Helping D3 bogged in sand

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Originally Posted by bbyer

I know reducing tyre pressure in sand works but why - what actually happens?

Does the tyre get wider so ground pressure is reduced or does the tread just work better or ....

I ask that as it seems to me that soft sand and soft snow might be about the same to a tyre.

I recall I had a duce and a half 6x6 M135 GMC Army truck with the six 11:00 x 20 non directional CC tread tyres on it. On level icy ground it would be stuck unless the tyres were aired down so I know it works, I just do not know why.

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larger contact patch and lower ground pressure. shallow snow and Ice can go either way, higher pressures get you a smaller contact patch so more ground pressure which in some cases is what you need to stop the tyre from breaking loose (this is usually the go on a thin layer of snow over a hard unfrozen surface), other times you need the lower pressure so you have more tread blocks in contact with each edge of the block giving you a "bite" at the ice which gets you going.

Radial ply tyres tend to grow in length
Cross ply tend to do a bit of both

Also on sand the lower pressure lets the tyre deform more so it can "roll" (kind of bend in) up over the lumps bumps etc rather than cutting through

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Originally Posted by isuzurover

https://www.aulro.com/afvb/images/im...14/01/1348.jpg
http://coopertiresaus.files.wordpres...-footprint.jpg

Your situation on icy ground was different though. Airing down probably allowed the tyre lugs to bite in.

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The diagram used by isuzurover helps explain why the usual advice is to lower tyre pressure on sand.

When I did 4WD training in my old Pajero last century :p the instructor explained that the weight of the vehicle on each tyre is 25% (obviously), so, for example, a 2 tonne vehicle exerts 500kg where each tyre's tread touches the road surface. When you deflate the tyre and say end up with twice the area, the weight per sq cm is halved, ie if the tread area was originally 100 sq cms each sq cm of tyre touching the road would have a 5kg weight load (500/100). Double the area and the weight load would be 2.5kgs per sq cm meaning less download force and hence less tendency to sink into a soft surface such as sand.

Please excuse the numbers above. They were used to make the arithmetic easy. :D

Martin

We had the same issue when we did the Canning stock route, 3 x D2s and 1 wouldn't let his tyres down because he was scared they would roll off the rim being M/T. He was the only D2 that needed snatched on the bigger dunes after having several attempts. The other 2 had no problems.

In some really soft stuff in WA once I had my D2 at 9psi to get thru and not doing anything stupid I managed to keep the tyres on

Cheers Ean

I usually start at 25, specially on the beach as some of the wetter sand sections can be pretty firm and you can travel at up to 80kph and I don't like driving on hard surfaces at speed with very low pressures. I haven't been bogged yet, but am always prepared to let them down further if need be.

I have two sets of easy downs purchased for about $20 each on eBay. I have one set at 25psi and the other at 18psi.

BobD - I know there are probably hundreds of threads on tire size, but noted you have 285 60 R18 on your D3. Do they fit the arches without rubbing or any mods? I need new tires all round and want a decent all terrain - prefer not to have to change rims to 17's to get a decent tire in. Thanks

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Originally Posted by Dapper

BobD - I know there are probably hundreds of threads on tire size, but noted you have 285 60 R18 on your D3. Do they fit the arches without rubbing or any mods? I need new tires all round and want a decent all terrain - prefer not to have to change rims to 17's to get a decent tire in. Thanks

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have a look at the spreadsheet Gordon has put up on his web site. It has a large range of tyres from 17's up to 20's and tells you if they fit or not along with pertinent tyre measurements:

Green Oval Experience Land Rover 4WD, Range Rover off-road Australia

When we head into the dunes from Two Rocks (North of Perth) I drop my tyres down to my set '16psi' on the Staunt type valves. I believe thats more like 20-25 and it will get to to most places. Similar situation when I had the Triton.

IF its not going, I lower them further and I've always been able to get out. D3 was on its belly last time with the suspension extended to the max, dropped the tyres and out she went - no issues.

I often wonder why people go out in 265/285 size tyres without letting any air down and then wonder why they struggle up the hills - big size tyre doesn't matter - need some air down regardless.

I was in Bremer Bay over Xmas and went onto a beach called Back Beach and got bogged to the eye balls in very soft fluffy deep sand to the point where it went into extended mode. (not pic below, forgot to take a pic when bogged :wasntme:

Any way got the max trax out and the shovel and got out of it no problem.

The tyres were at 15psi and did not feel confident in letting the 255/55/19's down much more as the beach sloped down in places.

This was the only time I got stuck out of the eight days we were there.

I used the sand setting,DSC off, low range 4 and 5 and it did it easy.

My mate had a Triton diesel, I gave him a drive of the D4 and he couldn't believe how easy it went along the beach. Didn't rev over 2000rpm where the Triton had to be at 4000+ to maintain momentum.

I had the LTZ Coopers on the sport and I can't wait to get them on the D4, then it will be a weapon in the sand.

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Originally Posted by Dapper

BobD - I know there are probably hundreds of threads on tire size, but noted you have 285 60 R18 on your D3. Do they fit the arches without rubbing or any mods? I need new tires all round and want a decent all terrain - prefer not to have to change rims to 17's to get a decent tire in. Thanks

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Dapper, I have a D4 and my tyres rub slightly as mentioned in the GOE information mentioned in the post after yours. I haven't done any mods and the plastic liner has worn through in front of the rear wheels where the seam protrudes slightly as mentioned in the GOE information. No damage to the tyre though. I don't know whether the D3 is different or not.


Bob