I've recently purchased a set of 225/60 17 Yokohama GO12s for my Exxy and plan on doing some light 4Wd'ing in the Snowy Mountains over Easter. On the road the tyre dealer recommended 38 PSI front and rear but I also want to find out about the recommended pressures for light 4WD trails, e.g. fire trails.
I know for driving on sand they should be around 18 PSI but what about the harder/sharper stuff like rocks, gravel etc.
Depending on the type of gravel and trail driving it would determine the pressures to drop the tyres to. For fine gravel and relatively small hilly conditions around 30 psi would be a starting point, then for coarser gravel and or muddy / slippery areas and steeper slopes a figure around 25 psi would widen the footprint and provide extra traction.
I usually start at a higher pressure and then see how it goes, it's easier to let a bit more out of the tyres if conditions require a lower pressure. If you carry a small compressor it's easy to air up again before you hit the blacktop.
35-38 normal incl gravel/fire trails - I prefer to keep the sidewalls reasonably hard to prevent the tyres from flexing and building up heat etc.
15 & lower for deep sand
& ensure gauge is accurate at both low and high pressures.
Marty looks like you are in the same sort of area as me so I'd imagine you would be visiting many of the same locations. For mountain trails out towards Blue Mountains/Lithgow and up around Watagans I usually run 26-28psi in the dry. You may need to drop further on wet days. For Stockton Beach I run between 13-15psi but have had to drop lower than that on soft days. You might get away with 18psi on some firmer beaches but not on Stockton.
It would be nicer to also include the tyre size and profile to your replies as Marty has 225/60 tyres which may probably be different from yours.
Fair point Kev. Marty my tyres are 225/65/17 Yoko Geolander ATs. I would imagine they behave very similar to your Yoko's.
I'd be interested in the sidewall height differences between the 65 profile and the 60 profile of the 225 tyres.
As you all should know, the lower the sidewall the more susceptable they are to having cuts when pinched against the rim going too fast over large rocks with lowered pressures or not "bagging out" as much on sand and possibly rolling off the rim if turned too fast at extra-low pressures.
It's around an 11mm difference in the sidewall height. As far as pressures on sand go, I used very similar pressure on Stockton with my old T30 and it had only small road tyres. You do need to be careful at lower pressures not to accelerate/stop too quickly or turn too sharp as the tyres will run off the rim if you are not.
I've got the Yoko 225 size ATs.
As they are slightly wider etc for Bitumen/Highway I would still run them at 33 or 32psi front and 30 or 29psi rear as per Nissan Specs.
Reason being the pressure is matched to the cars dynamics and gives the correct contact patch length for optimum grip and performance.
Also the slightly lower pressure retains designed characteristics for the wider tyre (needs less pressure if tyre has greater volume). These pressures are when tyres are cold.
On trails I run at 28 or 26 front and rear when car is loaded up (ie same pressure front and rear because rear of car is usually loaded with gear and rear weight is about same as front weight [of engine/transmission] - lower pressure if trail is rockier or gnarlier!.. This allows the tyres to flex a little and not get punctures from sharp rocks etc. Sidewalls are no problem on these tyres so no need to run at 38 psi for any reason - you'll just get more punctures for no benefit.
In sand I've never needed less than 24psi. The indication is if the tyre is making deep ruts or not. If the tyres are digging ruts then the pressure is too high. As long as the tyres are "floating" over the sand without too much digging then all is good and the transmission isn't being overloaded trying to get the car to "Plough" through dug in ruts.
If you have higher than 33 psi as some suggest you are shortening the length of the contact patch and actually lessening grip especially in the wet.
Last edited by Translucidus, 16/Dec/2012, 11:12 pm
A while ago, I read an interesting rule of thumb to roughly get the right tyre pressure... 25% rule.
On hwy's, i start with 38-40psi.
When conditions start deteriorating, and you're on gravel, drop by 25% to 30psi
When it comes rougher/rockier, another 25% to around 23.
If really wet or beginning of sand, then consider 18 PSI.
If softer sand, then 13 PSI...
From there, you'll need to see what works - might be 1 or 2 PSI up or down.