MySwag.org The Off-road Camper Trailer Forum
General => General Discussion => Topic started by: stepheng on June 24, 2011, 08:58:13 PM
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One thing I have never been able to work out is the different tyre pressures, it seems people have different levels. What do people put there tyre pressures to on (cant think of any other type of terrain;
Bitumen
Gravel road
Sand
Mud
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36
26
never driven on sand
26
I'm sure there is already a thread on this...
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just keep pumping till the pump stops >:D
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Bitumen. 40 psi. 285x65x17
Gravel 24
Sand start on 16 and have been down to 12
Mud 24
Cheers
Carl
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Sorry forgot to add - do you also do the trailer to the same level as well or just leave them?
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Trailer I work out on footprint rather than pressure. I measure the width of the footprint on the rear tyres and match the width on the trailer.
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Sorry forgot to add - do you also do the trailer to the same level as well or just leave them?
I drop the pressures in the trailer also, but that just me
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on a serious note I run a trackbike and it's the most talk about topic in the shed
and one of the most important
there is no set and forget YOU MUST play around and work out the best for your vehicle and trailer then the next time you go out you will have more or less weight so it will need adjusting again
or set them all to about 32-35 watch for tyre wear and adjust in the soft sand drop them down enough to bag but not enough to come off the rims
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there is no set pressure guide you should work on all those terrains, it will vary on vehicle size and tyre size of each particular vehicle.
for things like sand...last year i had rears at 10psi and fronts at 8 psi to get over Big Red, everyone else before me running higher pressures failed to get over the dune no matter how hard they tried. different beaches / deserts have different sand on them, so some will be fine running say 20 psi - 22 psi but other beaches / deserts may require a lower pressure to be run.
gravel roads are the same, depends on how rocky / stoney the terrain is. so could be 25 psi if not all that rocky but could also be 20 psi if the terrain changes to be more sharp rocks about.
some people swear by the 4 psi rule, if you've never heard of it then have a read here...... http://www.aawen4x4.com.au/index.php?option=com_content&view=article&id=1:4psi-rule&catid=2:current&Itemid=7
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Trailer I work out on footprint rather than pressure. I measure the width of the footprint on the rear tyres and match the width on the trailer.
that's the best way of doing it, pressure alone is not a very accurate way of measuring traction, there are far to many variables (tyres brand/construction vs vehicle mass vs terrain) and it goes on but if you measure the foot print size you can work out what pressure best suits your set up.
me I've got a GQ patrol duel cab chop with alloy tray TB42 weight is about 2.35T empty, I'm running G/Y wrangler LT MTR kevlar in 33x12.5x15 on 10" rims, so on road 36psi, dirt/gravel 26psi, rocks/mud 18psi to start and go down to 15psi if needed. and well if i'm in the poo still thats what the winch is for ;D my CT only weighs about 600KG loaded by my calculations (still yet to put it over some scales) it's running 205x16R dunlop grippers LT (32x8 in the old language) on road 40psi and generally don't need to ajust them for off road work but at most in really heavy sand or mud I would go down to 24psi to start and as low as 18psi if it was needed.
hope this helps troy
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33" Maxxis Bighorns on a GQ LWB
40
32
18
22
For general 4wding outings I set to 22-25, 18 on the sand is a good starting point, but do remember a tyre will roll a bead if your not careful very easily at 18 or lower, no fast corners or swerving. It also depends on your tyres, I had some A/T 33" Cooper knock off's when I first got into 4wding that were horrible, Even on 25psi they would practically fall off the rim.
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I think the 4 psi rule is worth following. Another rule I heard was dropped the pressure until you rolled a tyre off the bead and then go up 1 psi! Well I got down to 8psi and never rolled a tyre. On my Hilux at 15 psi, I got a slow leak due to mud under the bead (at 15 psi) and went up to about 18. The long and the short is what you can get away with is a lot lower than you think!
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As everyone is saying.. it varies...
Ive been driving off road - or should I say off Highway for many years with some utter failures on tire performance along the way. Ive had low speed blowouts (underinflated and traveling too fast) bubbling of tire walls (tire failure due to pressure to high and/or too much load), bad wear and tear from different driving condtions etc...
There is no set and forget... nor is there a "this worked last time... lets do it this time" as conditions change, the load in your vehicle changes as does the type of tire you may be running and even some modifications may have an effect eg. suspension changes.
Its all about the comfort of the ride and how you feel as the vehicle is handling the environment.
Here is something to think about. Tire pressure directly relates to tire temperature. Tire pressure/temperature can adversly effect the tires longevity... I think that if a tire pressure is wrong (to soft) it increases the tire temperature and its this process that sees tires fail at high speed (often thought to be simply a blowout).
I think we all agree too high a tire pressure is not the desired solution, so its all about finding the most comfortable ride combining safety of the car and occupants, tire longevity (proper even wear), optimum fuel economy and then a comfortable ride (successful traction included).
So really its follow the suggestions of varied tire pressure as outlined by others in this thread and then seeing how it works for your rig.
Think of it this way.... a basket ball when pumped up to its recommended pressure will bounce nearly as high as from where you dropped it... whereas, the same ball with 5 - 10 psi less will struggle to bounce far at all.
directly relate that to tires.. the hard tire pressure (off road example) would require more assistance from your shock absorbers and suspension in general to try to keep the tire in contact with the ground reducing traction at high speed ie forest fire trails etc. Reduce the pressure by say 10 psi (or as suggested 30 or so psi) the tire is less likely to want to bounce and will there for give you more traction.. this better traction relates to a more comfortable ride.
Another thought when selecting tire pressure think of this very simple and crude .. yet very effective comparison. A childs birthday baloon.... when it has been inflated to resemble what we all know is a corectly inflated baloon is easily suseptible to bursting.. like poking it with a pen for instance. reduce the size of the baloon so it looks like it is under inflated, use the same pen with the same pressure to try to burst it.. ans see the results. It usually can withstand the same pressure and required significantly more pressure from that pen to burst it..
Relate that to tires... a tire can possibly be damaged or punctures easier if the pressure is too high, reduce that pressure and it can be argued that the same tire in the same situation may not have been punctured.... read carefuly... I said CAN be argued!
Ive escorted many vehicles across deserts on may occasions and was responsible for repairing the punctures that were had each day.... prior to me joining the company that I worked for, it was insisted that for the most part of each trip vehicles ran at 30 psi.. over everything... unless the guide asked for a different pressure. So we had vehicles of every discription traveling high speed dirt road over mainland Australia's interior at 30psi including the bituman legs if there were any short bits.. and the number of punctures reduced significantly. Sadely the puncutres were never iliminated... and at $300 - $500
per tire its not a great outcome in my opinion.
However, there are smarter ways to monitor tires nowadays and I have just installed a "sensatire" tire monitoring unit.
it measures tire pressure about 20 times per minute and tire temperature at the same level. this is done by a sensor that is fitted inside the rim. An audible alarm is heard if the any tire pressure falls or rises (whichever is applicable) outside of the set perrameters. Like wise the same alarm sounds if the temp varies outside the set perameters. There are two settings for driving. One is for highway cruising with its own specific perrameters and the other is for off road.
Simpe device, easy to set up, cheap to buy... I paid less than $150.00 posted free for mine and it cost the same as a strip and fit at your tire dealer to install. If it saves one tire its sooooo worth it!
Now I can SEE if my pressures are right or need adjusting.Now, if the temperature rises ti an unsatisfactory level I either have underinflated tires or I need to slow down to reduce the friction/resistance in rolling... an if I have a slow leak, I can see the tire pressure dropping before it starts to overheat.... being able to stop in a safe spot to inspect, repair or change the tire.
... and even around town its amazing to see the pressure vary depending on the time of day, duration of trip which tire is in sunlight and which has been in shade.. each tire pressure was set at the same time and I get a reading sometimes of more than 4 psi variation across 4 tires!
But.... this is a topic where everyone has an opinon... and I am positive there will be many who will disagree with parts of what I have just written.... but its food for thought.
good thread.....
interested in hearing how other people get along and how they manage to increase tire life whilst ensuring the vehicles ride is as comfortable as possible.
cheer
Alby
The pic is of the head unti of the sensor.... four readouts for four tires. Each read out corresponds to the location of the tire on the truck.
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Bitumen.. 34 front 38 rear solo 34 front 44 rear towing
Gravel road 24 F & R
Sand 18
Mud 18 if the day starts out wet, if it's only the occasional mud hole then the same as gravel 24.
Also I will adjust pressures sometimes to see if other pressures work better, some areas
terrains can require different pressures, but mostly I'll stick to the pressures above.
Baz.
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Bitumen 38 f. 42r
Gravel road 24 f 26 r
Sand 15 all round. Down to 5 in real soft beach work.
Mud 18 all round
We do quite a lot of beach and sandhill stuff down our way.
I'd love a carton of beer for every time I've either snatched out or helped tourists recover bogged vehicles on the soft beaches around here.( I'd be pi$$ed for a month).
Some of the most bogged vehicles are the ones with all the accessories on them (diff locks, big tyres etc).the drivers are more often than not reluctant to let tyre pressures go below 15psi.
In dead beach sand much lower pressures are needed.
:cheers:
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Bitumen - 35psi
Gravel - 35psi
Sand - 14psi
Mud - 14psi
I've done 70,000klm from my Goodyear MTR's which i bought new in 2004 and i have plenty left in them, although i'll probably replace them within the next 2 years. And i never rotate my tyres. ;) It's a lightweight jeep thing ;)
cheers
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I use the 4psi rule, and generally get a pretty good life frome tyres. (60-70k)
on road 36 psi
firm dirt rds 28-30psi
mud 20-22 psi
sand start at 20 and go from there.
but I would love one of those digital in car monitors.
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I think it depend how and where you drive. if you car is heavy or loaded you should use higher pressures on highway. We tend to usualy have the trailer hooked up when we travel longer distances, hence we use higher rear pressure.
Bitunem Front 40psi Rear 42psi
Gravel 32-34psi
Mud 24psi
Sand 22psi down. I have been down to 12-14 on several occasions. The rule I use for sand is keep dropping until I have decent grip.