32 Cold All 'round

15psi for the simpson hey . Are those tyres half empty or half full ?

Wow, your trailer pressures on bitumen surprise me willem???? Most people will run 40 psi on bitumen. As u say......it works for you.

I generally run 32 all round on the bitchy too Willem old mate, and air down almost the same as you, hmmm thats a worry I am scared of rolling off the rims at anything under 15, even rolled a front tyre off in the bloody wet Otways at 16 hmmmm.

I was thinking the same the other day. Especially if there is no load in the vehicle; the front tyres have the weight of the engine over them, you would think they need higher pressures than the rear!

Willem
As you may know we run 7.50r16 on splits
I did the 5 psi rule and run 40 psi in the front and 50 psi in the rear (could go higher in the rear as the rise is around 8-9 psi but left it at 50 psi)
weight of the troopy is 3.3 tonne at the moment (all way ready for a trip)

I dropped the rears to 30 psi in the driveway and they seamed flat????

Before the troopy we had a Prado and ran 35-40 all round bitumen and 29-30 psi on dirt and lower if needed.

Troopy I will drop 10 psi F & R for dirt and lower as needed

will be good to hear some answers

Richard

Bitumen 100-110 kph fully loaded = 38psi cold (tyre retailer rec'd 50 psi) - I'm thinking in thgis scenario about heat build up, so keep plenty in there to make sure walls/tread not overheating

Dirt/rocky-ish but fair surface 60 - 80 kph, same load = 28 psi cold

Gibbers

32 psi on bitumen... Maybe it depends on the tyre but mine look flat at 32psi and they're only carrying me fuel and the second battery(approx. 2000kg)... BFG AT 225/75-16's...

Bitumen 100-110 kph, fully loaded (3.5 t) = 38 psi cold (tyre retailer rec'd 50 psi) - I'm thinking in this scenario about heat build up, so I keep plenty in there to make sure walls/tread not overheating.

Until you, Willem, applied the little grey cells to the front /rear inflation bias, I had not considered it. Currently the truck has 34 in the front & 38 in the rear. Watch out, weighbridge, here I come.

Fast dirt - e.g. Oodna Track at 80 - 100kph, same load = 28psi cold

Dirt/rocky-ish but fair surface 60 - 80 kph, same load = 25 psi cold

Gibbers/station tracks e.g. up north - 15 to 40 kph, same load = 20 - 22 psi (now I have changed tyres, not getting sidewall punctures)

Sand, Bugger all load - e.g. at Robe = 18 psi cold - if in trouble, straight down to 14 psi or so; always gets me out. Have seen tyre seals go at 12 psi or so, but it's always been a wrench of the steering wheel that pops a bead off - and always the front in my observations. Luckily I have not had this experience.

And yes, got a good compressor (Twin Blue tongue), as well as an under bonnett mounted dinosaur, aka ARB.

Hope this helps,

Cheers

Yes Willem I have checked the axle weights on my 80 .
front ---- 1490 kgs
rear ---- 1900 kgs
That was loaded for the Geo Centre trip -- that is with 125 litres water and extra 100 litres diesel mid ships between the axles -one spare on the rack towards the rear and one on rear swing away . The Engel was chockers for that trip plus spares & tools .
Ran 22psi front & 26 psi rears cold on dirt 95 km/hr - smartire indicated 26 & 30 hot so the 4 psi rule worked OK . Temps would settle at 48-50 rears & 44 fronts . after a few hrs. at that speed - one of the best nic nacs I've found .

Willem
From my experience your pressures would be on the low side for a laden troopy running 7.50 x 16's on splits but with your tyres your pressures would be ok.
With bitumen pressures I've mostly stuck to the 4psi rule and it has served me well for over 30 years of 4wd touring.
Inflate them to what you think they should be, then after an hours running at your preferred speed check them, if they have increased pressure less then 4psi then you have too much air in them for the speed and load, if they have increased the 4psi odd you are pretty close to the right pressure and if they have increased more than 4psi then you do not have enough air in them for the given load and speed.
It works with all types of tyres and all types of vehicles.
Apparently it was 'invented' by Michelin.

Hi Willem,

I always run 2psi lower in the front (or higher in the back, whichever way you want to look at it) because I get some odd handling characteristics if I don't. I find the front tends to tuck in in an odd way. Difficult to explain but it happens whatever the pressures so I just always keep the difference at that. It could just be because of the independent torsion bar front end on the Pajero.

I tend to run 38 and 36 on the bitumen with the current tyres but used to run 34 & 32 when I had the BFG AT KO's on as they were just too stiff at any higher. I go down below 20 if I need to on sand but can usually get away with about 24. Mud seems to need below 20.

Tim.

Me thinks that tyre wear contributes to people wanting to run higher pressures too. All tyre places I have spoken to tell me that the vehicle manufacturers don't care about wear - just vehicle comfort, so they recommend the lower end so the drive is more comfortable. Me on the other hand find these pressures too low - the OEM tyres on the Jack would squeal around corners at recommended pressures when 30% tread.

As for the lower at the front debate, I think this is just a comfort thing too. I like to run my tyres at 38-40 on bitumen at the rear, but this in the front is pretty bumpy on the highway, so I lower it to 36ish. Works for me. Don't think I do it though because of a perceived idea that the front is lighter. HMMMM, food for thought.6

D-Jack

The ratio of front pressure to back is determined by the way the car steers. If you have oversteer then the front should be lowered compared to the back. If the car understeers then the front needs to be increased relative to the back.

Oversteer is when the rear tends to hang out or break away around bends. Understeer is when the front tends to push forward and tuck under and the car wants to go straight rather than turn.

If you spend a lot of time in twisties your best pressures will be different than if you drive along straight roads. Also, if you drive faster you need higher pressures.

In order for my Troopy to beat the Ferraris and Porsches through Sydney in the morning rush it is important that the pressures in my superb Hankook muddies are spot on. :-)

Cheers Frank.