Tyre presssures over rocks??

[A.J.M]

Going to throw this one out there to get some info/real world examples as plenty of you US based people get the chance to do serious rock crawlling.

I was taking my D3 (LR3 to others ) around some lanes on Monday and Tuesday with Defender driving mates. One lane we did is very rocky and even though i've driven it before without incident with the same tyres.
This time i suffered a blow out half way up the lane. It was a front left tyre that let go. The inner sidewall blew out with a hole large enough to put a thumb into.
Tyres are Goodyear Duratrac's in 19 inch size.

I had the pressures set at 38psi all round. I've ran that pressure before and had no issues, i've used the car in every terrain bar sand at that pressure and have not suffered because of it.

Now. The lane does have sharp rock areas along it's length and the area i was on when it let go didn't have any sharp bit's that the group could see to be the main reason for the failure so could have been damaged earlier and driven on till it failed.

I've been told that i should have lowered my pressures to 15psi max and driven over the rocks in that way.

I'll be very honest and say, i have only been doing this off road driving for 2 years and i've only been driving for 10 years, i'm 27 and passed at 17 which is when you can learn in the UK. So i'm not sure if that info is correct or wrong.

No one in the Defender's lowered their pressures or suffered failures. My car was being used as the supply/back up truck and was loaded accordingly and had 4 people in it.

What would you have done?

I can get pictures of the lane in question if that would help give more info/answers.

 

[DVD]

Here's a youtube vid by somebody well respected who suggests not airing down in LR3/4, Disco3/4 - even airing up - for offroad trails when using our 18 or 19 in rims.
https://www.youtube.com/watch?v=a81JPyo7J50

I have 18s and typically don't air down, or if I do, it's to 33 / 38. The ride is pretty soft regardless, and traction control is great, so it works out OK. The exception is sand, and then I go down to 18.

Opinions seem to be all over on this topic for our vehicles.

 

[summerprophet]

The primary reasons to air down, are better traction, and better driver comfort. With 19" rims, you don't have a huge amount of sidewall, so airing down too much exposes your rims to possible damage.

In your case, not knowing how your tires air down, or the specifics of the trail type, I would hesitate to suggest airing down, unless you find yourself breaking traction lots.

Always a good suggestion for deep snow however.

 

[A.J.M]

Ok. That D4 has 19s and General AT's fitted.
He has the pressures at 3 bar. Now a bar is 14.5psi so that's 43.5psi he ran them at...

That's interesting. His terrain was more rocky than what i drove over as well.

 

[newhue]

Its an old analogy, but think of your tyres the same as a balloon at a kids party. Up hard or full they pop very easy, but at 1/3 volume they can kick around the yard all day no matter who jumps on them.

I'd also imagine, if one if concerned with a bit of damage or scratching on their rims, perhaps another past time pursuit should be considered. Or perhaps every couple years send the wheels in to be fixed and buffed, it's probably the same cost as a tyre or two anyway.

 

[shogun]

Goodyear. Thats a large part of the problem. Never again.

 

[A.J.M]

Some varied answers so far, also a pm. I will reply to you soon sir.

Here's a few pictures of the car on the lane leading up to the blowout.

Hole in the tyre, I patted the sidewall back in a bit.

Where it went. Couldn't roll it backwords or forwards as it was on a small plateau between climbs.
As an aside, I found out that opening the pass door and using a hi lift jack on the tree sliders can lift the full side of the car up.
That's me standing and looking at it with mild annoyance...

Out of curiosity, why is Goodyear part of the issue?

 

[Mack73]

Out of curiosity, why is Goodyear part of the issue?

The duratrac only has a 2 ply side wall. It is a known weakness and not good on sharp rocks.
Want to see some more duratracs with holes in the sidewall? https://www.google.com/search?q=dur...bCiQLQ34DAAg&ved=0CAkQ_AUoAg&biw=1350&bih=625

 

[JIMBO]

:sombrero: Well, to me it looks like your drivers side front tire just "scraped" the RIDGE of one of those bigger rocks and much lower tire pressure may have saved it--but

A little more drivers attention to the terrain, in relation to your tires---

I don't airdown either--just use a 6th sense for "EDGED" rocks-and

Goodyear has been making top quality tires for almost 100 years--it wasn't the tire, or mfg-

Good luck

:costumed-smiley-007:bike_rider: JIMBO

 

[Red90]

Airing down to the correct pressure is better for preventing punctures. The Duratrac do have a reputation for weak sidewalls.

As far as "correct" pressure. Measure the sidewall height at road pressure. Air down until the sidewall is 75% of that height. That is your minimum general safe pressure to run at. You can't just choose a pressure as different tire sizes and vehicle weights make a big difference in what is safe. As far as I'm concerned everyone should always air down off road. It is safer and the upsides outweigh the downside by a large margin.

 

[charlieaarons]

I don't think airing down would have significantly decreased the risk of a rip like that. Sooner or later on terrain like that it was inevitable with short weak sidewalls like that.
A tire like this:
https://www.vrakking-tires.com/stock/16-inch/653-50r16-michelin-xzl-new.html
would have held up. However, I have no idea if a 16" rim fits your vehicle, also no idea if a tire 1.5-2.0" taller would fit. Vrakking also sells a 7.00R16 Uniroyal T9, probably just 1" taller than your tires, and likely to have steel sidewalls (like the Michelins).
Michelin also make "XPS Rib" and XPS Traction" in 16" rim, ranging from 29.6" dia. to 32.0"
https://www.vrakking-tires.com/stock/attachment.php?id_attachment=14

Charlie

 

[A.J.M]

Due to brake callipers I'm using 19s as they are realistically the only wheel that will fit.
I could get a set of compomotive pd1880/1 alloys which are 18s, but they are over £250 a wheel and I would need 5. Then 5 tyres. Not an option I can afford.

My usual off road conditions are muddy wet grassy areas, with no real rock crawl areas in it.
The lanes we did are in England as no lanes exist in Scotland.

I also use a mate for being my spotter for the more interesting parts, sometimes 2 to help keep the car away from the sharper rocks.

I now need a replacement set of tyres, that have to cope with everything. Lots of road miles in wet and dry conditions, snow and ice, mud, grass, gravel. Pretty much all terrains..

So, what's people's thoughts on that one?

The tyres I have are 255/55/19 profile and will be going onto a set of 6 spoke HSE rims.

 

[Scoutn79]

As other mentioned with the size rims and tires you are running you can't do much airing down.
You might be able to go down to 25 or 30 to soften the ride some but it likely isn't going to get you much of a benefit on a vehicle that light.

Darrell

 

[nwoods]

I agree that GoodForOneYear's were part if the problem. Duratrak's have a nice tread pattern, but not a very durable carcass. I have led several groups lately, and have experienced 3 flat tires in my group, two were Duratracks, one was a set of MTR's (which did surprise me actually, as I think the MTR is a decent tire, but shred it did!)

On my LR3 with 18" wheels, I typically aired down to 24 PSI. 19" wheels, I'd probably only go down to 30psi in that sort of pebbly terrain. There's just not very much sidewall to get much wrap around conformance on a 19" wheel.

Did you have any issues deploying the spare from underneath in that scenario?

 

[newhue]

Not sure if they make your size, but I'll chuck my hat in on BFG.
I have run these tyres on 15psi at 3.5T for weeks on end, and over several trips. I have done hour upon hour at 50Mile/h on 23 and 26psi at 3.5T over corrugations; running over the occasional base ball sized rock amongst the endless gold balls sized. They are my daily driver tyres in the city on a 2.5T truck, and have been on for 43K mile and expect to get another 20 out of them. I love em. They are muds however. I don't fns they noisy but understand if others do.

Check for sorts of tyres here http://http://www.tirerack.com

Check you tyre radius here for what will fit under the guards and legalities.
http://www.exploroz.com/Vehicle/Tyres/SizeCalc.aspx