Tuesday, Jun 11, 2013 at 18:37
Indeed it is more more than "marginally"!
As you say, in soft sand and sometimes when
rock crawling we can get down to very low
pressures, but the risk of rolling a
tyre off the rim is always present, and (also as you say) speed must be reduced to prevent the
tyre from overheating etc. It also depends on the mass of the vehicle, the size and type of the tyres etc. as to what is required. I found that the cheesecutters on my old Hilux behaved very differently to the much wider tyres on, for example, my wifes Prado, presumably because of the far taller sidewall together with a lighter overall weight (unladen). I also have a suspicion that one of my old SWB "Series" Land Rovers has no
tyre pressure at all, the age-hardened tyres stay up without air!
So my advice, when facing corrugations, is to reduce the pressure marginally - perhaps 10% or so - and see if it makes a difference. Especially the first time, when you don't know how that particular combination of
tyre, vehicle and load will react. Then reduce a bit more if required. On the other hand, when experience tell you it is OK to drop straight to 16psi to travel over sand and the driver knows to slow down, then that's fine too!
The link you posted is indeed interesting, though it doesn't mention the issue of legalities. If the maximum
tyre size on the vehicle was the starting size (stated as 265/75R16, but with mention of 17" alloys at some point), then changing to 285/75R16 wouldn't be legal in NSW without an engineering certificate.....though it would be OK in QLD and VIC......unless a
suspension or body lift had been undertaken at which point it might not be. Don't you just love the rules!!
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