Tyre Size
The tyre size below is a typical tyre size definition used by a tyre dealer. Every element has a
denoted description to provide specific information about the tyre.
265/65R17 100T
265 = section width (in millimetres)
65 = sidewall aspect ratio (as a percentage)
R = tyre construction (in this case, radial)
17 = rim diameter (in inches)
100 = load rating (in this case, 800kg)
T = speed rating (in this case, 190km/h)
Deflating
Side Wall Stiffness – Tyres with thicker side wall construction need to be deflated more to achieve
the required ‘Tyre Print’ result.
Aspect Ratio – Tyres with lower aspect ratios are limited to the amount of deflation.
Driving Speed – When a tyre is deflated, there is a higher risk of the tyre separating from the rim
wall. The driving speed must be reduced according to the amount deflated.
Trail Surfaces Softness – The softer the terrain, the more the deflation required. This specifically
applies to sand.
Vehicle Weight – The heavier the vehicle, the bigger the ‘Tyre Print’ required. Therefore deflation is
very important
Trailers – Trailer tyres have to be deflated to stop the tyres digging into soft surfaces and reducing
the risk of damage from sharp objects.
Pressures – Considering the above factors, it is hard to come up with a ‘rule of the thumb’. However
start deflating according to the guideline* below. The ideal tyre pressure for the terrain will only be
achieved by deflating and making further adjustments.
Terrain
Gravel Tyre Pressure psi (Bar)
26-32 (1.8-2.2)
Rocks 22-28 (1.5-1.7)
Mud
Sand 22-25 (1.5-1.9)
18 (1.2)
•
Description
If it is not graded gravel, consider lowering the
pressure based on the load and speed.
Need to increase flex, increase traction and reduce
risk of damage.
Need increased traction especially in soft mud.
Need to prevent the tyres from digging in and the
more area of contact is achieved by lower
pressures.
These tyre pressures are only a guideline. Required pressures depend on all the factors listed
above.