[Dave]

I came across a discussion on the 4x4 forum where it was maintained that one should deflate one's tyres significantly (some went down to 0.3 bar)when travelling over rocks.
I have always kept my tyres inflated to prevent cutting the sidewalls.
What is the correct thing to do?
Dave

[Nick Gibson]

Deflate.

Someone once explained it to me by saying you should compare your tyres to a balloon, ie a fully inflated balloon pops easier than semi inflated balloon. So if your tyres are soft it will/should mould around the rock instead being pumped hard and not yeilding and getting cut.

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[Dave]

Thanks Nick.
Dave

[Bennvdm]

Hi

I think travelling over rocks should be defined better, as 0.3 bar sounds like a recipe to de-bead a tyre by turning to sharp, especially on offroad tyres with good grip. I would only go that low in extreme stuck in sand scenario & only drive straight to get out and then inflate a bit immediatly thereafter. Going that low will also significantly lower your vehicles ground clearance, increasing the chance of a rock damaging something.

I would therefor agree for more deflating where doing daytrip trail with unladen vehicle and drive very slow, but would not go to low with a fully laden vehicle - ie 1.5 bar on my old Lwb pajero did- sold Dec 13 & still looking...

Running 2.5 bar on gravel is allready to stiff, and reduces ride quality a lot & increase the forming of corrugations. Please note that I have 265/75r16 BFG muds & I do normally do gravel at 1.8 bar, but drive max 100 kph. It work good for me so far, as use Pajero mostly gravel&offroad. On the notorious Torra Baai road, there are loose rocks as sharp as I knife. Vehicles with tyres at 3.5 bar lost brand new BFG AT's, whilst I had no problem at 1.8 bar, driving in convoy. If corrugations are bad, I deflate even more, but drive a bit slower. The BFG's have a slightly thicker sidewall with 3ply, so may be a little less prone to sidewall damage than others.

The risk of sidewall puncture increases as deflate, but increases even more with speed. Most sidewall punctures I have seen were due to good gravel roads where drive 110-120kph and then have bad dips with sharp rocks and to little time to slow down sufficiently. Dips would not damage sidewalls if went through them at say 50kph, but problem at speed. Speed is usually therefor a greater factor than the size of tyre belly, but need to compensate with slower speed the bigger the belly.

I also do not travel at more then 60kph where deflated my tyres to 0.8 bar for sand driving etc & getting back onto tar road for short distances. Some tyres also debead easier than others, so I do not go easily go below 0.6 bar on my BFG muds, as they are known to debead easily. Most tyres are ok up to 0.5 bar in sand, but do not make sharp turns.

Regards
Bennie

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[Dave]

Thanks Bennie.
So it does look like deflating is the way go. I'd probably deflate down to 1.2 or at a push 1.0(I am normally heavily loaded)
Dave

[JohanV]

found 1.4 a very good comfy ride and no damage to tires. just take it slow. (loaded and empty)

You can see that even at 1.4 on the dewilt run, that the tire came close to de-bead and if it were rocks you might have the problem of rocks damaging the rim it self. you dont what the tire to pop like a balloon but you also dont want a piece of material offering no protection to the rims.

only in soft soft sand will i go down to 0.8. nothing lower unless you have beadlockers on the wheels.

trial and error. you will need to find a pressure that you feel comfortable with. Me and you dont load the vehicles the same so our needs are not the same.

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