Member Since: 28 Oct 2008
Location: Sydney
Posts: 38
Tyre pressures please
Trip to Lake Eyre and then Flinders Ranges next week. Lucky us!
Have just put Cooper st 245 70 17 on lr alloys on to replace the 18s, but am being given conflicting advice on the pressures to run on sealed and unsealed roads. The tyre placard on the car seems to indicate rather low pressures for the vehicle, especially loaded.
Any advice gratefully received as this is our first big trip.
Julia
26th May 2009 3:26 am
caverD3
Member Since: 03 Jul 2006
Location: Oberon, NSW
Posts: 6922
Had this problem when Bob Jane putb the Coopers on. Couldn't understand why the suspension had gone all harsh and was jumpin around on un-sealed roads. They had put then up to 40 psi.
LR figures are about right, I run slightly higher on the blacktop and slightly lower on unsealed and off-road. (28 front 34 rear)“There are only three sports: bullfighting, motor racing, and mountaineering; all the rest are merely gamesâ€
Ernest Hemmingway
D4 3.0 Active Diff, Adaptive Lights, High Beam Assist, Surround Cameras, Privacy Glass.
D3 2.7:Adaptive Headlights,Electronic Rear Diff,ARB Bar,Blaupunkt Speakers,JVC Powered Subwoofer,Removable Snorkel,Mitch Hitch,Pioneer After Market Head Unit,Steering Wheel Control Adaptor,Remote Adjustable Supension Rod System, Taxside Dual Battery System.
26th May 2009 8:18 am
rmp
Member Since: 15 Jan 2009
Location: Melbourne, Victoria
Posts: 73
Depends on the load and the terrain. Around the Flinders and Lake Eyre I'd go for 26psi on dirt roads. Onroad for high speed, loaded, 38. The tyre is different, therefore the pressure will be different. If those are LTs then add 2psi to each of the recommendations above.--
Robert
Life is better in low range
26th May 2009 9:37 am
Juliat
Member Since: 28 Oct 2008
Location: Sydney
Posts: 38
Thank you, much happier now.
Julia
26th May 2009 12:15 pm
rmp
Member Since: 15 Jan 2009
Location: Melbourne, Victoria
Posts: 73
Forgot to mention; keep the speed down on dirt roads with low pressures. Just because the D3 will easily do 100 on a dirt road doesn't mean to say it's sensible or safe.
Thing about dirt roads is it's not a matter of if they catch you out, it's when. I'm a big fan of cruising at 70-80 on the dirt for safety, enjoying the scenery and good fuel economy. There's times to go hard, but a touring trip isn't one of them.--
Robert
Life is better in low range
26th May 2009 12:18 pm
catweasel
Member Since: 05 May 2006
Location: Bundaleer
Posts: 4805
I would leave the pressures up at normal road pressures. no need to deflate you get no real benefit from doing so unless it is very sandy or muddy. some of the dirt roads can have more grip and be harder than the tarmac. deflate around the Flinders and you stand a much higher risk of a puncture. the only times Ive had punctures is when I decided to deflate (dont bother anymore and dont know why I did in the frst place) and they are usually terminal. 33 front and 38-40 rear load dependant.
26th May 2009 1:24 pm
stewmair
Member Since: 27 Jan 2007
Location: BENDIGO
Posts: 68
My experience, but with tyres other than Cooper's, is the same as catweasel's.
Sidewalls aren't built to drive on and a punctured tread is often repairable.
Don't deflate and drive slowly on stony roads.
It is said that at high speeds stones thrown up by the front tyres will chip the rear tyres at high speed (Cooper rep at RRCOAV meeting 2009). Seems to be a Cooper's problem of soft rubber.
Beware! There is a fashion at off-road driving courses to suggest deflation on rough roads!Cooper S/Ts, Dynamic 17x7s, Rotronics 3 way battery control, Boab drawers, Polaris camera, Mitch Bros tow, 4x4Intell wheel carrier and cargo barrier, Obie's rear wndow protector, Windcheetah roofrack, Featherlite rooftop tent, Faultmate, Trakmaster Nullabor 17. VK3PR VHF UHF.
Rover 75
27th May 2009 3:37 am
caverD3
Member Since: 03 Jul 2006
Location: Oberon, NSW
Posts: 6922
My experience has been the opposite. I got more punctures on unsealed roads at normal pressures and less when I lowered them a little and it gives a smoother ride. Maybe it depended on the tyre and how much the sidewall is exposed at lower pressures.“There are only three sports: bullfighting, motor racing, and mountaineering; all the rest are merely gamesâ€
Ernest Hemmingway
D4 3.0 Active Diff, Adaptive Lights, High Beam Assist, Surround Cameras, Privacy Glass.
D3 2.7:Adaptive Headlights,Electronic Rear Diff,ARB Bar,Blaupunkt Speakers,JVC Powered Subwoofer,Removable Snorkel,Mitch Hitch,Pioneer After Market Head Unit,Steering Wheel Control Adaptor,Remote Adjustable Supension Rod System, Taxside Dual Battery System.
Defiantly do not go higher than LR recommendations, and keep the speed down, much pleasanter trip, half the fun is getting there. Slowing down often means not ploughing into the local wildlife, who don’t obey the road rules, especially the mobile ant mounds that turn into camels and scare the hell out of you.
We were given all the conflicting advice re pressures and ended up doing LR pressures and all went much better towing a three ton van in the Kimberley’s and Pilbara.
Ryall
27th May 2009 4:01 am
smwilk
Member Since: 15 Oct 2006
Location: Gold Coast
Posts: 44
My LR dealer has always recommended 40PSI and they inflate to this at each service. Says they will wear too quickly at anything less?TDV6 D3 HSE
Previously D2 TD5
I'll second catweasel's comment, but on the OEM Wrangler ATs only. The sidewalls are so flimsy that they slice like bread. I now use Goodyear MTRs on sand (as WA beaches seem to have a bit of sharp-edged limestone in them ideal to slice sidewalls) and in about 5000km of sand or sharp rock there are a few bruises on the sidewalls but no damage at all. My conclusion is that highspeed tyres (V rated especially) are completely unsuitable for sharp edges but 3 ply sidewalls or other rugged, but lower-speed tyres can withstand much more sidewall impact. I use 45psi on the MTRs on the highway, 28-32psi on dirt, and down to 15psi on sand without a worry.Jim Dowell - D4 HSE TDi, 12,000 hydraulic winch & hidden winch mount, MTRs, TyreDog, Traxide 2 x aux battery system, fixed air compressor, Dolium roof rack, MitchHitch.
RIP 2005 D3 HSE V8 5 seater gold (stolen and torched)
27th May 2009 9:08 am
rmp
Member Since: 15 Jan 2009
Location: Melbourne, Victoria
Posts: 73
Guys there is a lot of misinformation in this thread. Any time anyone gives you a recommendation ask them to explain why and what evidence they have for it, tests run etc.
First point. Almost every tyre has a slightly different inflation pressure. Two tyres, one of LT and one of P construction will have different recommended pressures for the same weight. Go and consult the relevant charts if you like. I can explain why if necessary. Secondly the volume of air makes a difference, say a 275/40/20 has a lot less volume than a 265/65/17 so runs at a higher pressure. The weight of the car is another factor. As we generally run our cars heavier than stock with stronger tyres we'd be well advised to run greater than placard pressures which are for stock cars at average weight. Again, check out the charts from the tyre manufacturers if you want proof.
Secondly the effects of reducing pressure. To those that say it makes no differnece and isn't worth it; go find a dirt road and from 100kmph at 40psi do a full-on, emergency stop, ABS working overtime. Then same again running at 26psi. Then come back here and tell us the difference in average stopping distances. Do it three times as you'll find a variation on dirt.
Punctures. While you're playing with tyre pressures why don't you also find a rock about the size of a tennis ball. Drive up over it at 40psi. Notice how the tyre doesn't deform? Drop pressures to 26. Do the same. See the difference? Lower pressures mean the tyre deforms more readily around objects, reducing the chance of a puncture.
Then think about a balloon, blown up hard. Poke it with a biro and it'll burst. Drop some air out of it and it doesn't. Lower pressure, less puncture resistance. Also consider than lower pressures mean the tyre bounces less (technical term for that is hysteresis) which is good for traction and comfort, and less stress on the vehicle.
Speed is also a factor. Consider an axe, gently placed onto a block of wood. Will barely damage it. Consider same axe, swung at speed. Smash. Same deal with sharp rocks on dirt roads.
Sidewalls. Go and actually measure how far the sidewall extends at 40psi and 26. It's tiny. And remember it's also harder to puncture with less air in it. The whole sidewall-damage-at-low-psi theory has never been supported with any proper evidence I've seen, only a few people saying they had damage at low pressures; who's to say it wouldn't happen at higher?
Yes high-speed rated tyres are a complete disaster in the bush, that's spot on. Quick reason -- they have to dissipate so much heat at speed they have a very flimsy construction.
Higher than LR recommendations. Well, if your tyres are changed the placard is out the window, and the placard is only a guide anyway. What you shouldn't exceed is the max-inflation on the side of the tyre.
Sidewalls aren't built to drive on. Correct. Let a tyre down to 10psi and you'll note the sidewall doesn't even touch the ground.
All those offroad instructors who advocate lower pressures? And the tyre people? And the likes of the Plates at Pink Roadhouse? Do you really think we're all wrong? We might be, but let's have the proof before you say high psi on the dirt is a good idea. I'll change my mind when I see the proof. It's not a fashion, it's advice borne out of solid logic and hard experience.--
Robert
Life is better in low range
27th May 2009 10:11 am
caverD3
Member Since: 03 Jul 2006
Location: Oberon, NSW
Posts: 6922
Agree, a good argument, but the problem with sidewall damage with low pressures comes when you turn and the tyre rolls exposing the sidewall to impact.
I think you meant higher pucture resistance:
"Then think about a balloon, blown up hard. Poke it with a biro and it'll burst. Drop some air out of it and it doesn't. Lower pressure, less puncture resistance. Also consider than lower pressures mean the tyre bounces less (technical term for that is hysteresis) which is good for traction and comfort, and less stress on the vehicle."“There are only three sports: bullfighting, motor racing, and mountaineering; all the rest are merely gamesâ€
Ernest Hemmingway
D4 3.0 Active Diff, Adaptive Lights, High Beam Assist, Surround Cameras, Privacy Glass.
D3 2.7:Adaptive Headlights,Electronic Rear Diff,ARB Bar,Blaupunkt Speakers,JVC Powered Subwoofer,Removable Snorkel,Mitch Hitch,Pioneer After Market Head Unit,Steering Wheel Control Adaptor,Remote Adjustable Supension Rod System, Taxside Dual Battery System.
27th May 2009 10:36 am
rmp
Member Since: 15 Jan 2009
Location: Melbourne, Victoria
Posts: 73
caverD3 wrote:
Agree, a good argument, but the problem with sidewall damage with low pressures comes when you turn and the tyre rolls exposing the sidewall to impact.
I think you meant higher pucture resistance:
"Then think about a balloon, blown up hard. Poke it with a biro and it'll burst. Drop some air out of it and it doesn't. Lower pressure, less puncture resistance. Also consider than lower pressures mean the tyre bounces less (technical term for that is hysteresis) which is good for traction and comfort, and less stress on the vehicle."
Sorry yes! Got it backwards.
When you turn the sidewall still doesn't hit the ground.--
Robert
Life is better in low range
27th May 2009 10:44 am
catweasel
Member Since: 05 May 2006
Location: Bundaleer
Posts: 4805
all very nice but the ballon theory is not comparing apples with apples and very simplistic. my comments were based on the wranglers, grabbers and current cooper ht plus and the fact that the Flinders was specifically mentioned and that is my usual playground. as for 40 psi where is that recommended except in the rear and when fully loaded and if you have large rocks you drive accordingly. I find no difference between road and reduced pressures. never lowered them in the Commodore and once never suffered a puncture and thats been most places a 4wd would most likely go. also the Grabber sidewalls are no better than the wranglers in my opinion just tread wear is better and will not purchase them again.
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They had put then up to 40 psi. 
