Any value in switching tyres for our trip?

"An advantage with the BFG muddies is their performance in sand and mud when aired right down they have a softer sidewall which allows them to bag out well at lower pressures than one would expect"

Hi

No advantage in width ("bag out") for sand - its the length of the footprint that counts. Width, by itself, provides no advantage for drive tyres on sand.

A common misconception discussed many times on the forum. A large diameter, bald, skinny tyre would perform as good on sand as a wide, brand new, deflated "muddy"..in fact standard road tyres are fine, just let air out (to increase footprint length).

Possibly some advantage in getting "muddies" for some applications. Think most people get them for looks but I could be wrong :)

Cheers
Greg

Cheers,
Peter
OKA196 Motorhome

might want to reassess your terms the explorer. Tyres don't get any longer unless their sidewalls bag. On balance just because they bag doesn't necessarily mean the footprint gets any wider. Photos above show it perfectly.

Never passed comment on how tyres do or don't "bag" when deflated. My point was that the apparent increase in width created by "bagging" (as suggested by a previous poster) provides no advantage to driven tyres on sand, its the length of the tyre footprint that counts, as perfectly illustrated by the photos (and yes, in this case the "bagged" out part of the tyre isn't even touching the ground i.e. there has been little increase to on ground width anyway).

Cheers
Greg

Agree with Greg, wider tyres give you a bigger "bow wave" of sand in front of your tyre which adds to the resistance, length of tread is where you get the most traction.

Whilst deflated standard road tyres work fine on sand I suspect that side wall failure would be a lot higher with their lighter duty construction.

Oh and how good does a nice set of muddies look :) isn't that the most important consideration in the whole debate! LOL

Hi

My reference to "standard road tyres" was to indicate that, on sand, wide, aggressive tyres are unnecessary. However, as you indicate, there are indeed other factors that need to be considered. In some cases muddies may well be the best choice for one persons intended application.

Cheers
Greg

I only speak from personal experience on this forum, and I have to comment further on this "misconception" which seems to relate more to older tyre choices and individuals own opinions or limited experiences in correctly optimising the use and choice of tyres in sand.

I should mention I was always an adventurous soul and learned to drive on sand and mud in 2WD vehicles as a kid so I have a bit of experience behind me.

There is no question that the length of the tyre alone - adds substantially to the tracton available - this is why tracks are so effective on earthmoving equipment - but a dozer on narrow tracks will still sink well before the same dozer on wide tracks.
The way I commonly use to explain, to novices, the effect of deflated tyres when looking for extra traction is to view them as being 4 mini Caterpillar tracks on your vehicle. This makes sense to them when visualising how the tyre should look for soft sand.
The "bag out" I refer to actually includes tyre length and width ...and yes, with the extra surface area, "width" does assist greatly in sand despite opinions to the contrary.


The "bag" depends on a lot of things but I was referring to a 33' BFG MT which as I stated has soft walls and "bags" well when needed. The Photos above are quite correct but are not the type of tyre we are discussing on this post.
The aired down length available is directly proportional to the available height or diameter of the tyre and the overall volume of the tyre determines how low a pressure the tyre can be reduced to before the weight of the vehicle is no longer effectivey supported by the tyre. IE A low profile small diameter tyre needs to maintain a higher pressure to keep its shape for a given weight than a high profile larger diameter tyre. simple physics as 10 PSI over 10 sq in will carry more weight than 10 psi over 5 sq In.
In essence a 33" Muddie has 1/ height - for a longer deeper footprint, 2/ Width - extra volume (allowing even lower "let down" pressures) and of course extra cm2 for extra traction. 3/ Pliability to allow the side wall to hang out a bit wider when the pressure is low and take pressure of specific points on the bead so the tyre is less prone to popping off the rim.

When driving on soft dry sand (or any surface for that matter), until the tyre sinks into the sand, this bulge is irrelevant. However if climbing a sandy hill or towing another vehicle in soft sand and the vehicle begins to sink into the sand and this bulge sinks below the surface it becomes something like a paddle and provides extra surface area and obviously extra traction. Albeit only marginally extra traction but as the vehicle is still moving this marginal amount of traction AND surface area is often enough to keep the vehicle from sinking further AND in motion. Many aggressive tyres have protective lugs in this bulge area which also help.
From my experience - a similar diameter thinner tyre has little or nothing left - the vehicle stops.

The other issue relates to the driver who controls the throttle. It is also said MT tyres are useless in the sand - this is untrue. They are very effective if they are not forced to dig themselves onto a deep hole by an unskilled driver.
EG
A few years ago at the first cutting on Noosa North shore, I came across a 4X4 Wagon towing a small caravan bogged 1/2 way up the cutting in soft dry sand, below it were two other 4x4s bogged - facing down the cutting - they were both hooked onto the 4X4wagon and caravan and all three 4X4s had become hopelessly bogged. As I had a horse trailer on and was escorting my daughter and friend on a beach ride I had no interest or time to intervene. However, eventually money was offered and the kids encouraged me to assist. So I unhitched the horse float and dropped my tyres till they looked right for the job - so somewhere around 10 PSI. Much to the disbelief of the gathered crowd I pulled in front of the Prado and said "we do this once - we go up the beach not down". (I had better things to do - honestly) I gave them a shovel and tyre guage and insisted on 15 PSI in all tyres and they needed to get the sand away from the front of all their tyres. I had 2 Maxtrax and a front Difflock in my vehicle with 33" BFG MTs. I gave him a handheld 2 way and talked him through the revs we needed to maintain - I.E. when to ease off and when to apply throttle.

Needless to say - It Worked - Once we got moving I actually pulled them all the way to the top without stopping once. At times barely moving but still making progress.

I did know from experience how resilient the MT tyres on my vehicle were to bogging is sand because of all the above factors. Unfortunately we didn't record the recovery on video.

I would like to see how (to quote the Explorer) "A large diameter, bald, skinny tyre would perform as good on sand as a wide, brand new, deflated "muddy""


Consequentially you may forgive me as to why I dispute the "misconception" regarding wide (aggressive) tyres being for "looks" alone.

Maybe I am wrong and any vehicle with 10m psi in their tyres will do this, (if they can go that low and still support the vehicle and stay on the rim) I have recovered quite a few vehicles over the years and personally I have not seen anything else do it yet.


Why do desert racers use wide tyres and not bald skinny ones?

Hi

Firstly we are just talking dry sand here. Different physics involved when other substrates encountered e.g. A bulldozer with "narrow" tracks is not more likely to sink in dry sand - narrow or wide tracks neither will come close to "sinking". Different story in mud and the reasons why something will sink in mud are different to why a 4WD can get bogged in sand (i.e. wheel spin - you dont actually "sink"...but dig yourself a hole).

There are probably several reasons why you would not use bald, skinny tyres in a desert race car, but they are not related to what we are discussing. I was just using it to illustrate that tread pattern and width of a tyre are not the primary characteristics that determine the ability of a normal vehicle to travel over sand without getting bogged.

There may or may not be some benefit in traction on dry sand created by the increase in width caused by reducing a pressure in a tyre (or by using a wider tyre to start with) but point is the lengthening of the footprint is where almost all of the benefit is obtained...the fact that a tyre may also widen a bit (i.e. "bag") plays little part either way.

Fact of the matter is that you dont need "wide" tyres for sand (what is a wide tyre and what is a narrow tyre anyway?) - end of story..but you are free to use "wide" tyres if you wish - there maybe other characteristic of the tyre that are of benefit.

Cheers
Greg

I originally said Dunkbots current tyres had an "advantage" at lower pressures than harder walled tyres.

Fact of the matter is - he already has wide tyres.

My balanced reply was not promoting MTs or espousing superior sand performance.

I do however live and work in a remote area and rely on my vehicle being set up for both mud and dry sand. When the seasons dictate - I like to get home at night. So I put up with my tyre choices for a valid reason.

This forum exists to share information and experiences. ...

Just reminding...

Hi

You seem to have taken this discussion somewhat personally and gone off track (no pun intended) - not my intent. Was just pointing out that the benefit of decreasing tyre pressures (wide or skinny, any brand, your car, my car, anyone's car - doesn't matter who they area, how much experience they have had or where they choose to live) is directly related to a lengthening of the tyre's contact foot print. Some comments provided were suggesting otherwise.

It wasn't about any particular type of tyre or anyone's own particular choice for their specific circumstances, including yours or the OP's.

Yes, the value of the forum is indeed related to the combined knowledge/experiences of everyone, though keep in mind not everything you may read is true/factual...just reminding :)

Cheers
Greg

"A long time ago I took a pocket size sedan down the then unsealed and very rough track from Mt Isa to Boulia on 5.20 x 10 street tyres without any problems."

One like this? :)

Cheers,
Peter
OKA196 Motorhome

Now that brings back a few memories. Looks a bit like Evan Green, Jack Murray and co. back in the mid 60s.

I did not have a roof rack but I did have an S badge at each end.

If only the road down from Isa had been that good.

Here is another mob that forgot to read the magazines and did not realise that they needed lifts, lockers, huge muddies with white letters, super you beaut shocks, twin overhead electronic roo repelling bull bars and heaven only knows what else before you can even think about driving in those areas.

https://www.youtube.com/watch?v=BoQYM7TOnLI

Gelignite Jack Murray and Evan Green were my heroes.
The pic above was the Stuart Highway north of Coober Pedy in 1967 on the way home from Darwin on our honeymoon.
We had a roof top tent that went on the pack rack.
No "S" badge, just a 1963 850.

Cheers,
Peter
OKA196 Motorhome

The tyres, by the way, were Pirelli rag radials. They said we were mad using radials on that road.
They performed faultlessly.

Cheers,
Peter
OKA196 Motorhome

Come on 671, that video is bollocks!!!!!!!!!!!!!!!!!!!things were built to last back then, opposed to today's manufacturing.

Peter_n_Margaret posted:
The tyres, by the way, were Pirelli rag radials.

Mine were standard issue Dunlops. I think from memory they were called SP 141 or something like that. They worked well on sandy surfaces and the rock covered dry creek beds did not damage them.

The thought of reducing pressures back then (1967) never occurred to me and I very rarely do it today. I usually need a Big Red sized sand hill before I even think about it.

I just drove to the conditions and worked on the theory if you are going to hit something underneath then do it at half walking speed. Despite having near zero ground clearance, there was no damage under the car except for a polished aftermarket sump guard that had lost its paint from the grass between the wheel tracks.

“No "S" badge, just a 1963 850.”

That was all you needed. You were just following the same route traveled by Austin Sevens and T Fords decades earlier and they got through ok.

Crusier 91 posted:
things were built to last back then, opposed to today's manufacturing.

Please don’t tell me they don’t make them like they used to. I posted that DVD mainly to show where they went in those days on skinny tyres.

As for the cars: I worked on the *&##@^|! things as an apprentice starting in ’61. All day it was valve grinds, diff overhauls, worn king pins, rusted suspension or steering ball joints and uni joints, riveted brake linings that seemed to wear out in record time leaving the rivets to wear groves in the drums and so the list goes on.

On one customers car, I had to change the oil in its multiple plate clutch every time I changed the engine oil.

There was none of that when I left the trade in the mid 1980s and everything seemed to last twice as long.

Those Redex trials certainly exposed a few structural problems with Australia’s own. I have a book listing the reasons each car lost points in the 1955 trial. Half the Holdens failed to finish and between them there were around 60 body and sub frame cracks.

Of course we still get a bit of that today with overloaded 4WDS fitted with heavier aftermarket suspension. There seems to be no shortage of cracked chassis, axle housings and shock mounts along with collapsed wheel bearings and broken wheel studs.

One consolation though is the aftermarket suspension always comes through unscratched.

I have 33's on my cruiser Bf Goodrich km2 muddies towed a 2 tonne van round australia no issues at all, very good in the wet, plenty of grip in any condition, been on the beach, gravel etc no dramas don't listen to ppl telling you to change them, once worn down if you wish to go down a size or different tread pattern do it then! Sit on 90-95 should keep your fuel use down a bit towing!

Hi Athol,

Thanks for your reply. We're not towing anything on our trip so should be right I hope.

Cheers,

Duncbot