We asked an expert to answer some tyre questions
What importanceis the of taking temperature into account when measuring a tyre’s pressure, especially at the extreme ends of the pressure spectrum?
Compressed air contains water vapour. This has a higher variation to pressure changes due to the expansion in volume when it heats up. For this reason, it’s advisable to check your tyre pressure when the tyre is cold and has not been subjected to the rising ambient effect of the sun or the heat generated by the friction from driving. This is even more critical at the top end of the inflation spectrum – the tyre manufacturer has a max inflation pressure rating on the sidewall of the tyre that must be adhered to.
Why do tyres lose pressure by themselves and how often should you check your vehicle’s tyres?
Tyres lose pressure due to a number of reasons: leaking valve stems, slow punctures, poor fitment, impact breaks and osmosis, which is when the air molecules pass through the inner liner of the tyre over time. It’s possible to lose 1 to 3 PSI per month depending on the type/ quality of the tyre inner-liner compound and thickness. For most types of driving a weekly tyre-pressure check is ideal, but every two weeks is adequate.
Why is it necessary to rotate your tyres? And if you do, how do you rotate them?
The rotation of tyres allows for a more consistent and even wear pattern over all four of your car’s tyres. Front tyres tend to have a higher wear rate on the shoulder (particularly in front-wheeldrive vehicles) Rotation will certainly extend tyre life. Ideally the tyres should be rotated from front to back or vice versa. If the tyre is one directional, ie. it can only rotate in one direction, then it can only be moved forwards or backwards and not to the other side of the same axle.
Any other suggestions to extend your tyre’s life?
An important element in tyre life extension is to ensure that your vehicle’s wheel alignment is correct – this will prevent unnecessary scrubbing of the tyres from toe-in or toe-out. This, together with correct inflation and rotation, will give your tyres the best chance at optimal life span.
How far can drivers safely deviate from recommended pressures, and for how long a period or at what speeds (in km/h) before running into problems? People often do week-long trips in the Namib at pressures of between 0.7 and 1.0 bar. Is this safe?
The recommended pressure is specified to support the maximum load-carrying capacity of the vehicle. A tyre’s pressure should only be deflated for the period of time that it is operating in that environment, i.e. when in sand or mud deflation is appropriate to provide better traction due to a wider footprint. Once the vehicle leaves this terrain and moves onto a harder surface such as graded dirt or tarmac, the tyres must be inflated as soon as possible to avoid damage. As the speed of the vehicle increases, so does heat, and by not inflating the tyre correctly, premature wear or even failure can occur.
If you want to buy tyres for your 4x4 that are more suited for off-roading than the standard HT tyres, what should make the difference when deciding between AllTerrains and Mud-Terrains? When deciding on what tyre to purchase, one must weigh up the pros and cons that are relevant to the application of the tyre. Let’s look at some specific performance criteria. For AT compared to MT: • Tread blocks are more closely spaced and more rubber is in contact with the road surface. • The AT tyre has more sipes which lets the blocks flex with ease for improved grip. • AT tyres will provide better highway/ road performance due to its 50:50 characteristics vs a MT tyre which is typically an 80:20 tyre (80% offroad usage) • The MT has bigger gaps between the tread blocks and a smaller solid to void ratio (solid = rubber and void = gaps) which aids in clawing on loose surfaces and digging in mud. • The construction of the MT, which is typically a 3-ply sidewall, makes for a less compliant/harder ride – this will be more noticeable on the tar when your pressures are higher. Is one spare wheel enough when going on an overland trip? Any suggestions on repair equipment to get by until you reach “civilisation” again? Apart from plugs, what about gaiters? What do you recommend keeping in mind from a safety point of view when having to resort to such emergency repairs? For relatively short overland trips, one spare tyre is usually sufficient when used in combination with a good quality tyre sealant, compressor, and tyre repair kit. However, if the terrain is known to be particularly tortuous and you’re reasonably far from civilisation, then its best to carry an additional spare tyre. Practically, plugs and gaiters are sometimes necessary in emergency situations, but we do not recommend them for extended use, i.e. if the cut is on the shoulder or sidewall, the tyre should be replaced at the earliest possible opportunity. What is the most important characteristic to you: grip or tyre life? And why is it that these two are often mutually exclusive? One needs to understand the application and vehicle type prior to making this decision. Tyres with excellent grip characteristics generally wear quicker due to microscopic particles that get torn off under acceleration/braking/cornering. Conversely, tyres with excellent tread wear characteristics minimise rubber being removed. Bear in mind that operating conditions are also important, in other words does your vehicle spend most of its time driving in hot/dry conditions or wet/cold? These are also important determining factors for which type of tyre would suit you best. If All-Terrainsyour vehicle (not is to fitted mention with Mud-Terrains), how should you change your driving style or what do you need to keep in mind when driving on tar, especially in wet weather? A 4x4 SUV or bakkie fitted with HTtype tyres is the ideal solution for good road-going abilities. Once you’ve changed from HT to AT or MT-pattern tyres, you should be aware that you’re compromising the road ability of your vehicle. To ensure that this compromise is less noticeable, you should do the following: • Increase your following distances – your braking distances will increase in the dry, but even more so in the wet. • Ensure the speed rating is equal or higher than the original tyre and that the tyre is suited to maximum vehicle load. • Lower your speed – your vehicle will not corner as quickly or predictably as with the HT-pattern.