Sand hills - Fast or Slow?

millsy

4x4 Earth Contributer
Last weekend had a great trip around the Ngarkat and Big Desert areas with an old friend and his two mates. We tackled the Border Track, much to my initial concern, but it was not too bad. We all got through. But the way we did it was interesting.

There were four cars - my old MQ SWB, with Westlake A/T's ( no lugs, almost like road tyres ), two diesels with large motors and good off road tyres ( late model Pajero and Hillux ute ) and a little Suzuki with a small motor ( 1.3 litre I think ).

A friend in Adelaide who has had a fair bit of experience explained that he managed to crawl slowly up a steep sand hill off the beach down at Robe. He did it by lowering his tyres down to about 9 psi and kept his revs up over 3000 in low range first gear. All his efforts at charging up in higher gears, and higher tyre pressures prior to this had failed.

But a chap who had just done the Border Track the day before told me to forget about looking after the vehicle ( suspension wise . . . ) and just get as much speed up as possible and power up the hills trying to maintain speed.

I was determined to try the slow and steady method first, before succumbing to brute force. But I think the combination of soft sand, smooth tyres, and lack of skill all beat me. ( But I was running 15psi, maybe 9 or 10 psi would have done it?)

My mate had first tried and failed in his Hillux. Then he dropped his pressures to 15 psi, and with some coaching from his brother-in-law about turning his steering wheel left/right continuously, he actually clawed his way slowly to the top. Cheers and congrats from the rest of us! I tried again using the left/right on the steering. But after a couple of more failed attempts it was time to move on and I went up the 'chicken track' - still slowly and using the steering trick.

The other two had already taken the side track up before we got there and were at the top waiting for us more stubborn types to give it a go.

After that first challenge we all just 'gunned' ourselves over the rest of the dunes. But I felt like I was half driving and half flying! The speed, combined with the bumps meant that I was just bouncing my way up in low range second gear. I felt like I was punishing the old girl and risking suspension damage.

Any thoughts on what's best. How do you do it? What about Big Red? Is it a smooth trip up that hill, or is it a bumpy one also? Fast or Slow? Or can both methods be used depending on pressures?

Other than that little quandry, a great place to visit. If you go, try to do the side track between Scorpion springs and Pine Hut Soak camp site. (This being at the top end of the Track, just where it becomes one-way North to South). The scenery here was so lush compared to other parts of the parks. Dense vegetation with large stands of ‘tall’ trees coming right up to the track. Maybe rather than detour off the Track, it would be better to come into the Track from Pine Hut Soak. It is a really nice camping spot compared to some of the others. Apparently great tracks and views also between Big Billy Bore in the Big Desert, to the top of the Border Track, via Thomsons Peaks Lookout and various other camp sites nearby. But I missed that part of the trek as I had to detour up to Pinnaroo for fuel and Farmers Union IC while the others continued their exploring. I met up with them 2/3 hours later at the start of the Border Track.

We only did the first third of the Track, the one-way section, before turning west to come home. This 28km took about three hours, including the half hour trying to conquer the first hill in the fairly soft sand as explained above. The day before we came across the southern parts of the Ngarkat park from Tintinara to Red Bluff camp ground, and then the next morning across the Red Bluff Track and then up the main (dirt) road called the Murrayville-Nhill road. And two days before this I had come down through the western tracks of the Murray/Sunset Country National Park.
 
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cruiserlad

4x4 Earth Contributer
ive always found sand to be a tyre pressure and momentum thing you need to let the pressures down and give it a bit of stick but not so much that you are in danger for yourself or other people around ive never done desert sand dunes but it would have to be the same princible as beach driving i believe if 7you do big red get there as early as possible in tha morning so the bit of moisture you get from dew over night helps but if a hq holden can get up big red with the right tyre pressure a forby shouldnt have to much trouble
 

millsy

4x4 Earth Contributer
Thanks cruiserlad. Interesting to hear about the HQ! I guess you need to lower the pressure as far as you want to go, considering how many more hills there are after the first one. Then if slow and steady does not work, try again at higher speed. I wonder how much damage you could do to your tires if you go down to 10psi. Could be OK for one sandhill, but I reckon you could 'burn out' your sidewalls if you went too far at these pressures. Could be an issue even at 15psi in terms of longevity of your tyres also! But probably no way out - if you want to go over the top put up with it! Lower the pressures and pay for the damage, or go home and miss the trip!
 
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tiny

New Member
in sand i start at 10psi that gives me the ability to go lower and low range is deffinatly the go less luggy tyres are better as they will float not dig i think you would have found less pressure you would have done it easy with the set up you describe
in sand its all about surface area the more you have the easier it is
 

millsy

4x4 Earth Contributer
Thanks tiny. Am surprised to hear that less aggressive tyres would be better! I just assumed the opposite because of what you see in all the advertising for 4x4 equipment. Its not as simple as what you are lead to believe by all the 'buy this, buy that, buy it now' stuff that you see!

Having said that, just about to send off 50 bucks for 10 issues of the popular 4x4 mag. Come in spinner!
 
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tiny

New Member
my old road tyres where better than my current mud tyres in sand as i said its all about staying ontop not digging
 

grit

Member
tiny is right on the money. Tyre manufacturers usually rate their tyres using the ratio of "road & sand" to "dirt & mud" use.

I have noted previously in another thread that you will achieve more with less aggressive tyres. Along with momentum and selecting the correct gear (with a little experience), will make all the difference.

Sounds like a great trip millsy!
 

Chucky

New Member
in sand i start at 10psi that gives me the ability to go lower and low range is deffinatly the go less luggy tyres are better as they will float not dig i think you would have found less pressure you would have done it easy with the set up you describe
in sand its all about surface area the more you have the easier it is

X2

It's all about tyre pressure, the softer the sand the lower the pressure.
Just remember to pump up the pressure back to road pressures before driving at speed.
Also agree with the tyre choice as well, the less agressive tyre on sand the better.

Lowering tyre pressure should be done even if you are driving over the sand easily.
Firstly, you will do it even easier, therefore saving on fuel and not work the 4by as hard.
Secondly you wont chew up the tracks, sand or dunes as much. It annoys me when a beach entrance/exit is chewed to pieces because people refuse to lower tyre pressures. Or it is blocked by people bogged for the same reason.

As for gearing, I stay in as high a gear as possible, this way the torque doesn't seem to dig me down into the sand. Also as soon as you stop moving forward, stop the wheel spin. reverse up in your tracks and try again alittle faster.
One last thing is turn off traction control if you have it, it will just bog you down faster in sand.
 

Stevesub

New Member
I agree with turn off the traction contorl - if you can!!!.

I have also found our Troopy with 750.16 tyres much better on sand than our Rangie with 255/55.18 tyres. The bigger diameter and narrower tread seems to be the difference. We do a lot of soft sand driving and nearly always need to let the Rangie tyres down but only need to let the Troopy tyres down when it is real soft.

I also use as high a gear as possible and do not let the wheels spin in the Troopy (Rangie has traction control so no wheel spinning). Momentum is the answer to most sand problems although we can do a very soft sand track that we do every couple of weeks at 20kph in our Troopy on standard pressures with no wheel spin but have to do at least 30kph in the Rangie with tyres let down.


When we let the Troopy tyres down, it is usually to 15psi. Next we have to find some dunes to see how we go as most of our sand driving has been on the flat.

Stevesub
 

millsy

4x4 Earth Contributer
Thanks for all the ideas fellas. Really got my little brain whirring with questions about how the sand reacts to a slow climbing wheel compared to a fast "momentum" approach.

I am thinking of the image of the desert spider that builds a funnel trap for its prey. The insect falls over the the edge, and the more it tries to climb up the sand hill to get out, the more it slides backwards. Now if it had a larger footprint, and got those six little shoes running faster, would that save his bacon?

Will have a cruize around the Web and try to pin it down. Always nice to know why!
 

millsy

4x4 Earth Contributer
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millsy

4x4 Earth Contributer
And another article where engineers and scientists were studying how to get a Mars robotic 'rover' to conquer sandhills on Mars . . .

http://www.grainflow.com/index_files/Dunes_Bury05Oct2005_rev2.pdf

Some important ideas from the article are those of 'angle of repose' ( I think meaning the steepest angle that the dune sands can hold before collapsing under their own weight and lack of cohesion between the sand grains). Also the idea of sand avalanches, some travelling up the sand slope, and some travelling downwards, and the speeds of these avalanches.

Am wondering if a 4x4 travels faster than the sand upwards avalanch speed then it will be able to keep climbing to the top of the dune. Slower than this and the 'digging in' effect occurs.

And . ."During the 1930’s, physicist Ralph Bagnold conducted extensive
studies of the sand dunes of the Sahara desert, and in the process developed practical methods to solve many of the
transportation problems he encountered. His best method of getting across a large dune with a fully loaded truck
was to 1) get a high-speed-run-at-it, 2) go-straight-up-the-face, and 3) maintain-full-throttle-to-the-top. Using that
technique, along with reduced air pressure in the tires, and carrying special steel channels to assist in getting
‘unstuck,’ he was able to drive to almost any part of the Sahara he wanted."

Finally, a link to more reading . . . "Traction in sand or soft soils is a subject of much research for the off-road vehicle industry. The Journal of Terramechanics is devoted to this subject. "
 
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chopper

New Member
I'll chuck another thought into the mix regarding tyres.

Aggresive tyres can only 'dig you in' if you have stopped moving forwards, then, couple agressive tyres with an aggresive right boot and you will be conducting your own little sand mine.

I have found, on numerous occasions, that aggresive tyres act like paddlewheels and keep pulling you forward, where an AT or HT would just spin uselessly. The key here, of course, is that once you stop moving, no amount of wheelspin will make you move again.

Sand hills are all about torque to weight, I don;t use the word momentum. you want to have the right amount of torque, at the right time, and you always want enough flotation to stay above the sand.

So set the correct tyre pressures, then use the correct torque to climb the hill.


cheers
 
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