, usually built into the valve stem, radioing an actual pressure to the car. Accurate, tells you which tyre, and eventually needs new sensors.
- Indirect TPMS — no sensors. The car watches wheel speeds through the ABS and notices when one tyre turns slightly faster than the others because it is soft. Free, but it cannot spot all four going down together, and it has to be reset after you adjust pressures.
| Question | Short answer |
|---|---|
| Is it required for a WOF? | No. TPMS is not part of the NZ tyre inspection requirements, and there is no rule requiring one to be retrofitted. |
| Does the light fail a WOF? | Not on its own — but it may prompt the inspector to check the pressures, and the wear that low pressure causes can fail. |
| Sensor life | Typically 5–7 years. The battery is sealed in, so a flat sensor means a new sensor. |
| New tyres | Tell the fitter you have sensors. They sit on the rim where the tyre lever goes and are easy to damage. |
| Moving to new wheels | Usually yes, if the sensors are compatible with the new rims and are refitted with new service kits. |
| After adjusting pressures | Direct systems normally re-learn within a few minutes of driving. Indirect systems need a reset — often a button or a menu item. |
TPMS warnings are typically set to trigger around 25% below the placard pressure. By the time the light comes on the tyre is already well down, has been running hot for a while, and has been quietly costing you fuel and tread. Treat it as an alarm, not a monthly check — the gauge is still the job.
What our own inspections show
Most tyre pressure advice is borrowed from overseas surveys of what drivers say they do. The figures on this page are not. They come from tyres we measured ourselves, here, one at a time.
- 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
- 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
Three things the data changed our minds about
- Utes are the opposite problemOn 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 oneIt fails an inspection 70% of the time against 45% for pressure faults, and throws away 2.5 mm of usable tread per tyre against 1.6 mm. No pressure setting fixes it.
- You genuinely cannot see low pressureOf the tyres whose tread showed a clear under-inflation pattern, 68% had nothing noted by eye at inspection.
Figures are a snapshot taken 26 July 2026 and will move as the programme grows. This 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.
Common questions about tyre pressure
Everything we get asked about pressure, TPMS and what a warrant inspector does and does not look at.
What's the difference between PSI, bar, and kPa on tyres?
These are just three different units for measuring the same thing — air pressure. You'll see all three on tyre sidewalls, pressure gauges, and door placards depending on the manufacturer and country of origin:
| Unit | Full Name | Used By | 1 bar = |
|---|---|---|---|
| PSI | Pounds per Square Inch | NZ, Australia, USA, UK | 14.5 PSI |
| kPa | Kilopascals | NZ door placards, Japanese vehicles, metric countries | 100 kPa |
| bar | Bar (atmospheric) | European vehicles, EU tyre labels | 1.0 bar |
Quick conversion for common NZ pressures:
- 32 PSI = 220 kPa = 2.2 bar
- 36 PSI = 248 kPa = 2.5 bar
- 40 PSI = 276 kPa = 2.8 bar
- 44 PSI = 303 kPa = 3.0 bar
- 50 PSI = 345 kPa = 3.4 bar (common for LT/C-rated tyres)
Which should I use? Use whichever unit your pressure gauge reads. Most NZ service stations and gauges use PSI or kPa. If your door placard uses kPa (common on Japanese imports), divide by 6.895 to get PSI.
🔧 Pressure Calculator — converts between all units automatically
The max pressure on my tyre sidewall says "51 PSI" — is that what I should inflate to?
This is one of the most common and most dangerous misunderstandings about tyres. Here's the difference:
- Tyre sidewall pressure (e.g., "Max 51 PSI") = the maximum pressure the tyre can physically handle before risking failure. This is a safety limit, not a target.
- Door placard pressure (e.g., "32 PSI front, 30 PSI rear") = the pressure your vehicle manufacturer recommends for your specific vehicle's weight, handling, and comfort. This is what you should use.
What happens if you inflate to max sidewall pressure:
- Centre of tread wears faster (ballooning effect)
- Harsh, bouncy ride — less comfort
- Reduced grip — smaller contact patch with road
- Increased risk of impact damage (less cushioning)
The only exception: XL/Reinforced tyres may need higher pressure (36-42 PSI) to achieve their rated load capacity — but this will be stated on your vehicle's door placard if XL tyres are specified.
🔧 PSI Calculator — get personalised pressure recommendations for your vehicle
What pressure should I run XL tyres at?
This is a commonly misunderstood point. XL tyres only achieve their higher load rating at higher inflation pressure than standard tyres.
If your vehicle originally came with XL tyres: Follow the door placard — it already accounts for XL pressure requirements.
If you're upgrading from standard to XL: You may need to increase pressure by 2-4 PSI above the placard recommendation to match the XL's load curve. Use our PSI Calculator for guidance, or get a quote and we'll include the recommended pressure for your setup.
What tyre pressures should I run when carrying heavy loads?
Increase all tyre pressures by 2–6 PSI when carrying heavy loads. Most vehicle door placards show two settings: "normal" and "full load."
General rule: For every 100 kg added above standard occupancy, increase pressure by approximately 2 PSI on the loaded axle, up to the tyre's maximum sidewall pressure.
Common heavy-load NZ scenarios:
• Ute with loaded tray: Rear +4–8 PSI depending on weight. A Hilux with 500 kg in the tray needs significantly more rear pressure.
• Family road trip (5 adults + luggage): All tyres +2–4 PSI above normal
• Moving house: Heavily loaded — use the "full load" placard setting
• LT tyres on commercial vehicles: Follow the load/inflation table specific to your tyre's ply rating. LT tyres can run up to 65–80 PSI at maximum load.
After unloading: Return to standard pressures. Running heavy-load pressures on an empty vehicle causes centre-strip wear and a harsh ride.
🎯 PSI Calculator — accounts for load adjustments
What tyre pressures should I run when towing a trailer?
Increase rear tyre pressure by 4–8 PSI above your vehicle's standard recommendation when towing. The exact increase depends on tongue weight and gross trailer mass.
| Towing Scenario | Rear Increase | Front |
|---|---|---|
| Light trailer (jet ski, small boat) | +4 PSI | Standard |
| Medium trailer (large boat, stock) | +6 PSI | +2 PSI |
| Heavy trailer (caravan, horse float) | +8 PSI | +2–4 PSI |
Why: Tongue weight transfers 10–15% of trailer weight onto your rear axle. Under-inflated rears under towing load causes excessive sidewall flex, heat buildup, and in severe cases, blowout risk.
Never exceed the maximum pressure stamped on the tyre sidewall. Check your vehicle's door placard — many list separate pressures for "loaded" or "towing" conditions.
🎯 PSI Calculator — find your ideal pressure | 🔧 Towing Load Calculator
Can different tyre pressures front and rear upset AWD systems?
Many vehicles specify different front and rear pressures on the door placard (e.g., 32 PSI front, 30 PSI rear). This is fine — the AWD system compensates easily for the minor rolling circumference change from pressure differences.
What DOES cause problems:
- One tyre significantly under-inflated: A slow puncture causing one tyre to run at 15 PSI while others are at 32 PSI changes circumference enough to stress the system
- Left-to-right imbalance on same axle: One tyre at 32 PSI and the other at 22 PSI creates handling problems and confuses traction control
Key rule: Both tyres on each axle should always be the same pressure. Front-to-rear can differ per manufacturer spec.
🔧 PSI Calculator — get correct pressures for your vehicle and load
What tyre pressures should I run on gravel roads?
Drop pressure by 4–6 PSI below your highway setting for sustained gravel driving. This isn't just about comfort — it protects against punctures and chipping.
Why lower pressure helps on gravel:
• Larger contact patch — spreads load over more stones, reducing the force per stone trying to puncture your tread
• Better absorption — softer tyre absorbs corrugation impacts instead of bouncing
• Reduced stone chipping — less impact force means fewer chips gouged from the tread
• More traction — tyre moulds around loose surfaces rather than sitting on top
Typical gravel settings (passenger/SUV):
• Highway: 32–36 PSI → Gravel: 28–30 PSI
• LT tyres: Highway 50–60 PSI → Gravel: 40–45 PSI
Re-inflate before returning to sealed roads. Running gravel pressures at highway speed causes excessive heat buildup and accelerated wear.
📖 4WD Tyre Guide — terrain-specific pressure advice
What pressures should I run for beach driving?
Around 18–22 PSI on firm sand and 15–18 PSI on soft sand for a typical 4WD — and lower for a lighter vehicle. Pressure matters far more here than tyre type or which 4WD mode you are in.
Because it scales with the weight of the vehicle, the useful version of this answer is a table by vehicle rather than one number. A small hatchback wants 15–18 PSI where a loaded Ranger wants 20–25 PSI for the same sand. Our beach driving guide has the full range by vehicle class, along with permits, tides and the beaches you are allowed to drive on.
The rules that matter more than the exact number:
- Air down in the car park, before you are on the sand.
- Keep to 35–40 km/h. Low pressure plus speed is how a tyre rolls off a rim.
- Below about 12 PSI you are risking debeading on standard rims — that is recovery territory, not a cruising pressure.
- Re-inflate before you rejoin the seal, every time. Carry a compressor.
Can under-inflation cause a blowout?
Yes — under-inflation is the #1 cause of tyre blowouts on NZ motorways.
The failure mechanism:
1. Low pressure → excessive sidewall flexing with each revolution
2. Flexing generates internal heat (the sidewall is being bent back and forth hundreds of times per km)
3. Heat weakens the bond between rubber layers and steel belts
4. Internal structure delaminates — the layers separate
5. Weakened area can no longer contain air pressure → sudden catastrophic failure
How fast does it happen? A tyre at 20 PSI (vs recommended 32 PSI) driven at 100 km/h on a hot NZ summer day can reach internal temperatures of 120°C+ within 30 minutes. The rubber-to-steel bond begins failing at ~110°C.
Warning signs before blowout:
• Both-edge shoulder wear pattern
• Sidewall cracking or bulging
• Vehicle feels "spongy" or wanders at highway speed
• TPMS warning light (if equipped)
Check pressures monthly. It takes 60 seconds and could save your life. 🎯 PSI Calculator
Can over-inflation reduce grip in the wet?
Yes — over-inflation measurably reduces wet grip. Here's the physics:
An over-inflated tyre crowns outward, reducing the contact patch area by 10–20%. Less rubber on the road means:
• Fewer sipes and grooves in contact to channel water away
• Higher contact pressure per square cm — sounds good but actually causes the tyre to ride on top of the water film rather than cutting through it
• Less mechanical grip from reduced surface area
How much difference? Testing shows that 10 PSI over-inflation can increase wet braking distance by 5–10% — roughly 1–3 metres at 80 km/h. On NZ's frequent wet chipseal roads, where grip is already marginal, this matters.
The other risk: Over-inflated tyres are more susceptible to impact damage. The rigid sidewall can't flex to absorb pothole hits, leading to bruising, belt separation, and sudden air loss.
🛑 Braking Distance Calculator — see how grip rating affects stopping
How does tyre pressure affect rolling resistance and fuel economy?
Under-inflation is the single biggest controllable factor in tyre rolling resistance.
The physics: Lower pressure means the sidewall and tread deform more with each rotation. More deformation = more energy converted to heat = more fuel burned. The relationship is roughly linear:
| Under-Inflation | Rolling Resistance Increase | Fuel Impact | Annual Cost (NZ) |
|---|---|---|---|
| Correct pressure | Baseline | Baseline | Baseline |
| -4 PSI (~0.3 bar) | +6–8% | +1–2% | ~+$50–80 |
| -8 PSI (~0.55 bar) | +15–20% | +3–4% | ~+$120–160 |
| -12 PSI (~0.8 bar) | +25–35% | +5–8% | ~+$200–300 |
Over-inflation isn't the answer either: While it reduces rolling resistance, over-inflation reduces the contact patch, concentrates wear in the centre, and decreases wet grip. The manufacturer-recommended pressure on your door placard is the engineered optimum.
Use our PSI Calculator to find the correct pressure for your vehicle, load, and conditions. For pressure checking schedules and safety guidelines, see our Safety & Maintenance tyre care guide.
How often should I check the spare tyre pressure?
Every 3 months — mark it in your calendar or check it every time the seasons change.
Spare tyres lose pressure just like your driving tyres — approximately 1–2 PSI per month through normal permeation. But because nobody checks them, spares are often found at 15–20 PSI when needed, or completely flat.
Correct spare tyre pressure:
• Full-size spare: Same pressure as your driving tyres (check door placard)
• Temporary/space-saver spare: 60 PSI (420 kPa). This higher pressure is essential because the tyre is smaller and must support the same vehicle weight on a smaller contact patch. The required pressure is stamped on the tyre.
NZ WOF note: The spare tyre is NOT inspected during WOF — but that doesn't mean it's safe to ignore. A flat spare when you need it is worse than no spare at all (because you've relied on having one instead of carrying a sealant kit).
What is TPMS and how does it work?
TPMS (Tyre Pressure Monitoring System) warns you when one or more tyres drop below a safe pressure threshold — typically 25% below the recommended pressure. A warning light shaped like a horseshoe with an exclamation mark illuminates on your dashboard.
Two types exist — and they work very differently:
| Feature | Direct TPMS | Indirect TPMS |
|---|---|---|
| How it measures | Physical sensor inside each wheel measures actual pressure and temperature | Uses ABS wheel speed sensors to detect rolling diameter differences |
| Accuracy | ±1–2 PSI — shows actual pressure per wheel on dashboard | Detects relative differences only — warning light, no pressure reading |
| Weakness | Sensors cost $50–150 each, batteries last 5–10 years | Cannot detect all 4 tyres losing pressure equally (e.g., temperature drop) |
| Common on | BMW, Mercedes, Audi, Lexus, US brands | Toyota, Mazda, Subaru, Honda, Suzuki |
Why it matters: Under-inflated tyres increase fuel consumption, reduce grip, cause uneven wear, and are the leading cause of tyre blowouts. TPMS catches pressure loss before it becomes dangerous. Even with TPMS, we recommend manual checks monthly — use our PSI Calculator to find your correct pressures.
Can I keep driving with the TPMS light on?
Stop and check pressures as soon as safely possible. The TPMS warning light means at least one tyre is 25% or more below recommended pressure — a significant safety concern.
What the light means:
• Solid light: Low pressure detected. Check all four tyres (plus spare if monitored) with a gauge. Inflate to placard pressure.
• Flashing light (then solid): System fault — a sensor has failed or lost communication. The system can't monitor pressure until repaired.
Is it OK to drive?
• If pressure is only 3–5 PSI low: Drive carefully to the nearest air source (petrol station). Inflate and the light should clear after a few km of driving.
• If one tyre is significantly low (10+ PSI below recommended): Do not drive at highway speed. Inflate or fit the spare.
• If you can't check: Drive slowly (under 50 km/h) to the nearest safe location to check.
NZ WOF note: TPMS is not a WOF requirement in NZ, but if your vehicle has it fitted, the system should be functional. A permanently illuminated TPMS light won't fail WOF by itself, but the underlying low pressure issue might.
See TPMS certification marks guide for sensor replacement, battery life, and reset procedures.
How do I reset the TPMS light after adjusting tyre pressures?
The reset method depends on your TPMS type:
Indirect TPMS (Toyota, Mazda, Subaru, Honda, Suzuki):
1. Inflate all tyres to the correct pressure (check door jamb placard or our PSI Calculator)
2. Find the TPMS reset button — usually near the steering column, in the glovebox, or within the infotainment settings
3. Press and hold until the TPMS light blinks (3–5 seconds)
4. Drive for 15–30 minutes at 30+ km/h — the system re-learns the baseline
5. The light should turn off once calibration completes
Direct TPMS (BMW, Mercedes, Audi, Lexus, US brands):
1. Inflate all tyres to the correct pressure
2. The system should auto-detect correct pressures and turn off the light within a few minutes of driving
3. If the light persists after 10+ minutes of driving, the sensors may need re-programming (requires a TPMS scan tool at a tyre shop)
4. After a wheel swap (e.g., winter set), new sensor IDs must be registered to the vehicle's ECU
If the light won't go off: Check all four tyres plus the spare (some vehicles monitor the spare). If pressures are correct and the light persists, a sensor battery is likely dead — see a tyre specialist. Contact us for advice specific to your vehicle.
Do I need to replace TPMS sensors when fitting new tyres?
Usually no — but the sensor's service kit should be replaced.
During a tyre change with direct TPMS:
• The sensor itself stays on the wheel — no need to replace unless the battery is dead or the sensor is damaged
• The valve stem seal kit (rubber grommet, valve core, nut, cap) should be replaced every tyre change — these parts degrade and can leak. Cost: $5–15 per sensor
• Sensor re-programming is only needed if installing brand-new sensors or swapping to a different set of wheels with different sensors
When you DO need to replace sensors:
• Dead battery — Sensor batteries are sealed and cannot be replaced; the entire unit is replaced
• Physical damage — Corroded valve stem, cracked housing, or impact damage during dismounting
• Age — Sensors older than 8–10 years are approaching end of battery life
• After sealant use — Liquid tyre sealant can coat and block the sensor's pressure port, requiring replacement
Cost: Replacement sensors run $50–150 each depending on vehicle make. Quality aftermarket cloneable sensors are often half the OEM price. If you're ordering tyres from us, book fitting online and we'll check your TPMS during service.
What is typical TPMS sensor battery life and how do I know when it's failing?
Most direct TPMS sensors use sealed lithium coin cells lasting 5–10 years — but actual life depends on how hard the sensor works.
What affects battery life:
• Transmission frequency — BMW/Mercedes sensors broadcast every 15 seconds (drain faster) vs Toyota/Ford every 60 seconds (last longer)
• Temperature extremes — Batteries lose capacity in both extreme heat and cold. NZ's moderate climate is relatively kind to sensor batteries compared to North America or Europe
• Driving frequency — Daily-driven vehicles cycle the sensor's wake/sleep modes more often than weekend cars
• Sensor generation — Post-2015 sensors typically have more efficient electronics and last longer
Signs of a dying sensor battery:
• TPMS warnings that appear intermittently then disappear on their own
• One wheel consistently showing "no signal" or dashes while others read normally
• A TPMS system fault light (different from the low-pressure warning — often a flashing TPMS symbol)
• Pressure readings that lag or update much slower than other wheels
Replacement: $50–150 per sensor including programming. All four sensors are typically the same age, so if one dies, the others will follow soon — consider replacing all four as a set to avoid repeat visits.
Can TPMS sensors be moved to new wheels?
Yes — direct TPMS sensors can be transferred between wheels in most cases.
The transfer process:
1. Sensor is removed from the old wheel during tyre dismounting (it's clamped to the valve hole inside)
2. Sensor is inspected for corrosion, cracks, and battery status
3. A new valve stem service kit is fitted (grommet, nut, core, cap — always replace these)
4. Sensor is installed in the new wheel and the new tyre is mounted and balanced
Compatibility checks:
• Valve type must match — Some sensors use rubber snap-in valves, others use aluminium bolt-in. The new wheel must accommodate the correct type.
• Sensor clearance — Aftermarket wheels with different internal profiles may not provide enough clearance for the sensor body. The sensor must not contact the tyre bead or inner liner during rotation.
• No re-programming needed — When transferring your own sensors, the vehicle already recognises the sensor IDs. Most modern TPMS systems auto-learn which wheel position each sensor is in.
For rim compatibility and upgrade guidance, see our Rims & Wheels tyre size calculator.
Do TPMS sensors need programming — and what does it cost in NZ?
Only when installing new or replacement sensors — not when transferring existing ones.
Programming IS needed when:
• Installing brand-new OEM replacement sensors (new sensor IDs must be registered to the vehicle's ECU)
• Installing aftermarket "cloneable" sensors (these are first programmed to copy your OEM sensor IDs)
• Adding a second set of wheels with separate sensors (e.g., winter wheel set)
Programming is NOT needed when:
• Transferring your existing sensors to new wheels (IDs already registered)
• Rotating tyres on the same wheels (sensors move with wheels — the car auto-learns positions)
• Indirect TPMS systems (no physical sensors — just dashboard recalibration)
How it works: A TPMS scan tool communicates wirelessly with each sensor to read its ID, then connects to the vehicle's OBD2 port to register those IDs with the TPMS module. The process takes 5–15 minutes.
NZ pricing:
• Programming only: $20–50 (often included free with sensor purchase or tyre fitting)
• Sensor + programming: $70–200 per wheel depending on vehicle make
• BMW and Mercedes may require dealer-level diagnostic tools, adding $20–50 to the cost
Get a quote — we can advise on sensor options for your specific vehicle.
Is tyre pressure checked during WOF?
Inspectors don't routinely check pressure against your door placard. But they DO check uneven wear (caused by wrong pressure), sidewall damage from under-inflation, and overall tyre condition. Incorrect pressure causes accelerated uneven wear — which CAN fail WOF.
🔧 PSI Calculator — get correct pressure for your tyres and load
Is TPMS required for WOF in New Zealand?
TPMS is not a mandatory WOF requirement in New Zealand. However, there's an important nuance:
If your vehicle has TPMS fitted from factory: The TPMS warning light is checked as part of the dashboard warning light inspection during WOF. If the light is illuminated, it is not currently a WOF failure reason on its own, but it may prompt the inspector to check tyre pressures manually — and low pressure itself can contribute to other failure reasons (e.g., abnormal wear patterns).
If your vehicle doesn't have TPMS: No issue whatsoever. There's no requirement to retrofit TPMS to any vehicle in NZ.
If you've removed or disabled TPMS: If the vehicle was originally equipped with TPMS and you've removed the sensors (e.g., switching to aftermarket wheels without sensors), the dashboard warning light will remain on. This isn't currently a WOF failure point but does mean you lose a genuine safety feature.
Our recommendation: Keep your TPMS working if you have it — it's a real safety benefit, not just a dashboard annoyance. And regardless of TPMS, check pressures manually at least monthly. See our Safety & Maintenance tyre care guide for a complete checking schedule.
Do valve stems and TPMS affect WOF?
Valve stems: Must be present, functional, and not leaking. Damaged or leaking valves will fail.
If your car came with TPMS, it doesn't need to be functional for WOF. However, keeping it working is strongly recommended — it's your early warning for pressure loss.
Where do I find the full FAQ for each topic?
Each subject has its own guide, and each guide carries the full set of questions for it:
- Reading a tyre size — every marking on the sidewall, including load and speed
- Tread depth — measuring, uneven wear, when to replace
- WOF — every tyre check an inspector makes
- Beach driving — pressures by vehicle, permits, tides and the legal beaches
- Tyre care — rotation, alignment, storage and repairs
If your question is not in any of them, ask us — we answer them ourselves and add the good ones to these guides.
Worn out down the middle, or on both shoulders?
Either way the tread is gone and no amount of air brings it back. 300+ sizes listed online and 15,000+ tyres in stock at Te Puke — cars, SUVs, 4WDs, vans and light trucks.
(07) 573 9090 · Te Puke, Bay of Plenty · Free North Island delivery
Pressure tools
This page explains the subject. These three do the arithmetic — all free, no login.
- Load-and-inflation tables, load range letters and maximum pressures: ETRTO, the European Tyre and Rim Technical Organisation.
- Peter "Jadatis" — the Dutch tyre pressure researcher whose reading of the ETRTO load-and-inflation formula sits behind both the percentage-of-capacity table and the temperature method on this page. He publishes his calculators free for cars, motorhomes and caravans at titunet.nl and answers questions on camperforum.nl. Our thanks — this page would be a lot vaguer without his work.
- New Zealand requirements: NZTA Vehicle Inspection Requirements Manual, in-service WOF and CoF, section 10-1 tyres and wheels, and NZTA's plain-language tyres and wheels guidance on the Land Transport Rule: Tyres and Wheels 2001.
- Rolling resistance and fuel: ICCT, Opportunities to Improve Tire Energy Efficiency; BTMA on tyres and CO₂; and TyreSafe for UK survey data on pressure and tread.
- First-party: every wear percentage, the 40%/6% light-truck split, the 68% not-visible figure and all eight photographs come from our own workshop programme — 1,550 inspections and 1,149 full tread profiles as at 26 July 2026. Photographs © Taylor Houghton. Method and full analysis in the pressure report.
Page © 2026 Tyre Dispatch NZ · Te Puke, New Zealand. Correct as at 20 August 2026. Standards figures do not change; our own percentages will move as the programme grows.
General guidance based on published standards and our own workshop data — reliable but hand-compiled and not guaranteed error-free. Spot something wrong? Email email@tyredispatch.co.nz and we'll fix it.