Driving in Sand

[Amesz00]

I have never driven in sand and hope I never will as I hate sand. But I am curious about the purpose of airing down. Is it to make the tire wider or to cause the tire to be cupped in the center. Or both I guess. If it is just to be wider, Then you could argue a 15" wide tire doesn't need to air down?????

As stated, no experience. Just curious.

The tyre doesn't get wider, it gets longer. Wide tyres can help but can also be a hindrance as you have to bulldoze a wider rut.

 

[s.e.charles]

The tyre doesn't get wider, it gets longer. Wide tyres can help but can also be a hindrance as you have to bulldoze a wider rut.

not both? I was under the impression "floatation" was an assist from a bulged sidewall to accept & distribute a portion of traction & vehicle weight.

inquiring minds wanna know!

 

[gait]

not both? I was under the impression "floatation" was an assist from a bulged sidewall to accept & distribute a portion of traction & vehicle weight.

inquiring minds wanna know!

its easy to measure the footprint, the area of tyre in contact with ground, at different pressures. Depends on the tyre I guess, but as I lower the pressure i my Toyos there's negligible increase in width in contact with road, and heaps of increase in length. The curve of the tyre lengthways is much larger radius than the curve across the tread and sidewall.

 

[Mundo4x4Casa]

gait, this tells me that you have stiff sidewalls without much, 'lay down' character or rather narrow wheels, or you didn't really let enough air out to give proper sand running floatation. Every one of my 40 sets of off-road tires over the years had a different low pressure floatational patch size footprint. Depending on lot of factors, every one had a different shape floatational footprint. The best sand tires for my 10K truck camper were 33x15.50R16 (375x65R16) super singles on 12 inch wide wheels. Deflated to 20 pounds, these had a floatation footprint of about 17 inches wide by 18 inches long, plenty enough to keep that loaded 6400 pound rear axle afloat.
The 375's mounted vs. the stock spare:

On 12 inch wide wheels: plenty of sidewall to deflate.

 

[gait]

I think you don't have enough info to make assumptions about my tyres and how I operate. And didn't read earlier post.

Simple maths. Draw a circle around the circumference of the tyre. Draw a circle across the tread. The second circle is smaller. It will deform less as the tyre pressure is reduced. The change in footprint when pressure reduced is much greater in one direction than the other.

Confirmed by measurement.

Just a general principle.

 

[grizzlyj]

I took some photos of my then 395 85 R20 XZLs at about 20psi (road pressure being about 60psi) but I have no idea where I put them.
The footprint got a little bit wider but from less than a foot long to more like a yard. Awesome tyres

 

[s.e.charles]

its easy to measure the footprint, the area of tyre in contact with ground, at different pressures. Depends on the tyre I guess, but as I lower the pressure i my Toyos there's negligible increase in width in contact with road, and heaps of increase in length. The curve of the tyre lengthways is much larger radius than the curve across the tread and sidewall.

after pondering the above I think my stumbling block arose from the (mis)conception the width of the tire only would be lending floatation, rather than total footprint regardless of distribution (front to rear OR sideways).

sideways does help a bit, yes?

 

[gait]

yup, every bit of footprint helps ...

and a couple of psi can be the difference between sinking and cruising

 

[Peter_n_Margaret]

My pictures, Michelin numbers. The tyre is a 305/70R19.5 XDE2.


Example....
Arrived here with the 17% pressure reduction.
Let the pressures down to the 53% pressure reduction and simply drove away. Did not even get the shovel out!


I keep wishing for central tyre inflation

Cheers,
Peter
OKA196 motorhome

 

[Bris31]

My pictures, Michelin numbers. The tyre is a 305/70R19.5 XDE2.

View attachment 485450
Example....
Arrived here with the 17% pressure reduction.
Let the pressures down to the 53% pressure reduction and simply drove away. Did not even get the shovel out!

View attachment 485451
I keep wishing for central tyre inflation

Cheers,
Peter
OKA196 motorhome

Thanks very much Peter, your pictures are worth ten thousand words

 

[Peter_n_Margaret]

Bris31, the pic in the sand is on Fraser Island, just up the road from you.
Cheers,
Peter
OKA196 motorhome

 

[gait]

you don't want central tyre inflation Peter ........... it would last about 30 seconds in some of the squeezy places you've sent me to. Nice in the Sahara (I did dream of it) but I think impractical in Aus. Unless you know of a setup that doesn't clip on the outside centre of hub.

 

[Peter_n_Margaret]

Unless it is a fancy internal one.....
https://www.ftl.technology/products...MIj7WN4Ifs3gIVEBOPCh1TjA3TEAAYASAAEgIF8vD_BwE
Cheers,
Peter
OKA196 motorhome

 

[gait]

nice,

then you'd need even bigger diameter axle shafts .... interesting integration with steer and free wheel hubs.

 

[gait]

snap ......