Part of the preparation for driving off-road is the checking and then deflating or inflating the vehicle’s tyres to alter the tyre footprint to adapt the flotation and grip.
There are few subjects in the world of 4x4s that are under such constant debate. In all six editions of this book, I have revised my opinions because every time I go out and drive, and watch vehicles perform in varying terrain, my own opinions change. At this time, these are my findings:
To take a more scientific look at why reduced tyre pressure have this effect, click here, or read on…
Reducing tyre pressures:
• When traction is marginal such as on steep, undulating climbs or tricky, lumpy descents, shallow slippery mud and general off-road driving, tyre pressures should be reduced by ±20% of normal operating pressures.
• To reduce the shock effect of tyre impact when driving over rocks, pressures should be reduced by ±20%.
• To improve comfort, safety and stability on corrugations, pressures should be dropped by 15%-20%. Be careful of dropping pressures too low when carrying a load because low pressures can also result in reduced directional stability and while making things more comfortable, reduced pressures may also cause handling difficulties.
• Likewise, excessively high pressures, set because of a heavy load or trailer, can also adversely effect handling, especially noticeable on gravel corrugations.
• If conditions require protection, such as on sharp rocks and in conditions where the tyre sidewalls are threatened, then I recommend dropping the pressures by as much as 30%. The trouble is, the lower the pressures the wider the sidewall will bulge, thereby making it more vulnerable. But like a balloon, which is easier to pop when fully inflated than when soft, a hard tyre is more vulnerable to damage by rocks than a soft one.
• If conditions require flotation, tyres should be deflated. On sand tracks where speeds are 40-50 kph drop pressures by 15%.
• On sand that is extremely soft, tyre pressures can be dropped to as low as 0.5-bar. HOWEVER, at this pressure, the risk of a tyre coming off the rim is high. Steer cautiously and drive slowly. Some tyres will not permit such a low pressure as the bead design will not keep the tyre on the rim. In this case, 0.8-bar is about as low one can go. Tubed tyres can be reduced to 0.3-bar safely.
• A vehicle with tubed tyres can be driven more aggressively because the tube serves to hold the tyre on the rim and if the bead is broken, there will be no loss of air. For this reason pressures can be dropped lower than with tubeless tyres.
• At any pressure lower than normal, speeds must be kept down to prevent tyre damage, especially if you are using tubed tyres.
• Excessive speed with reduced pressures, with tubed tyres will quickly wreck the tube and a blowout is likely.
To take a more scientific look at why reduced tyre pressure have this effect, click here.
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