Tyre pressures on corrugations and a good compressor

Submitted: Saturday, Oct 01, 2011 at 13:59
ThreadID: 89319 Views:6611 Replies:6 FollowUps:13
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Since I'm still smiling after the trip we've just come back on, I really wanted to share how tyre pressure really impacts the car on corrugations.

We spent nearly 2000km on dirt recently, across the Tanami from Alice to Halls Creek and then from Halls creek across the Duncan/Buntine to near Daly waters.

I bought myself an ARB compressor, the single cylinder unit mounted in the plastic box for the trip. I also scored a good tyre pressure guage, ezy deflator and some other bits in anticipation of having to use it a fair bit on the trip.

The Prado 120 was loaded pretty much to GVM, we had 180L of diesel in the tank, 60L of Jerry Cans on the roof, additional spare tyre on the roof and the car fully packed. I'd also just gotten rid of the original Toyota suspension and installed the Tough Dog setup.

Across the Tanami I ran the tyres (at cold) to 29LB, when they heated up they were at 32LB. We sat on 85km/hr for most of the way and I must say the ride was fantastic. I was totally impressed at how smooth we ran across the corrugations. Same for the Buntine, absolutely soaked up the ruts. One section of the Buntine I got a little lazy as it was late and i wanted to get into Daly Waters and there were heaps of roos out. at 40LB, it almost shook us to death for the 50KM, I had to stop and let the pressure down.

The ARB compressor made it so easy, it was definitely worth the money. I've put a 50AMP Anderson onto the Bull Bar and put the Anderson onto the compressor cable, its so easy to pull up and plug it in without having to pull the Bonnet.

I spoke to a few folks travelling and I was totally surprised at some of the comments about "I've tried tyre pressures and given up".. Like WOW, was totally the opposite.

I've found the sweet spot for my setup and every time I see dirt the wife "sighs"..compressor time :-)

Again to most folks here I'm probably speaking the bloody obvious but I paid attention to a few of the more experienced folks up here in Alice and it sure paid off !

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Reply By: Kimba10 - Saturday, Oct 01, 2011 at 14:33

Saturday, Oct 01, 2011 at 14:33
Ok, now for us young foke whats that in PSI ?? LOL Glad you had a great trip and interesting to see the difference in pressures. We have a 120 as well but petrol but with OME not Tough dog, any indications of what your economy was with the diesel, Litres per 100klms not miles to the gallon please lol..Glad you had a safe trip............................
AnswerID: 466493

Follow Up By: Kimba10 - Saturday, Oct 01, 2011 at 14:35

Saturday, Oct 01, 2011 at 14:35
Sorry also meant to ask what brand of tyes are you running and are they A/T's or mud or standard (which I doubt) ??..........
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Follow Up By: TheMightyMoose - Saturday, Oct 01, 2011 at 15:46

Saturday, Oct 01, 2011 at 15:46
Sandman has already stated PSI!! Me thinks your young mind is confused.
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Follow Up By: Simon (NT) - Sunday, Oct 02, 2011 at 14:32

Sunday, Oct 02, 2011 at 14:32
Kimba, LB is the abbrev. of Pounds, or PSI, Pounds per Square Inch.


(MightyMoose you could've said that instead of the sarcasm, not everyone knows everything mate, and there isn't a single mention of "PSI" in that post, ONLY "LB", which is incorrect terminology - which leads towards misunderstanding and confusion by persons who may not be as well informed)
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Reply By: Polaris - Saturday, Oct 01, 2011 at 18:25

Saturday, Oct 01, 2011 at 18:25
Great to see you had an uneventfull trip Pete.

Looking at your posted pressures (29 cold / 32 hot) it seems that when the 4 psi rise rule applies then your initial cold pressure is still too high. You have only had a 3 psi rise. With your pressures already logged, I would try for 27 PSI cold and hope to see 31 PSI after at least an hours running.

Tyre manufacturers usually look for a small rise in pressure when the tyre is at operating temperature. Pirelli came up with the 4 psi rule for light vehicles many years ago and it works very well.

Tyres work best at optimal temperature - the reason race cars and bikes are allowed a warm up lap in addition to the tyre warmers that most use.

With less than 4 psi rise - the initial cold pressure is too high.

With more than 4 psi rise - the initial cold pressure is too low.

Just a matter of finding what is best for your vehilce / load / speed - all of which will affect the end result.

happy motoring ...
AnswerID: 466504

Follow Up By: Crackles - Saturday, Oct 01, 2011 at 19:31

Saturday, Oct 01, 2011 at 19:31
If you fit a set of tyre pressure monitors to your car Polaris you will see how ridiculous it would be to try to maintain that 4 psi rise. Just driving down the road with the left hand tyres in the sun can see them inflate 2 psi more than the right. Road surface type, ambiant temperature, variations in speed, even rain will effect tyre pressure so how or even why would you bother trying to keep an exact 4 psi difference?
And seeing you are splitting hairs here of just 1 psi I asume you are suggesting we have our tyre gauges calibrated at a NATA lab :-))
Cheers Craig................
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Follow Up By: Polaris - Sunday, Oct 02, 2011 at 09:35

Sunday, Oct 02, 2011 at 09:35
Crackles - agree compleely! Many points in your post are spot on - especially the variation in tyre pressure gauge accuracy. Need to use the same glovebox gauge - even if the calibration is wrong it will give you an accurate base line.

Tyre pressure monitors are on my list to research and fit sometime.

At least the OP Sandman takes the time to monitor and adjust his pressures to suit the environment. Believe it or not but I have met travellers in the Simpson who would not reduce their pressures and were running 45 PSI - because they had no pump of any description and could not re-inflate ! The track damage caused by the axle tramp had to be seen to believe. Then they wonder why they suffer broken leaf springs!
Same goes for those I've seen with destroyed tyres on rocky roads - due to failure to deflate.

I bet all the Euro tourists driving Britz rental 4x4's have a vehicle that has been supplied with no pump or gauge. Like the Germans who perrished near Lake Eyre some years back when they became sand bogged. I'm led to believe that reducing the pressure allowed the vehicle to be driven out.
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Follow Up By: Sandman - Monday, Oct 03, 2011 at 17:49

Monday, Oct 03, 2011 at 17:49

Thanks on the detailed information, I'm going to have a little more of a read about the "art of tyre pressures and the meaning of life" :-) You've made some good points and I like your followup posting about the 45PSI. Too true about folks not taking a good compressor with them, I simply wouldn't leave home without it !!

I'm not that much of a fanboy to bolt it under the bonnet but I will keep it in the rollout drawers, best money I ever spent....to pump up tyres anyway...

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Reply By: Member - Wayne B (NSW) - Sunday, Oct 02, 2011 at 00:04

Sunday, Oct 02, 2011 at 00:04
Yep tyre pressure sure make a difference to the ride. It has been my experience that 28psi cold is the ideal pressure for maximum grip, ride comfort and puncture resistance. Excess weight will require slightly higher pressure but not too much higher.

Also your speed is critical in minimizing the effect of corrugations. Different suspension setups will usually have a different speed at which the shock absorber / spring rate travel in mm per second will be idealy suited to the frequency of the corrugations.

If tyre pressures are too high the vehicle will skip across the road due to lack of grip / traction caused by the tyre loosing contact with the road.

Wayne B
AnswerID: 466532

Follow Up By: Member - Mick_* - Sunday, Oct 02, 2011 at 00:31

Sunday, Oct 02, 2011 at 00:31
Check out this link:

Its from the guy who changes all the tyres at the Oodnadatta Roadhouse. He is happy to sell anyone tyres, but he also gives out this spec sheet to anyone who wants to save money (and tyres).
He recommends 20 psi in front tyres and 26 in rear tyres.
I know it seems low, but I know guys who swear by this.
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Reply By: Member - Joe n Mel n kids (FNQ - Sunday, Oct 02, 2011 at 03:53

Sunday, Oct 02, 2011 at 03:53
ok i have a different question ...... you seem to me to be loaded up with a lot of fuel ????
How did the fuel usage go for the distance covered, i do admit i have not gone the full length of the Tanimi but it seems to be a heap of fuel for the distance of travel...
I have worked up the Tanimi and near Top Springs (Buntine) so i did not think that fuel was that far apart...
For the "compressor" time... i totally agree, let them down and pump em up as and when required as it makes it a TOTALLY diffferent trip, for instance we can be light loaded and let em down to 23 psi for a good ride, with a big load we let em down to 32 back and 25 front ..... we now go by the "bulge" in the side wall, it very simply dictates to us the load and inflation required .....
AnswerID: 466535

Follow Up By: Sandman - Sunday, Oct 02, 2011 at 10:47

Sunday, Oct 02, 2011 at 10:47
Yes I did take a lot of fuel, more than enough for the Tanami but we were heading to Broome via Derby and I didnt want to buy fuel on the way :-) Turns out the fuel at Fitzroy and Halls Creek was cheaper than what I pay in Alice.

I didnt keep a record of the fuel used but we never had any issues :-) I did bump into some folks at Palm Springs jsut outside of Halls creek on the Duncan and they had to miss Wolf Creek because they were low on fuel however there is an Aboriginal Community just where the Canning starts however they didn't do their homework :-) She said "you should have seen my face when we saw Rabbit Flat closed " :-)

With the Prado I really didnt need the Jerry Cans, the beast has more than enough capacity to get across any fuel issues.

Also I'll do a little more research on the pressures but seriously what a difference, I have absolutely NO hesitation to let them down in future. I remember when I first got to Alice 3 years ago and bogged it in the sand and freaking out as I had no recovery gear and no one knew where we were...it was definitely no fun digging out hot sand from under the car with my hands... :-)

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Follow Up By: vk1dx - Sunday, Oct 02, 2011 at 11:24

Sunday, Oct 02, 2011 at 11:24
Just a short note on large fuel loads. We recently went up through Nyngan to Camerons, Birdsville through Mt Isa to the Gulf and back to Canberra. We have a large tank on order and it would have saved us a bundle. Fuel in Nyngan was about $1.50 per litre whereas in Camerons, Innaminka and Birdsville it was all around 200 a litre. Right where we with standard tanks filled up. Taking at least 50 litres at each site.

We did not keep the figures so I am doing a bit of seat of the pants stuff here.

Taking on 50 litres at each of those places would have cost us arouind 50 cents per litre more than we would have had to spend at Nyngan or if we had the long range tank on board. 200 litres at 50 cents per litre would buy a bundle of beers at $50. Hey?

Long range tanks have their place. Maybe not for everyone though.

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Follow Up By: Sandman - Sunday, Oct 02, 2011 at 14:42

Sunday, Oct 02, 2011 at 14:42

The smaller aboriginal communities were around $2.20 a liter in far north WA and NT. Top Springs was $2.20.... I paid $1.89 per liter at 3 ways..

I carried 240L and didnt have to pay too much through the nose but living in the Territory you simply pay ! Usually I tried to empty the jerry Cans as soon as I could to get the weight off the roof though the ARB Alloy rack did not flex at all with the weight.

I was going to take a 4th jerry can but in the fine print of the Prado 120 specs it has a roof capacity of 100KG...When I bought the rack they gave me the carrying capacity of the rack which I think is 150KG and when I chatted to a few dealers up here (after asking what I drove), they said 150KG. I had the rack, say 30KG, 60KG of diesel, spare tyre of 40KG and a swag, I was over but as I said I got the fuel off the roof as quickly as I could. A few recommended putting a Jerry in the back of the car, even though the diesel is not as smelly as unleaded, I dont think I could have handled it...

All in all the Prado did a great job..

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Reply By: Member - John and Val - Sunday, Oct 02, 2011 at 09:01

Sunday, Oct 02, 2011 at 09:01

Tyre pressures are a critical consideration for several reasons, including:

On corrugations letting the tyres smooth out the ride takes a lot of the effort off the shock absorbers, and saves the vehicle and the occupants a lot of discomfort.

Reducing tyre pressure on sand provides a bigger footprint so better traction on loose gravel.

Dropping tyre pressures even further provides the traction and even bigger footprint required for sand driving.

BUT....... You MUST drop your speed at reduced pressures. You MUST be aware that the load rating of your tyres is drastically reduced at reduced pressures. You MUST be aware too that the optimum pressure/speed combination is very dependent on loading, type of tyre and general vehicle dynamics.

I'm not knocking what you have said, and we routinely adjust pressures to suit the conditions ourselves - sand, dirt, gravel, corrugations, bitumen all have different pressure (and consequently speed) requirements, all influenced by loading, type of tyres, suspension, etc. It is very important though to be aware of the constraints, and note that your optimum pressures won't suit everyone's tyres, loading, vehicle, etc

Rob D recently put all this together in a post here and subsequently a blog. Suggest check it out here.


J and V
"Not everything that can be counted counts, and not everything that counts can be counted."
- Albert Einstein

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AnswerID: 466541

Reply By: Simon (NT) - Sunday, Oct 02, 2011 at 14:16

Sunday, Oct 02, 2011 at 14:16
I just thought I'd add this one in..

As an Outback bus driver we drop the pressures on our front tyres on the buses whenever we go on to the dirt.

Now I don't profess to be anything of an expert on dirt roads but I would conservatively estimate that I've driven about 180,000 kms or more this year alone for work, the majority of that being on our lovely corrugated roads - including the Tanami, the Docker River, the Kintore, and the Mulga Park roads, as well as many more...

Our pressures in the bus tyres (and I'll put up a pic of one of the buses to give you an idea of them) are varied by around 30 PSI.. Most of them are varied between 70 PSI (on dirt) to 100 PSI on tarmac. We only drop the front tyre pressures as it's the front which rides rougher due to suspension set-ups etc, and as the back is dual wheels they are probably running lower to start with.

Basically, dropping pressures makes a big difference. It's definitely work experimenting with your tyres, your suspension setup, and your vehicle to get it right.


Good luck and safe travels for anyone coming out to play on our outback roads, and if I can give anyone any advice to do with these outback roads then feel free to contact me, more than happy to help.

In the attached pic you can see one of our Mercedes Truck based buses. These are absolutely brilliant out on the dirt but they do get a bit of an 'elevation problem' whent the front air bags get pumped all the way up on dips in the road, repeated dips make for a very interesting section of the road where the front suspension rises right up, as does the drivers seat, hehe.
I was actually re-inflating the tyres in this pic after coming back from Kintore, taken at the junction of the Kintore and Tanami roads. (oh yeah, the road was pretty much impassible and my bus was the only thing moving on it that day - thankfully the rear diff-lock makes a huge difference on these buses as they are only two wheel drive). This bus has tyres fluctuated between 65 PSI to 110 PSI.

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Follow Up By: Simon (NT) - Sunday, Oct 02, 2011 at 14:26

Sunday, Oct 02, 2011 at 14:26
now if I could 'edit' my post it'd be nicer to have added this in there. I don't get why we can't 'edit' posts, it's the most annoying thing on this site. *sigh*

Anyway, I just wanted to say that if anyone from this site see's my Pathfinder out here feel free to stop me and say Hi! Or if you see one of the Bush Buses then ask if it's me, my name is Simon, and I'm more than happy to stop for a few minutes and chat about stuff...

Also, due to the nature of the company business we always have the most up to date road reports out there, quite often we know more about the road conditions than the police (because we tell them), and often it is based on our information that causes the roads to be CLOSED to all traffic or changed to 4WD ONLY on the signs.

Ok, enough... safe travelling folks. :)
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Follow Up By: Echucan Bob - Tuesday, Oct 04, 2011 at 09:20

Tuesday, Oct 04, 2011 at 09:20
need a co-driver :)

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Follow Up By: Simon (NT) - Wednesday, Oct 05, 2011 at 23:34

Wednesday, Oct 05, 2011 at 23:34
Bob, frequently mate.. ;)
Actually, I think we are hiring at the moment, just do a search for the company on google and you'll find the site, or just add .com.au after the name.

It's a good job generally speaking, but long, long days.

If however you're not after work and just want to come see what it's all about drop me a private message :)
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