Caravan Tyre Pressure Calculator: Bitumen, Dirt & Corrugations
Cold tyre pressure on a caravan dictates caravan sway, tread life, and how much punishment your caravan takes. Use the calculator below to set the correct pressure from your weighbridge axle load, then see the exact speed limits to use when airing down off the bitumen.
Where to Find Your Calculator Inputs
If after reading this section you still have some concerns, keep reading as we provide more details.
- Max Tyre Pressure (PSI)
- Source: Stamped directly on the outer tyre sidewall near the bead.
- What to look for: Text reading
MAX PRESS 450 kPa (65 PSI)orMAX INFLATION 80 PSI COLD. Enter the PSI figure.
- Max Tyre Load (Per Tyre in kg)
- Source: The sidewall load rating block (separate from the size string).
- What to look for: Fine print near the rim reading
MAX LOAD 1060 KG (2335 LBS)orMAX LOAD SINGLE 1150 KG. Enter the kilogram figure for an individual tyre. (Note: If your tyre only shows an index like “112Q”, check a standard load index chart—e.g., 112 = 1,120 kg).
- Weight on Tyres / GTM (kg)
- Source: A public weighbridge ticket.
- What to look for: The axle load of the caravan while hitched to the tow vehicle (Gross Trailer Mass). This measures only the weight supported by the caravan’s wheels, ignoring the tow ball weight carried by the vehicle.
What the Calculator Gives You
The main item the calculator provides is the ultimate pressure you should use on sealed roads. This pressure is measured when the tyres are cold. We will go into this more shortly.
The calculator also provides a table of recommended maximum speeds in situations where you reduce tyre pressures due to road conditions. The amount of deflation is dictated by the road conditions. Keep these numbers handy while on the road.
Why Tyre Pressures Matter
Tyre pressure on a caravan is not only a comfort setting. It is a structural decision that affects how the van tracks, how the tyres wear, and how much abuse the chassis takes on dirt.
Sway control
An under-inflated tyre can have too much sidewall flex. The tyre squirms under load instead of holding a firm contact patch, and that squirm shows up as vague, drifting steering that needs only a small disturbance, a road train bow wave or a crosswind gust, to tip into a full sway event. Correct pressure keeps the tyre’s footprint stable and predictable, which is one less variable feeding the pendulum when something does try to knock the van off line. We cover the rest of the sway picture, including weight distribution and driving technique, in our caravan sway guide.
Even tread wear
An over-inflated caravan tyre causes the centre of the tread to balloon outward. In this case the middle of the tyre does almost all the work while the shoulders barely touch the road. That centre strip wears bald early, and because the tyre is riding on a narrower effective contact patch, braking grip drops with it. Under-inflate it, and the opposite happens: the sidewalls flex excessively, the shoulders carry the load, and the tyre runs hotter than it should. That heat cycling, over and over on a long touring day, is what leads to casing damage and eventually a blowout, often nowhere near a repair shop. It also causes the outer edges to wear more quickly.
Off-road comfort and rig preservation
On corrugations and rough tracks, a correctly aired-down tyre becomes your caravan’s primary suspension component. The tyre absorbs the small, rapid impacts before they ever reach your shock absorbers, chassis, and cabinetry. Using highway pressure on a corrugated road and every one of those impacts transmits straight through the tyre into the rig: rivets work loose, cupboard latches fail, and your suspension takes a beating it shouldn’t have to. Drop the pressure to the right level for the surface, and the tyre does the job it’s meant to do.
How is the Result Calculated
The calculator isn’t a guess dressed up as a tool. It comes from the standard load-inflation principles tyre manufacturers use to rate tyres, scaled linearly to match your actual axle load.
A tyre’s ability to carry weight comes down to two things: the volume of air inside the casing and the pressure that air is held at. Tyre standards bodies (referenced under Australian Design Rule ADR 23) publish load-index tables that map a given tyre’s pressure directly to how much weight it can safely carry. Push more air in, and the tyre can support more weight before the sidewall over-deflects. That relationship is close enough to linear across the working range of a caravan tyre that we can use a simple ratio:
Baseline Cold PSI = (Max Tyre Cold PSI ÷ Max Tyre Load kg) × (Actual GTM ÷ Wheel Count)
In plain terms: take the tyre’s maximum rated pressure and maximum rated load off the sidewall, work out what fraction of that maximum load each tyre is actually carrying on your rig, and apply that same fraction to the pressure. A tyre carrying 70% of its rated maximum load needs roughly 70% of its rated maximum pressure, not 100% and not a number you picked because it sounded reasonable.
How to Input Your Caravan’s Data
Sidewall markings
Every caravan tyre carries two numbers stamped into the rubber that the calculator needs:
- Max Cold Inflation Pressure, usually shown as something like “MAX PRESS 450 kPa (65 PSI)”.
- Max Load, shown as a load index number next to the tyre size (for example, “LT235/75R15 116/113Q”, where 116 corresponds to a load rating in kilograms, decodable from a standard tyre load index table).
Read these cold, before you’ve driven anywhere and before the tyre has picked up any heat.
GTM vs ATM: get this one right
This is the input people get wrong most often, and it throws the whole calculation out.
- ATM (Aggregate Trailer Mass): the total weight of the loaded caravan, including the ball weight, measured with the caravan unhitched and sitting on its own jockey wheel.
- GTM (Gross Trailer Mass): the weight bearing down on the caravan’s own axle(s) and tyres, measured with the caravan hitched to the tow vehicle. This excludes the ball weight, because that portion of the load is carried by the tow vehicle’s rear axle, not the caravan’s tyres.
The calculator needs GTM, not ATM, and not Tow Ball Mass. Tyres only carry the weight that’s actually pressing down on them through the axle. Using ATM overstates the load on the tyres by however much your ball weight is (commonly 200 to 350 kg), and you’ll end up with more pressure than the tyres need. The only way to get an accurate GTM is a public weighbridge, with the rig hitched and loaded exactly as you’d tour with it.
For more on caravan weights you can see Caravan Towing Weights.
Rob’s Tip: We re-weigh whenever we add or remove gear permanently, a second battery, a rear bike rack, anything that shifts the baseline. For the day-to-day swings, a fuller water tank in the morning versus a near-empty one by afternoon, we don’t re-weigh every stop. We just keep our pressures on the slightly conservative side of the calculated figure.
Single vs dual-axle split
The calculator asks how many wheels are carrying the load, because that number divides the total weight between them. A single-axle van with 1,600 kg GTM puts 800 kg on each tyre. A dual-axle van with the same 1,600 kg GTM puts 400 kg on each of four tyres (note that if your caravan is not level, one set of tyres may be carrying more than the others. With a significant difference, this is dangerous). Get the wheel count wrong, and you’ll calculate a pressure for a load each tyre isn’t actually carrying.
Don’t Forget the Tow Vehicle
The calculator determines your caravan’s pressures, but the caravan is only one part of the picture on unsealed roads. Your tow vehicle’s tyres need the same percentage reduction for the same reason: lower pressure on corrugations lets the tyre absorb impact instead of transmitting it straight through the vehicle, protecting your vehicle’s suspension, cabin fittings, and your spine.
Work out your caravan’s percentage drop from the calculator, then apply that same percentage to your tow vehicle’s sealed-road baseline. If you’re dropping the van 25% for gravel, drop the tow vehicle 25% too.
Rob’s Tip: Our sealed-road pressure for the tow vehicle is 40 PSI front and 45 PSI rear. On corrugated gravel, we drop both by the same percentage as the caravan, not to a flat number we picked once and kept using regardless of load or tyre spec. As an example, if we drop the caravan pressures by 20%, we would reduce the front to 32 PSI and the rear to 36 PSI.
Front and rear don’t move by the same PSI amount, because they’re carrying different loads and often run different baseline pressures to begin with. Keep the percentage consistent, not the number.
Why Speed Must Drop When Pressure Drops
This isn’t a conservative buffer added for legal cover. It’s a heat management problem, and ignoring it is how tyres fail on remote roads.
When you drop pressure for corrugations or soft sand, the tyre’s sidewall flexes further with every rotation of the wheel. That flex generates internal friction, and friction generates heat, inside the casing where you can’t see it building. At highway speed, a low-pressure tyre is flexing that much on every single rotation, thousands of times per minute, and the heat has nowhere to dissipate fast enough. The rubber and steel belting inside the casing weaken as they heat, and a tyre that’s been run too hot for too long can separate with no warning.
Dropping your maximum speed alongside your pressure keeps the flex cycle rate down and gives the tyre time to shed heat instead of accumulating it. The calculator’s reduction table works on a simple, practical rule of thumb: match your percentage speed reduction to your percentage pressure reduction. Drop pressure by 10% and drop your maximum speed by roughly 10% as well. It’s not exact physics, but it’s a workable field rule that keeps you on the safe side without needing a thermal camera on the tailgate.
As an aside, most caravan tyre blowouts aren’t caused by faulty manufacturing; they often happen when you run under-inflated. When you see complaints on social media about sudden tyre failures, an unnoticed pressure drop or slow leak is almost always the real culprit. This is why a reliable Tyre Pressure Monitoring System (TPMS) is non-negotiable for remote touring.
On-Road Field Check & Rules
The 4-PSI rule
Check pressures cold, before you’ve driven that day. Once you’re driving, a tyre will pick up pressure as it heats: expect a rise of around 4 PSI for a standard caravan tyre and up to 6 PSI for an LT-rated tyre under load. If you check a tyre after driving and it’s up in that range, that’s normal heat expansion, not a fault. If the rise is well beyond that, or one tyre is running noticeably hotter or higher than the others, stop and check it before it becomes a roadside repair.
Never bleed a hot tyre
Do not release air from a tyre that’s warm from driving to bring it back to your baseline reading. A hot tyre’s pressure is naturally higher than its cold rating, and letting it down to match the cold figure leaves it under-inflated once it cools back down overnight. Always set pressures cold and let the heat rise take care of itself.
Keep TPMS alarms tuned to temperature, not just pressure
If you’re running a tyre pressure monitoring system, make sure the alarm thresholds account for expected heat rise. A TPMS set to alarm at your cold baseline will nag you constantly once you’re rolling. Set the high-pressure alarm above your expected hot pressure, and set the low-pressure alarm to catch a genuine leak, not the normal cold-to-hot swing.
Maintain bead-seat integrity
Airing down has a floor. Go too low and the tyre bead can unseat from the rim, especially when cornering or crossing soft, uneven ground, and you’ll lose all pressure instantly. The situation requiring the lowest pressures is on soft sand. For corrugations and fast gravel, 24 – 28 PSI is the practical floor to prevent rim-strike pinch flats. On soft sand, don’t drop below about 18–20 PSI. In a recovery situation, you may go down as far as 15 – 16 PSI, but be gentle when turning and increase your pressures once you are out.
FAQ
Why can’t I just inflate to the maximum sidewall number?
The sidewall maximum is rated for the tyre’s maximum load, not necessarily your load. If your GTM per tyre is below the tyre’s maximum rated load, running maximum pressure over-inflates the tyre for the weight it’s actually carrying: you’ll get a smaller centre-biased contact patch, reduced grip, and a harsher ride, with no safety benefit. Have the pressure set for your actual weight, not the tyre’s ceiling.
Why does the calculation use GTM instead of ATM?
Because ATM includes ball weight, and ball weight is carried by the tow vehicle’s rear axle through the hitch, not by the caravan’s own tyres. Using ATM would load an extra 200 to 350 kg (or more) into the calculation that the caravan tyres never actually see, pushing your calculated pressure higher than the tyres need.
What’s the lowest safe pressure to run on corrugations?
There’s no single number, it depends on your tyre’s load rating, your actual GTM, and how rough the track is. As a practical guide, most touring rigs on standard highway-terrain caravan tyres sit somewhere in the 30 to 40% reduction range off their sealed-road baseline for typical corrugated gravel, with a corresponding drop in maximum speed. Use the calculator’s reduction table for your specific rig rather than borrowing someone else’s number, and never drop below the point where bead-seat integrity is at risk.
