Tyre Pressures

[gu4800]

Following from another thread, I have a general question about tyre pressures.

On the "other" thread, someone had a massive tyre blowout for one reason or another (I don't want to get into the arguement on the other thread - please). It was suggested that the tyre may have been run at low pressures for an extended period. My question:

I am going up to Fraser next week for the week. I usually drop the pressure to 18psi. I will be driving on hard sand for about 1hr (60 klm's) at about 60 - 80 kph. Is this bad? Could I potentially damage the tyre as suggested above by running for an extended period on a hard surface at 18psi? Or is there enough "give" in the sand (even the hard sand) to make this OK?

Thanks for the advice.

[-Scott-]

In my limited experience I'd be nervous about running the weight of a GU on 18psi at 80km/h.

The surface has very little to do with it. The big issue is the sidewall flex as the tyre rotates. At low pressures, any given section of the sidewall is bowed out as it passes underneath the rim (and is trying to support the weight of the vehicle.) As this section then passes up and over the top, it straightens out again. So the sidewall continually bends and straightens and bends and straightens and bends and...

It's this continuous cyclical flexing which is really the problem. It generates heat, and it's the heat which kills the tyres. Speed is the biggest contributor, because higher speed means more cycles in any give time period. Weight sucks, because more weight means more bend. Hot weather doesn't help, and hot bitumen heats tyres at the best of times.

If you can't get away with higher pressure for that first hour or so (25psi?) then take it easier up the beach - windows down, enjoy the fresh air and cruise at 60km/h.

Enjoy Fraser - I did.

Scott

[gu4800]

Thanks for the tip - makes sense. 25psi up the beach it is (down to 18psi once I reach camp).

Oh, and don't worry about enjoying Fraser - I DO! Every year, same week (Ekka week). Never miss it.

Thanks again.

[twinnie]

at 18psi don't yu risk losing a tire off the wheel?

Matt

[HeathGQ]

at 18psi don't yu risk losing a tire off the wheel?

Matt

at 80 k's on hard sand, yeah. I would follow on teh same lines as above. Tyre pressures are all relevant... tyre, vehicle, load, surface. Look at the load your carrying to go to Fraser for the week? 18 is too low, 25 should be your starting point.

And we are heading over for a week in September

[DamTriton]

The other cheaper option is to get yourself a decent compressor, basically for about the same cost as the next tyre you are going to trash by running low pressures on hard surfaces/at speed.

The benefit is even if you lose a bead on the beach due to low tyre pressures, all things being equal, you should be able to reseat the bead with the wheel still on the vehicle. Ever tried jacking a 2 1/2 ton vehicle up to change a tyre in soft sand??? This would be your only option otherwise..........

After your day is done, you can pump up all your tyres to a more appropriate pressure.

"An ounce of prevention is worth a pound of cure"

[Cossie]

The other cheaper option is to get yourself a decent compressor, basically for about the same cost as the next tyre you are going to trash by running low pressures on hard surfaces/at speed.

The benefit is even if you lose a bead on the beach due to low tyre pressures, all things being equal, you should be able to reseat the bead with the wheel still on the vehicle. Ever tried jacking a 2 1/2 ton vehicle up to change a tyre in soft sand??? This would be your only option otherwise..........

After your day is done, you can pump up all your tyres to a more appropriate pressure.

"An ounce of prevention is worth a pound of cure"

I agree with what you're saying but you aint gonna re-seat a bead without jacking the vehicle up anyway!

[gu4800]

The other cheaper option is to get yourself a decent compressor, basically for about the same cost as the next tyre you are going to trash by running low pressures on hard surfaces/at speed.

The benefit is even if you lose a bead on the beach due to low tyre pressures, all things being equal, you should be able to reseat the bead with the wheel still on the vehicle. Ever tried jacking a 2 1/2 ton vehicle up to change a tyre in soft sand??? This would be your only option otherwise..........

After your day is done, you can pump up all your tyres to a more appropriate pressure.

"An ounce of prevention is worth a pound of cure"

Got the compressor. Will be going by the above and run 25 up and down the beach. Can always air down for the softer stuff, and then air back up for the drive back down the beach on the trip home.

Thanks again for the advice guys.

[customhilux]

i always let mine down to 8psi, even drive home doin 80k's,

never rolled one and never blown one.

[jeep97tj]

But how much bag do u have in your tyres?? i think a fully loaded wagon with 16psi would have a fair bit of bagging and that is what kills the tyres.

[Gribble]

Just to throw a spanner in, isn't running road-like pressures on sand considered as eco-violence to the beach? The only 2 times my ute has graced the sand i ran 15psi and had no dramas at all with heating up tires, never went over 80k's though.

[-Scott-]

i always let mine down to 8psi, even drive home doin 80k's,

never rolled one and never blown one.

And when you have an accident at 80km/h on 8psi, you're handing your insurance company an excellent opportunity to laugh at you.

Just to throw a spanner in, isn't running road-like pressures on sand considered as eco-violence to the beach? The only 2 times my ute has graced the sand i ran 15psi and had no dramas at all with heating up tires, never went over 80k's though.

It's not so much the pressure you run as the amount of digging you do. More aggressive tyres will dig more at highway pressures: the H/T tyres on my Paj when I bought it laughed at sand at highway pressures, the S/Ts dug like crazy at the same pressures.

Vehicle weight also plays a part. My Paj is about 1700kg empty, and I'm happy to cruise at 80km/h on 20psi. What's a GU weigh? 2500kg+?

As for heating tyres, how did you measure the temperature? The best indicator is to measure tyre pressures cold, and after cruising at speed. Basic physics tells us a 10% increase in pressure basically means a 10% increase in air temperature in the tyre. Remembering to calculate temperature in Kelvin, not Degrees C, that would be around a 30 degree temperature increase. Starting with 20psi at 23 Deg C, if your pressures climb to 25psi the air inside your tyres is somewhere in the vicinity of 100 Deg C.

Don't believe me? The rubber outside the tyre is radiating heat OUT of the tyre, so it will be cooler than the rubber inside - you can't tell by that.

Let some air out to feel it's temperature? As the air expands, it cools - that's how a refrigerated cooling system works. You can't tell that way.

Reduce your pressures, reduce your speed! What's so hard about that?

Scott

[customhilux]

i always let mine down to 8psi, even drive home doin 80k's,

never rolled one and never blown one.

And when you have an accident at 80km/h on 8psi, you're handing your insurance company an excellent opportunity to laugh at you.

i'll just play dumb, the man at the servo filled them up for me. but by the way, on 8psi u don't drive like a dick head and ya fine,

but runnin MT/r's on the beach they dig bad, i have my stauns set at 8psi,

i use that for rock, sand everything

jeep97tj

But how much bag do u have in your tyres?? i think a fully loaded wagon with 16psi would have a fair bit of bagging and that is what kills the tyres.

thats what i want, it spreads the load, so it doesn't dig as much.

as above i've got MT/r's and they bag but are still solid.

[-Scott-]

i'll just play dumb, the man at the servo filled them up for me. but by the way, on 8psi u don't drive like a dick head and ya fine,

It doesn't have to be your fault. Consider this:

You're cruising along at 80km/h on your 8 psi. Some hat-wearing fossil in a commuter crumple-car forgets this whole "give way" thing and pulls out 50 metres in front of you.

Instinctive reaction: you stomp on the brakes - but not too hard, because you're good, and you want to steer around him too. You turn the wheel, but the sidewalls elect not to play, and your front left tyre pops off the bead.

Plough understeer, accident. Fossil's insurance company assessor decides the accident could have been avoided had your tyres not fallen off the rim (gravel rash on your sidewall tells a nasty story - do you have that pretty white outline lettering?) Assessor jumps on Outer Limits 4x4, uses the Search function (some of these assessor types are smart enough to make it work ) and finds pages of opinions that your tyres will roll off the rims below 12/15/16/18 psi. They start thinking negligence, start thinking you're at least partially to blame for the accident. So you wear part of the cost.

Your insurance company now wants to haggle about who's paying. And they're haggling with you.

But you're right. You'll never have an accident if you drive sensibly. I haven't. Except the time I was run off the road. Up a bank, hit a tree and rolled my car. My insurance company even agreed it wasn't my fault - lucky me!

YMMV

Scott

[customhilux]

i'll just play dumb, the man at the servo filled them up for me. but by the way, on 8psi u don't drive like a dick head and ya fine,

It doesn't have to be your fault. Consider this:

You're cruising along at 80km/h on your 8 psi. Some hat-wearing fossil in a commuter crumple-car forgets this whole "give way" thing and pulls out 50 metres in front of you.

Instinctive reaction: you stomp on the brakes - but not too hard, because you're good, and you want to steer around him too. You turn the wheel, but the sidewalls elect not to play, and your front left tyre pops off the bead.

Plough understeer, accident. Fossil's insurance company assessor decides the accident could have been avoided had your tyres not fallen off the rim (gravel rash on your sidewall tells a nasty story - do you have that pretty white outline lettering?) Assessor jumps on Outer Limits 4x4, uses the Search function (some of these assessor types are smart enough to make it work ) and finds pages of opinions that your tyres will roll off the rims below 12/15/16/18 psi. They start thinking negligence, start thinking you're at least partially to blame for the accident. So you wear part of the cost.

Your insurance company now wants to haggle about who's paying. And they're haggling with you.

But you're right. You'll never have an accident if you drive sensibly. I haven't. Except the time I was run off the road. Up a bank, hit a tree and rolled my car. My insurance company even agreed it wasn't my fault - lucky me!

YMMV

Scott

yeah good on u,

i've also been taken out on the high way by a B double.

well if u can locate an outers sticker on my truck, then i'll pay for your next tyre's.

so what mod's u got on your car, because if it's anything other than standard and not engineered, then they can also wipe u, or if u have changed the wheels legal or not and not notified them about the change, wipe again.

[Hoonz]

thats how i got my MTRs really soft .. ran them at 5psi for an hour when i got them worked awesome ever since spesh on rocks

tsv crew can vouch for the awesome bagging offroad

[-Scott-]

yeah good on u,

i've also been taken out on the high way by a B double.

well if u can locate an outers sticker on my truck, then i'll pay for your next tyre's.

so what mod's u got on your car, because if it's anything other than standard and not engineered, then they can also wipe u, or if u have changed the wheels legal or not and not notified them about the change, wipe again.

We all take our chances with the mods on our trucks, based on what should be educated decisions. Every modification to my vehicle is on my insurance policy.

You come into a discussion on tyre pressures advocating running 8psi at 80km/h, because you drive carefully and you'll be OK. It's not necessarily your driving which will cause an accident.

I'm trying to make it clear to anybody following this thread that I think what you are doing is dangerous, and if anybody decides to do the same as you they should understand the implications.

You do what you like with your vehicle. If you're going to give advice be prepared to have it challenged.

Scott

[bazzle]

i always let mine down to 8psi, even drive home doin 80k's,

never rolled one and never blown one.

I used to use 15 psi on 33's with no problems . 6 trips and a few days each,
many more on north shore, a few in the big desert, some fast up the beach other inland .
Never rolled a bead, just dont try doing a fast "Uey"

Bazzle

[patrolman]

i never used to pump the tyres up after a trip, so they would stay at about 18-20 psi till a week or so later and never had any problems

[Major60]

Adopt the Michelin 2PSI rule on sand, gravel, highway and you can't go wrong with pressures. Auto calibrates for the loaded weight of the vehicle, speed, heat etc.

[customhilux]

yeah good on u,

i've also been taken out on the high way by a B double.

well if u can locate an outers sticker on my truck, then i'll pay for your next tyre's.

so what mod's u got on your car, because if it's anything other than standard and not engineered, then they can also wipe u, or if u have changed the wheels legal or not and not notified them about the change, wipe again.

We all take our chances with the mods on our trucks, based on what should be educated decisions. Every modification to my vehicle is on my insurance policy.

hard to believe that, unless it's stock.

You come into a discussion on tyre pressures advocating running 8psi at 80km/h, because you drive carefully and you'll be OK. It's not necessarily your driving which will cause an accident.

same go's with u runnin 80k's up the beach, just as dangerous if more, the beach changes all the time.

I'm trying to make it clear to anybody following this thread that I think what you are doing is dangerous, and if anybody decides to do the same as you they should understand the implications.

right back at ya, driving on the beach at 80k's is a dangerous thing to do. u can't avoid something as easy as u could on the road,

You do what you like with your vehicle. If you're going to give advice be prepared to have it challenged.

once again, right back at ya, dude my truck weigh's more than yours but, u seem to think that running 18psi is nerve racking, well if thats the case stick to your hardcore sand driving then.

It's not so much the pressure you run as the amount of digging you do. More aggressive tyres will dig more at highway pressures: the H/T tyres on my Paj when I bought it laughed at sand at highway pressures, the S/Ts dug like crazy at the same pressures.

dude u just contradicted yourself there,

it does matter what pressure u run, on lavis lane on stocko beach, mine wont go anywhere without goin down to around 10psi, the less tread spreads the load more, causing it to compact the sand rather than dig in, as more aggresive tread will do,

sorry gu4800

u can have your thread back, i was just showing an example on pressure's earlier, but NJ SWB had to have a cry about it, but i think he should be done,

anyway gu4800, have fun on ya trip.

[Dodger]

Isn't it all about driving to the conditions.
If the sand is real soft then low pressures are the go.
If the sand is hard then 20 to 25 is the go.
If the sand is soft in places then 18 is the go.

At all times less than 80kph should be the go.



Just my thoughts.

[Maxtd5def]

[quote="gu4800"]Following from another thread, I have a general question about tyre pressures.

On the "other" thread, someone had a massive tyre blowout for one reason or another (I don't want to get into the arguement on the other thread - please). It was suggested that the tyre may have been run at low pressures for an extended period. My question:

I am going up to Fraser next week for the week. I usually drop the pressure to 18psi. I will be driving on hard sand for about 1hr (60 klm's) at about 60 - 80 kph. Is this bad? Could I potentially damage the tyre as suggested above by running for an extended period on a hard surface at 18psi? Or is there enough "give" in the sand (even the hard sand) to make this OK?

Why not just check them every now and then. Stick your hand on the tread. You'll soon get to know whether they're too hot or not.

Its something I do on a trip, particularly with a trailer on - every cuppa stop, just walk around & feel them. You'll soon know if one's going down, or too low, without a gauge.


Regards
Max P

[Zute]

customhilux, you are a fool. Stop being lazy and put air in your tyres when you hit the road. Thats what the valve is for. Your playing Russian roulette with other peoples lives.

[customhilux]

customhilux, you are a fool. Stop being lazy and put air in your tyres when you hit the road. Thats what the valve is for. Your playing Russian roulette with other peoples lives.

wake up loser, read ya sig line

Brakes, who needs them?
They only slow you down.

[TakeTwo]

Seriously kids. It was a simple question turned into a biatch fight.

The media is playing against 4 wheelers at the moment and your attitudes are proving them right.

[-Scott-]

We all take our chances with the mods on our trucks, based on what should be educated decisions. Every modification to my vehicle is on my insurance policy.

hard to believe that, unless it's stock.

What's so hard to believe about that? I've listed all my modifications with my insurance company.

You come into a discussion on tyre pressures advocating running 8psi at 80km/h, because you drive carefully and you'll be OK. It's not necessarily your driving which will cause an accident.

same go's with u runnin 80k's up the beach, just as dangerous if more, the beach changes all the time.

Don't change the subject. This started with you advocating 80km/h on public roads at 8psi. I drive to conditions, including tyre pressures. You don't.

I'm trying to make it clear to anybody following this thread that I think what you are doing is dangerous, and if anybody decides to do the same as you they should understand the implications.

right back at ya, driving on the beach at 80k's is a dangerous thing to do. u can't avoid something as easy as u could on the road,

You're changing the subject again. Your vehicle at 80km/h on 8 psi is dangerous - to you and others.

You do what you like with your vehicle. If you're going to give advice be prepared to have it challenged.

once again, right back at ya, dude my truck weigh's more than yours but, u seem to think that running 18psi is nerve racking,

Who said nerve-wracking? I believe it's dangerous running 80 km/h with 18psi in a (presumably loaded) GU Patrol. It's the combination of low pressure and high speed which is dangerous. There's nothing particularly dangerous about 18psi - if you drive suitably.

well if thats the case stick to your hardcore sand driving then.

It's not so much the pressure you run as the amount of digging you do. More aggressive tyres will dig more at highway pressures: the H/T tyres on my Paj when I bought it laughed at sand at highway pressures, the S/Ts dug like crazy at the same pressures.

dude u just contradicted yourself there,

it does matter what pressure u run, on lavis lane on stocko beach, mine wont go anywhere without goin down to around 10psi, the less tread spreads the load more, causing it to compact the sand rather than dig in, as more aggresive tread will do,

Isn't that what I wrote? More aggressive tyres will need lower pressures.

sorry gu4800

u can have your thread back, i was just showing an example on pressure's earlier, but NJ SWB had to have a cry about it, but i think he should be done,

You think? There's a first...

You gave an example of a dangerous practice and you're struggling to defend it by accusing me of being dangerous too.

What's next? Name calling?

Scott

[bigpat]

Got back Friday from QLD, including a days play on Fraser.

I had my Surf absolutely fully loaded including roof rack. Ran my Simex M/T's at 25 psi and they were fine cruising around the inner tracks, and the beach at up to 60 km/h.

You shouldn't have to drive quicker than that, although a couple heroes do( including the idiot tour bus drivers )

Although the tyre heats up due to flex, it is always cooled by the damp sand.

Stick to 22-25 psi, 60-65 kays tops, and enjoy your drive......

[Adomw]

Dude,

Tyre heat is the killer here - why don't you experiment a bit as it's all dependant on the tyre and the load on it

do your fanging around at 80k and 20psi, stop and put your hand on the side wall - see if its hot if you can keep your hand on the rubber then you'll be fine..,

my experience in Lucky Bay ( near Kalbarri WA) on the dunes is that 18-20psi gets me everywhere with no appreciable increase in tyre heat - but 10psi warms up abit but I can still touch the tyre

I've never rolled a tyre off - or had a blow out


One other trick - if you are getting significant tyre heat the tyre pressure will go up so when you getout to feel the tyre check the pressure again
if the pressure has gone up the air inside is getting hot and increasing the pressure (boyles law)

Ado