BFGoodrich Technical Advisory for LT Tyre Pressures

Vehicle manufacturers of utility vehicles almost always fit standard load passenger type tyres to their new vehicles to achieve higher levels of comfort and reduced fuel consumption – If the tyres are upgraded or resized to LT type specification there is a safety and legal requirement to establish the correct pressure for the use and load in laden and unladen circumstances.

Many vehicle owners and operators are unaware that LT type tyres do not carry the same load at the same tyre pressure as non-LT tyres. LT tyre construction & engineering is substantially different, and LT type requires significantly higher pressures to work as the manufacturer intended. LT tyres can carry significantly more weight provided that the correct pressures are used. See table below showing example of the correct pressures for the loads indicated on a very common size.

If the tyre pressure is insufficient over a prolonged period additional heat build-up occurs especially in the bead area and wheel flange. Lower sidewall over-flexing will cause casing fatigue and sidewall cracking is likely to develop. This condition can lead to tyre failure.

NZ driving laws require that the tyres must be correctly inflated for the load. If a customer has upgraded their tyres to LT type construction and or have changed the sizes, then the vehicle placard will no longer be valid as it is unlikely to reference the correct pressure, new tyre specification and tyre type. This website has an easy to use tyre pressure calculator for when different size tyres are fitted from the original equipment (OEM) as well as sizing upgrades to higher load range or flotation tyres (LT) – Please see the screen images below https://tiresize.com/pressure-calculator/.

Example Pressure Table

This LT pressure table excerpt clearly shows a very common example of the carrying capacity of OEM tyres Vs LT type tyres.

Toyota Tundra etc. actually come equipped with Passenger rated tires on them. As opposed to an LT265/70R17, it will usually be either a P265/70R17 or just 265/70R16. This is because not only are they lighter weight and provide a softer ride, but their load carrying and towing limiters such as suspension ability, don’t exceed the capability of the comparable Passenger rated tire.

Despite what many might think, Passenger rated tires can actually have higher load carrying capacities at the same pressure as the LT version in the same tire size. The LT tyre will generally have a higher maximum load capacity, but it takes a higher pressure to achieve the same load capacity.

WARNING! Please note that size-for-size, LT-metric tyres require higher air pressures to carry equivalent loads of P-metric tyres and that any failure to adjust air pressure to achieve the vehicle’s load requirements will result in tyre fatigue due to excessive heat build-up. Due to the higher PSI requirements of LT-metric tyres, they may not be suitable for replacing O.E. P-metric tyres because of the ride harshness that results from higher PSI requirements.

Please see below for some examples of tyre resizing and upgrades to LT products as a guide to the correct and safe pressures for loads.

Our express technical recommendation is to ensure all purchasers and users of resized and LT tyres are aware of the critical and legal requirement to run the vehicle with the correct cold tyre pressures for safety. This will deliver the best service life and assist to avoid a negative customer, user or owner experience.