Tyre pressure on rough tracks?

It's difficult to say with absolute certainty (there are a LOT of variables) but it is quite possible that dropping your pressures would have helped, yes.

The reason is that when you reduce pressure, the tyre carcass is able to flex more - this allows the tread face and even the sidewall to sustain an impact without being torn.

Think of your tyre like a balloon. When you have a balloon inflated till it is hard and you press a pin against it - the balloon bursts. When you have a balloon inflated only half way, you can press the pin fairly hard against the balloon before it pops. Very simplified example but the concept is similar.

Hope the info helps.

Anthony

Sigmund,

Yes and no.

Do you have highway tyres on your Forrester?

Yes, reducing your tyre pressure will improve the ride as well as reduce the damage to the tyre provided you have reduced your speed as well.

Side wall damage tends to happen at speed or when hitting rocks, cornering can also cause issues and side wall damage.
Staking a side wall is a fact of life, again lower pressures and reduced speed helps, but only light truck tyres with multiple plies can help here.

Personally no faster than 80 kms.

I drive a Landcruiser.
Tarmac pressure on Cooper STT's 45 psi
(long distant) Dirt/gravel road pressure 30 psi
Sand 20 psi (or lower depending on condition).

High tyre pressure on dirt and gravel tracks can cause fractures in the tyre plies, tyre chipping and side wall damage.

High speed on deflated tyre can cause side wall pinch (between road and wheel rim, tyre rolling off the rim if cornering at speed.

If you go to the Cooper Tires web site, they will send you a free booklet regarding tyre pressures. This is relevant for all tyres.

Thanks guys.

That's v. helpful.

Yeah, they are (were!) highway tyres. For the first I was driving pretty slow; the 2nd at about 50 kph. Had only just bumped the pressure up from 30 psi at the dealer's recommendation and didn't think about how that would play out with rocks.

The only choice of replacement after being trucked out turn out to be optimised for wet weather. Darnit.Well, maybe that'll bring some rain to Vic.

We just went through the Simpson, old Ghan track, Bogey hole etc and came across a variety of opinions re tyre pressures.

One tyre repair guy said 50psi! Other said to let them down, even for rocks. Obviously for sand the only way to get through is to let them down - we went down to 12psi at one stage with no problems.

Personally I think the softer is better than harder and I have a pretty good record in terms of punctures or tyre damage.

Dion
mycampgear.com

Not it wouldn't! Its just luck. Its no different if you were at road pressures driving on bitumen and you had a blow out or a puncture.

Some passenger tyres have incredibly thin walls, especially at the shoulder - you can feel how thin, on a tyre that is off the rim - just give the shoulder a 'poke' - seems to me manufacturers use this factor (among others) to provide a silky smooth ride in cars that they suggest can "conquer any terrain".
Light truck tyres are much tougher overall, but transmit more vibration as as result. As for flats .... if you were to fit robust tyres, get a compressor (so that you can adjust pressures to suit terrain) and take it easy most of the time, you might easily wear out a set with no issues at all.

I run road pressures when out in the bush of 40psi. When I hit the dirt I employ a 25% rule.

When i get onto good dirt roads like say the Strzlecki or Birdsville Tracks I drop the pressure by 25% so they come down to 30psi

When the track deteriorates I drop again by 25%. so now they come down to about 22 or 23 psi. The next step is usaully the sand so down 25% again and that puts me at about 16 to 18 psi. If I get stuck, you guessed it I drop 25%, at about 12 psi I have never been stuck or had a puncture. Just remember that as you lower your tyre pressure you lower your speed.

These are starting points but I find that this rule gets me through most problems. Current tyres have 70k on them with only one puncture. I really should sweep the garage floor after doing some woodwork.

Duncs

Depending on the weight of the CT you could probably drop them more.
EG axle load of 2.8 tonne LC minimum 700KG and probably 900 at the back.
Axle load of 1tonne CT say 450Kg .

So each car tyre has 450Kg and each CT tyre 225Kg.

Its pretty obvious that the CT tyre needs to be much lower to have the same footprint as the car assuming same type tyres.

Regards Philip A.

Hi Sigmund,

I have a friend with a Forester who after puncturing 5 tyres on Tassie bush tracks opted for light truck tyres. Hasn't had a problem since. His explanation as discussed by others was that the standard tyres supplied on the Forester are thin walled. He to my knowledge has never dropped tyre pressure, neither have I. If you dropped tyre pressure every time you went on a dirt road over here getting from A to B would be tedious. Have H/T tyres on the Suzuki and no punctures so far but I suppose we don't travel the same distances on corrugations that you do on the mainland. Have travelled ~100kms at a time on corrugations without problems but have done that in a sedan as well.

Thommo

On the left hand column on this site, under "search by topic" click on : 4WDriving
then click on:
4WD Skills and Rules
that article will give you some idea about tyres, pressures and driving skills. Hope this helps.

check this site out for an explanation of what happens with different tyre pressures.
tyre pressures

Thanks again all for the good oil.

Lots of good info.

What struck me on a plain gravel road with 34 psi was how poor the traction was compared to 30. With the lower setting power slides were no drama; with the higher setting, it felt slippery and I didn't try to power slide.Well that's just an aside, and I wasn't fooling around on this trip.

The std tyres are Geolanders and the Forester community is pretty sour on them; I wouldn't know since this is my first 4by (kinda).

Have sent off for Cooper info. I'd guess that with deeper tread you'd get some squirming on bends on the road? That's the way it works with motorbikes anyway.

Light truck tyres sound sensible. How do they perform in the wet and in the snow, anyone know? (Yeah, I want my cake and ... ).

The CT rec'd pressure is 34 too, so thanks for the tip about dropping this as well.

Low is the go!
Just don't overheat them with too much speed.
The Munja Track to Walcott Inlet.

Cheers,
Peter
OKA196 Motorhome

Muddie, just gotta wear out what's on there first unfortunately. Good to see those Foz's out there.

P&M ... yep.

Just a follow-up ...

The Cooper info arrived and it says not to drop the pressure on std highway tyres cos they're not built for it.

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