Tyre Pressures and off road vehicles

[AB]

Some of Andrew St.Pierre White's off-road training. This time, the effect of tyre pressures on off-road performance

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[the evil twin]

Greetings all powerful and imperious Admin... You spotted the discussions we were having over in the Auto Tranny thread eh...

First I freely admit that I used to drop my pressures way down when off road and it wasn't until a few years back that I changed on the advice of a Comp driver when I asked him what to run in my newly purchsed Pro Comp Xterrains... his answer blew me away as they were MUCH higher than I thought.

Currently I run Coopers and I use the pressures recommended by the Manuf which incidentally are close to what I used in the Pro Comps

Cooper Tyres pressure recommendations (and indeed I have found them to be pretty good for my Cooper Disocverer's are MINIMUM (go higher for loaded truck)
Gravel - 32 PSI
Rough Gravel - 26 PSI
Rocks - 22 PSI
Mud - 22 PSI
Sand - 18 PSI

My truck is very heavy with the gear I carry and I actually run higher by about 2 to 4 PSI except on the Beach Sand around SWWA which is like Custard so I drop to 16 to 18. Get onto the hard packed southern beaches of the Southern Ocean and you can stay higher

Different people will have different views which is totally cool... I was advised that higher pressures have the advantages of
1 protecting the side walls... in LT tyres the tyre stands upright and puts the tread between the case and sharp objects
2 less chance of spinning the tyre on the rim
3 less chance of crap in the beads
4 less chance of popping a bead
5 less chance of internal tyre failure... the ply's are not "working" against each other as the tyre distorts laterally

BUT... the bottom line is 'The right presure is the one that works for you'. I just used the Manufacturer's recommendations as a starting point and found them to be excellent 'cept for the local sand conditions

[AB]

You spotted the discussions we were having over in the Auto Tranny thread eh... - Yes, you caught me ET.:)


BUT... the bottom line is 'The right presure is the one that works for you'. I just used the Manufacturer's recommendations as a starting point and found them to be excellent 'cept for the local sand conditions - Exactly right, whatever works for you mate, I've also been known to drop mine down ridiculously low and almost ripped off the rims up at Fraser Island and Simpson in certain spots, just depends on what works for you and the situation.

I love the part in this video where the second guy is demonstrating by lowering the PSI to hug the log and get over and he almost didn't make it. it actually worked 10 times better with a higher PSI..haha.

He then mentioned he had no idea why it was happening...They should have cut that bit out I think.

[AB]

He had to be in 2wd for that to happen. Oops! Is this guy a recognised 4x4 guru? He should sack his video editor.

No guru that I know, just a 4wd trainer not associated with this site at all.

[patch697]

G/day ET I agree with your advice. I do a lot off road in the sand also & tend to do most if it at between 18 to 25psi I have gone down to 10psi but only over a very short distance but as you already mentioned it really depends on the circumstances.

Cheers
Paul

[ilikedonuts_10]

Would these change for BFG all terrains? I was talking to a guy who said they didn't have as strong tyre walls so they might be different?

ta

[Finly Owner]

As I have said b4, we did simpson desert in HG Holden and did not go real low on pressures and made it all the way through without tyre damage, and only being towed over two or three dunes.

[Ruby]

To get highway pressure, I use this rule of thumb (used for years not sure where I came across it).
Check pressure cold (car full loaded)
Check pressure after an hour of the driving on the highway. If the PSI is greater than 4 psi the tyre is over inflated, less than 4 psi the tyre is under inflated.
I wouldn't just deflate/inflate (unless they are excessive) to the same amount as the pressure / temp are intrinsically related. I just ensure that I keep it in mind and adjust it the next time the tyres are cold

Cheers

TOOR

[the evil twin]

To get highway pressure, I use this rule of thumb (used for years not sure where I came across it).
Check pressure cold (car full loaded)
Check pressure after an hour of the driving on the highway. If the PSI is greater than 4 psi the tyre is over inflated, less than 4 psi the tyre is under inflated.
I wouldn't just deflate/inflate (unless they are excessive) to the same amount as the pressure / temp are intrinsically related. I just ensure that I keep it in mind and adjust it the next time the tyres are cold

Cheers

TOOR

Other way around isn't it?

If the pressure changes by more than 4 PSI then the tyre was initially under inflated and is generating to much heat and is in risk of a case failure ?

Thats why you have to slow down with tyres aired down... to keep the temps down

[YNOT]

Other way around isn't it?

If the pressure changes by more than 4 PSI then the tyre was initially under inflated and is generating to much heat and is in risk of a case failure ?

Thats why you have to slow down with tyres aired down... to keep the temps down

I think ET is right.

The 4psi rule has been mentioned on here before and although I have never tried it I think it is a good rule of thumb.

Tony

[Ruby]

Hi Evil Twin, well picked up, my mistake, I got it twisted around when I was typing it up. Good to see someone caught it

[Ruby]

I did a little research to see where I originally found the rule and found this review. (http://www.aawen4x4.com.au/index.php?option=com_content&view=article&id=1:4psi-rule&catid=2:current&Itemid=7). Read a little further into it and it looks like they are advocating a 6psi rule for 4wd due to the tire construction. Once again well picked up ET and Tony

[Tim30]

Nice tips thanks guys for your input.

[chollyfunk]

Here in the desert in Qatar we had those big old balloon tyres. Sometimes if the sand was particularly soft we took the pressure right down to 12-14 psi.

[twisty]

... You spotted the discussions we were having over in the Auto Tranny thread eh...

What Auto Tranny thread?

[xiyue077]

thanks evil twin. These data are quite helpful.

[stewart118]

This was helpful

[Blann]

Hi all,

After hearing many a theory from many people who all have their own take I spoke to an army driving instructor. His advice to me was whatever your tyres are at height wise from road to rim take 1/3 off for example my tyres on my gq are at about 150 mm if I bring them to 100 and drive sensibly ill go anywhere. HOWEVER if you do choose to run your pressures at this you may need to change your driving style. At that pressure you run a risk of damaging tyres as aforementioned, so you need to keep it steady and controlled. I've never torn a tyre off and my pressure generally on almost all sand is down at 12 pound and I've seen many people rip tyres to shreds at 16 to20 pounds because they drove too hard or just in an ineffective way.

This is only my advice, so take it all in because there may be a better way out there, but give it a go. Experiment and keep changing and see what works for your truck in each terrain.


Happy drivin

[kegatron]

Thanks to the OP for this one, Cheers. would have liked to see a bit more on sand techniques.