Tyre safety


The basics of tyre inflation

Correctly inflated

Full tread contact patch

Full traction

Optimum braking distance

Optimum handling

Optimum tyre life

Optimum fuel consumption


Small tread contact patch

Less traction 

Longer braking distance 

Poor  handling

Rapid tyre wear (centre)

Worse fuel consumption

Increased suspension wear

Decreased puncture resistance


Small tread contact patch

Less traction (on road)

Longer braking distance

Poor  handling

Rapid tyre wear (edges)

Worse fuel consumption



Vehicle / trailer laden weight

too high for tyre or incorrect

tyres fitted. 

What constitutes 'under-inflation'?

What constitutes 'under-inflation'?

The tyre industry generally refers to tyre pressures in relation to the cold inflation pressure (CIP) that tyre and vehicle manufacturers recommend for particular tyre types, vehicle types and vehicle loadings. The CIP is generally specified on a plate or label on the vehicle.


Pressure 10% below CIP is considered 'significant'.

20% below is considered 'dangerous' and 40% below is considered 'very dangerous'. In EU, original equipment TPMS systems (as legally required for new cars) are set to trigger an alarm at 20% under-inflation. In the US, TPMS systems are set to trigger at 25%

What is a 'blow-out'?

Blow-outs are typically a result of running a tyre when under-inflated – which in turn causes over-heating and progressive reduction of the tyre's integrity. Blow-outs can be caused by tyre defects. And they can be the result of over-loading a tyre – I cover this topic below. 


Blow-outs are bad enough when you are driving a car. When blow-outs  occur with a caravan or trailer, they can be the cause of the tow vehicle over-turning and, terrifyingly, are more likely to cause loss of life.


With caravans, in particular, fragments flying off from a shredded tyre and then hitting bodywork can cost thousands of pounds in repairs. With boat and horse trailers: well . . . enough said.

With WiCaps you have the peace of mind

that what you are towing has tyres at the correct pressure – or warning that you have a tyre issue.

One of these tyres is seriously under-inflated – which one?

What happens if tyres are over-loaded?

Recreational vehicles, caravans, horse-boxes and trailers are all subject to greatly varying loads.

Tyre pressures and tyre types have to be correct for the maximum load (laden weight) being carried.

When a tyre is loaded, its pressure does not increase. However, it does deform and the manufacturer will recommend an increased tyre pressure to compensate for this. If this compensating increase in pressure is not performed, the tyre will overheat (because it is effectively now under-inflated).


Temperature increase causes gas to expand: hence tyre pressure increases* when a tyre is operated (because of heat-generating factors such as friction, tyre flexing, road surface temperature etc). It is normally only a small increase in temperature and an even smaller increase in pressure.

* pressure increases, typically, 0.1 to 0.15° psi per °C, dependent on whether inflation gas is air, nitrogen, whether there is water moisture present and altitude.


When over-loading occurs, there is a significant increase in temperature, particularly in the sidewall of the tyre – which in turn causes pressure to rise. This can also happen with a correctly inflated tyre (under high load) that is not rated for that load. WiCap is very helpful in this situation. If it detects a significant increase in pressure (say 10 psi on a caravan tyre), a major and potentially destructive increase in temperature has occurred. WiCap alerts the driver with a voice message.


WiCaps measure pressure very accurately.

WiCaps, or any other external or internal valve-mounted sensor cannot measure sidewall temperature accurately.

Bottom line: take your vehicle, caravan etc, fully-laden, to a weighbridge. Then, based on the accurate weight you'll obtain, get the tyre manufacturer's advice as to the correct tyre pressures and tyre type that you need.   


I'll be adding more guidance on this page but what follows are links to some very useful sources of advice (including specialist information for caravans, motorhomes and horse trailers).  

What the AA advises:


"Drivers must ensure tyres are correctly inflated 

before travelling, in a bid to reduce the risk of crashing, Head of AA Rescue Noel Keogh has warned".

“You also increase the likelihood of sustaining a puncture which means even more expense."

What the  NHTSA* study reported: 

"that vehicles driving on tires underinflated by more than 25% are three times more likely to be involved in a crash related to tire problems than vehicles with proper inflation."



General guidance on tyres:


What Michelin says:


"When was the last time you checked the pressure of your tyres? Not sure? 
You’ve just answered why so many people drive with dangerously under-inflated tyres. Checking your tyre pressure is inexpensive and simple. Yet why do so many of us fail to weigh up the costs of ignoring this vital procedure? 
"Driving with incorrect tyre pressures can affect a vehicle’s handling, and can seriously compromise safety — leading to incidents that can put lives at risk." 

Find tyre pressures for your vehicle by entering

your vehicle registration:



Caravans tyre advice:




Horse trailers: tyre pressure chart:


Horsebox tyre safety:


Trailer and towing safety guidance:


Stay safe