Thread: tyres & pressures for Fraser Is

I'm going to agree with slunnie, based upon my experiences.

I have found 265/75 R16's much better in soft sand and soft muddy conditions than 7.50x16's.

This was way beyond doubt for me. Different times, but similar conditions, with both size tyres on my own vehicle, and at same time with both sizes on different vehicles in the convoy.

The trip I led along the Madigan Line, and some cross country diversions from there, illustrated this vividly. I had 7.50x16's with 12 psi and there was no way I could get up some dunes that others with 265/75 R16's made with some ease. I had to run along swales to find easier places for my vehicle to cross.

Even on my own property, I have bogged all four to the axles when the 7.50x16's break through the crust on the wallum type country. When I changed to the 265/75 R16's I've never had a slightest issue.

Yeah, it's interesting and obviously we'll never get total agreement on these types of issues. More contact area = less pressure = less tendency to sink in the ground. Wider tyre on sand = more sand to push in front but tyre should be less inclined to sink due to larger area. I'm sure driving style also plays an important part in the success of the trip.
cheers Gerald

Originally Posted by Bush65

I'm going to agree with slunnie, based upon my experiences.

I have found 265/75 R16's much better in soft sand and soft muddy conditions than 7.50x16's.

This was way beyond doubt for me. Different times, but similar conditions, with both size tyres on my own vehicle, and at same time with both sizes on different vehicles in the convoy.

The trip I led along the Madigan Line, and some cross country diversions from there, illustrated this vividly. I had 7.50x16's with 12 psi and there was no way I could get up some dunes that others with 265/75 R16's made with some ease. I had to run along swales to find easier places for my vehicle to cross.

Even on my own property, I have bogged all four to the axles when the 7.50x16's break through the crust on the wallum type country. When I changed to the 265/75 R16's I've never had a slightest issue.

Hi John,

The discussion was purely on level to reasonably level beach driving and not really on mud crawling or dune climbing. There appears to be a myth that tyres as wide as 315mm give you better "floatation" on sand and its just not correct...

I'm not an old school stalwart harping on about the benefits or a return to 7.5's at all. In fact I don't even own a set in that size! I do have a set of 235/85/16 A/T's for road and beach use as well as a set of 265/75/16 KM2 for general offroad use and mud tracks.

The discussion was originally on didge's two options (7.5 on 16" and 10.5 on 15") and my point remains that the taller tyre gives the longer footprint and just because the 10.5's (265mm) are wider they are not automatically better for the beach (If the profile/ sidewall height on the 15" wheel is modest, they will in fact be remarkably worse!). It would continue to remain purely on the soft footprint created by the moderately deflated rolling diameter. If the 10.5 (265mm) had the same or bigger rolling diameter I would most probably have gone for them as well...

The 235/85/16 and 265/75/16 has exactly the same rolling diameter, but the 235 remains better on sand IMO and new Defender drivers do not need to spend money to be able to go on a trip in the sand. The 255/85/16 is therefore in my opinion the absolute best sand tyre based on the significant rolling diameter.

I agree 100% with you on the crusty type stuff (Wallum Country you called it?) which sound like "black cotton soil" encountered on the Central African flood plains. Floatation definitely has its benefits if you've got to prevent a punch through on a crust! I always ran 265/75/16 muddies in that terrain and we even managed those to "punch through" on occasion.

Everyone obviously entitled to his own opinion, but I'm not fond of anything other than 16" wheels on a 110/90 or Defender...

Cheers,

Lou

I understood what the OP was about, but the discussion moved a little off topic.

I fully agree with on larger vs smaller diameter tyres and the effect on contact length. And I don't for one second deny the benefit of a long contact patch, vs a short, wide one, and how this transfers to the concept of the hole the tyre is in.

On sand, wide tyres, and coarse tread patterns absorb more power, because of the work they are doing, in moving a greater mass of sand from its original position, out to the side and rear. Without a surplus of power, this is a distinct disadvantage of wide and aggressive tyres.

Perhaps I should read the posts again, but I took it that Slunnie was implying same diameter tyre, when comparing advantages of one tyre size vs another.

Given all other factors are similar, a wider tyre offers better flotation (flotation isn't how I would choose to describe it, but is what was used and many will understand). For a given inflation pressure:

(a) the length of the contact patch will be determined by the diameter of the tyre, and the stiffness of the tyre carcase.

(b) the width of the contact patch will be determined by the tyre cross section, and the stiffness of the tyre carcase.

(c) the indentation of the tyre into the sand will be determined by the resistance of the sand has to the pressure applied over the contact patch (varies for many reasons). The pressure applied is a function of the load over the area of the contact patch. For the same load the larger contact patch will not press so far into the sand (this is where the concept of floatation comes from).

The other comments Slunnie made about 7.50 x 16's are accurate in my view.

I guess dune buggies with wide tyres have been doing it wrong for years
On my next trip to pismo beach ill enlighten them.........
Dc

Originally Posted by modman

I guess dune buggies with wide tyres have been doing it wrong for years
On my next trip to pismo beach ill enlighten them.........
Dc

That's nothing, you wait till I see those stupid buggers from Artic Trucks next - I'm gunna let em have it!

Just because people do things a certain way doesn't necessarily mean its the right way !

Originally Posted by VladTepes

Just because people do things a certain way doesn't necessarily mean its the right way !

My sentiments exactly...

I do however struggle to see how the tyre choice on lightweight 2WD dune buggies and pipe cars relate to a discussion about Defenders on the beach, but everyone to his own I suppose.

Cheers,

Lou