Tyre sidewall flexibility value?

Thanks Phil,

If you needed to drop an extra 4-5psi then it would seem that some lateral spread is occurring and aiding flotation, despite some earlier suggestions to the contrary.

Delamination due to the flexing of thicker sidewalls seems a logical outcome too.
So there may be benefit in thinner sidewalls. In truth, I have not staked one yet but have got a cut from a rock.

Now that's interesting Peter. I'll look at that option. Thanks.

Thanks Anthony,

I don't understand the "3 or 4 psi factor" allowance. Could you explain further please?

Hi Allan,

I was trying to say that I think tyres with thicker sidewalls such as muddies (stt's and some others) need to run aprox 3-5 psi lower than an all terrain to acheive a similar footprint size due to the stifness in the sidewalls.

In my experience the lower pressures reqired have never caused any problems such as roll offs or blowouts as long as we were sensible about speed and loading.

Last time I talked to Mr Cooper he was telling me about their new ST MAX which has a strengthened sidewall with an all terrain type tread. Sounds like it might be something to look at if you want stronger sidewalls but I do'nt think they would be any more flexible than any others.

We still went with STT's cause of their track record on our trips of having no problems. Mileage from tyres has always been pie in the sky as far as I know. I have never been able to get more than 50000k from a set of 6 and I think Coopers warranty is a joke and not to be taken seriously, but as long as we are not getting flats, roll offs, stakes or blowouts then I am happy to keep using them.

Hi all

I alternate between BFG muddies and Goodyear Wrangler MTR Kevlar Mud Terrains. The Goodyears are tougher in the side wall that BFGs and Coopers.

On a recent trip doing cross country desert travel in mulga country, despite being the lead vehicle I got less punctures than following vehicles. They ran BFGs, M Thompsons, Duellers and Coopers.

I took my Goodyears back to the dealer, because they are covered by puncture warranty. They said repairing sidewalls are illegal (I knew that) and I paid prorata for new ones; no questions asked. I reckon they have ‘prorated’ me about 8 new tyres now over the last 2.5 years.

The only down sound of the Goodyears are they wear quicker than BFGs so I use my BFGs for routine outback trips and keep the Wranglers for extreme off road travel.

cheers

Hi Anthony,

Thanks, I now understand that the derating was for the stiffer STT's.

I drive on sand a lot and need good 'flotation' to support the weight of the fully laden Troopy. The S/T's have been very good in that respect and only once have I had to drop from the usual 18psi to 15 to get over a Simpson dune at the end of a hot day.
The S/t MAXX were of interest to me but I was concerned about the possibility of increased sidewall stiffness going from 2 to 3 ply sidewalls. Mind you, I'm not confidant that they would have any more resistance to stone cuts.

I have got only 55,000k from a set of six also. And there is no Cooper mileage warranty on the ST series tyres because they say "it is regarded as a more dedicated off-road tyre and mostly used in more harsh terrain than the other patterns". Yet they still highlight their "Mileage Warranty" in their advertising.

I just wish that they did not have white lettering to be sniggered at! LOL

Hi Phil, thanks for that. More food for thought.

Hi Alan
You said

I just wish that they did not have white lettering to be sniggered at!

Come on Alan you know the white lettering on the side increases puncture resistance. It scares the stakes away - lol.

cheers

Hi Bucky,

Yes, there is some good info here without "arm-wrestling". Choosing a tyre is not easy!

Are your BFG's All-Terrain or Mud-Terrain?

I run the Cooper S/T's at 18psi on Fraser Island for example and can drive at 80kh on the firm sand yet can negotiate the soft sand even at Indian Head with no trouble. Your 12psi therefore seems very low. Is it necessary because of stiffer sidewalls? Your comment that tyre bulge is "not that bad" suggests that. And if the lower pressure is necessary, then it suggests that sidewall bulge at reduced pressures does play a significant part in the footprint size.

I run the Coopers at around 25psi on corrugated and stony roads at 80kh which provides good handling and comfort. It would seem that the Cooper S/T's are a somewhat softer tyre.

Allan

I run BFG AT's, as I said in my post.

Please do not read too much into my post. It is not meant to be complicated

I have just found that over the years that 12 psi front and 15psi rear works well. Sidewall bulge is secondary, as footprint is the length of the tyre on the grouond. I have written about this in previous posts.

Never had any trouble attacking anything the Canning threw up at me.
Mind you for the first 20 minutes or so she handled like a boat, as those pressures were hot.

I believe that you can go as low as necessary to do the job as easy on your vehicle as possible. Remembering that we were 4.7 tonne out there, and ate the dunes, easily. Mind you still had to think about what I was doing.


Tyres are the lowest cost of anything to do with a 4x4, and the pressures in them determine how fast, safe, the surface you are on, and how easy you are being on your vehicle,
ie.... if you break something it can cost a lot more than a tyre, so I put my faith in top quality tyres and sidewalls, and a bit of commom sence.

Cheers
Bucky

I'm with you Bucky - well said,

"Tyres are the lowest cost of anything to do with a 4x4, and the pressures in them determine how fast, safe, the surface you are on, and how easy you are being on your vehicle,
ie.... if you break something it can cost a lot more than a tyre, so I put my faith in top quality tyres and sidewalls, and a bit of commonsense."

cheers

Yes thanks Bucky, I appreciate your responses.

I also agree that the cost of tyres is not paramount and I certainly am not seeking the cheapest.

The aim of my original post was to try and determine if tyres with stronger, and maybe stiffer, sidewalls have a reduced footprint when pressure is lowered.

There has been earlier discussion here re the footprint increase with lowered pressure and some expression that it only increases the length, not the width, of the footprint. I am not so sure that is correct as my tyres appear to become significantly wider in ground contact which would add to the footprint area. Maybe I need to go out and do some objective testing.

On the other hand, it could be undesirable to have tyres with such soft sidewalls that the sidewall comes into close proximity to the ground when inflation is reduced as it makes them more vulnerable to damage, particularly from sharp stones, and I do have a couple of sidewall cuts from them. Better perhaps to have stiffer sidewalls and even lower inflation pressure to gain the required footprint by elongation alone? The consequence of that is more rotational flexing of stiffer sidewalls producing heat and stress.

As Phil said...."Can't have everything in the one tyre."

The Cooper S/T's have performed reasonably well for me and I am hesitant to move too far away from them. Maybe the S/T MAXX with one extra sidewall ply may be the way to go.

Thanks everyone for your helpful comments.