4PSI RULE - Tyre Pressures

Advice on the right rolling stock for your 4WD
Peter Aawen
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Re: 4PSI RULE - Tyre Pressures

Unread post by Peter Aawen » November 12th, 2011, 7:23 pm

Check out the Tips & Techniques article in 4WD Action, Issue 172, Page 81 - Turn the Pressure Down.
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gqjay
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Re: 4PSI RULE - Tyre Pressures

Unread post by gqjay » November 28th, 2011, 12:43 pm

Im not convinced but will give it ago.

whats are the chances if i go for a drive on the HWY for hour.Sun beaming down on the passenger side, would the drivers side be cooler, and will this affect what pressure what is needed.... And then if it rains or driving at night on cooler roads will I need to adjust the pressure again on a fine day or during the day to get max life out of the tyre....
Or am I looking into this to much and find the average psi and go from there...

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Re: 4PSI RULE - Tyre Pressures

Unread post by Peter Aawen » November 28th, 2011, 1:26 pm

You will find that there are minor differences introduced by weather/ambient temps etc, but generally the biggest differences in tyre pressure will be from significant changes in the surface you are driving on, the speed you are travelling at, and the loads you are carrying. So while loaded up & travelling at Hwy speeds in the Tropics will usually warrant a fairly different pressure than stop start driving to work thru the 'burbs on your way to work in the rain, unless there is a significant difference in those major factors, then generally any 'average' you work out is going to be so close to the same it won't make a real difference.

But try it, the more effort you spend in 'getting it right' and learning to understand what speed, weather, temp, & load variations make to the 'optimum' pressures for your tyres with you driving, the better you'll be able to apply that knowledge to getting the best from your tyres. A little effort early in the piece will generally see you being able to make an educated guess at what sort of pressure is going to be pretty close to right, then after an hours driving or so you only need to check your pressures to see how close you were & maybe add or lose some air to 'fine tune' it. The guys from Coopers & Mickey T as well as the Mag article are now recommending that you keep a 'log book' of those things & the pressures you started with, plus what changes you made so you can look back on it later; that can be a great way of confirming and learning fairly quickly, altho we haven't found too many that take more than a few weeks of reasonably diligent practice at using it to get it down pat.

And remember the 4psi rule's a guide that gives you a way of doing all this 'tyre pressure' stuff basically the same way every time, but you also have control over your driving style, how hard you brake, how hard you corner, what loads you carry, how fast you drive, what type/size tyres you run, etc - and changing any one of those significantly can also vary the 'optimum' tyre pressure for what you are doing right now. So checking your tyre pressures after an hour's driving is always a good idea, giving you an opportunity to 'fine tune' your start pressures & ultimately getting the best from your tyres.
An Ex-Service person is someone who thought enough about their country & how great it is, how lucky we are to live here, to write a blank cheque made out to 'The People and Commonwealth of Australia' for the value of 'Up to & including my Life!'

harts
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Re: 4PSI RULE - Tyre Pressures

Unread post by harts » December 3rd, 2011, 4:04 pm

i havn't read the whole thread so this may have come up already but here i go....

Tyre rubber starts seperating about 2-3years after manufacturing them. This will change of course dependant on the amount of time they see the sun and many other varying factors.
So, say i use the 4psi rule and all of a sudden i am getting 90 000km out of my tyres, while i still do less than 20 000km/ year, isnt the rubber actually very much deteriorated and i am putting my vehicle/passengers at risk with harder/non 'sticky'/seperating tyres?

The way i see it is i have to replace my tyres every 2-3 years. So if i did say 30 000+ km a year then the 4psi rule would be very handy but seeing as i do about half that it is handy but not very useful to me as i wont actually save any money due to replacing tyres anyway?

Let me know what you all think :)

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Re: 4PSI RULE - Tyre Pressures

Unread post by Peter Aawen » December 3rd, 2011, 4:43 pm

You'll still get better ride, handling, fuel economy, and traction from your tyres by running the 'right' pressures than you would by running pressures too high or too low - plus you won't be damaging the tyres so much and accelerating that 'aging' so they might actually last as long as you keep them on the car for maybe 5 years instead of having them deteriorate to useless after only 2-3.

Tyres on your vehicle are generally considered to have a usable life of around 5 or so years if you look after them reasonably and don't wear them out first. (check with the manufacturer re the date stamp on their tyres & tyre life) But as they age they do tend to get harder, and harder tyres generate heat quicker, so applying the 4psi rule will see you running a (slightly?) lower pressure on older/harder tyres so that they work just as well as they did when they were new.... altho once they are over a few years old they may well get to the stage that no matter what pressure you run in them they never provide reasonable traction, but that's fairly noticeable to most competent drivers and a sure sign that if you want to remain safe it's past time to fit new tyres!! ;)

So even you might almost double the 'life' in years as well as kms that you get from your tyres by paying attention to running the right tyre pressures, and you'll benefit in other ways along the way too, not only saving money on tyre purchases but possibly also on fuel usage & other things as well - but keeping tyres on the vehicle past their 'use by' date isn't a good thing! ;)
An Ex-Service person is someone who thought enough about their country & how great it is, how lucky we are to live here, to write a blank cheque made out to 'The People and Commonwealth of Australia' for the value of 'Up to & including my Life!'

harts
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Re: 4PSI RULE - Tyre Pressures

Unread post by harts » December 7th, 2011, 7:54 pm

thanks for the reply Peter. However, i was trying to refer to that the manufacturer gives a '5 year' period till the rubber deteriorates. Then because they have to get in the country and get stored some of our 'new' tyres are already a year if not more old! So basically the tyres will only last another 4 years no matter what you do till the rubber deteriorate.

But i agree, safety, ride, handling, and fuel economy will be perfected by using the 4psi rule. Sometimes i wish my brain ticked a bit faster :).

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Re: 4PSI RULE - Tyre Pressures

Unread post by ruffnut09 » February 19th, 2012, 12:34 pm

I have used the 4psi rule for years in trucks, buses,cars, 4wd's, trailers, motorbikes and I believe it works. With the advent of tyre monitors it is so easy to get the pressures spot on. For instance, on the trip to Cape York a caravan was towed from Melb. to Port Douglas then the Cape was done using a roof top tent. Tyre pressures towing van (cold) front 34psi rear 44psi not towing F 34 R 36 and the tyre pressure monitor has paid for itself on that trip by alerting me to a tyre losing pressure and stopping in time to fix rather than destroy a tyre.

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Re: 4PSI RULE - Tyre Pressures

Unread post by Eddy » March 2nd, 2012, 9:11 pm

Many people are losing sight of the fact that the "4 PSI rule" is intended as a simple and basic guide.
It will never be perfect for every tyre on every vehicle. nothing can be or ever will be, not even the tyre manufacturers' specs.

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Re: 4PSI RULE - Tyre Pressures

Unread post by Hillery » March 12th, 2012, 7:02 pm

Sorry for a dig up but im very interested in this. Ive got a GQ patrol ute with 35x12.5r15 radial Mickey Thompson claws on it. I tried out the 4 psi rule and after travelling about 90kays (1hour and a bit) the back has gone up roughly 3-4psi (correct pressure?) but the front tyres havnt changed pressure at all. Is this because bigger tyres take longer?

Any one else run these tyres or same size? Or anyone got a rough idea of what to run?
I wont these tyres to last :)

cheers

Boxhead 71
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Re: 4PSI RULE - Tyre Pressures

Unread post by Boxhead 71 » March 12th, 2012, 8:40 pm

So...... apparently you need to let the front tyres down? :confused: :confused: They must be too hard already so the side walls aren't flexing enough to build up any heat to raise the pressure. So ya need to let the tyres down. Yep? :thumb:

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Re: 4PSI RULE - Tyre Pressures

Unread post by Peter Aawen » May 12th, 2012, 6:00 pm

Hillery wrote:....a GQ patrol ute with 35x12.5r15 radial Mickey Thompson claws on it. ...the back has gone up roughly 3-4psi (correct pressure?) but the front tyres havnt changed pressure at all. Is this because bigger tyres take longer?

Any one else run these tyres or same size? Or anyone got a rough idea of what to run?....
Nope, larger tyres don't take any longer than that 1 hours worth of driving, altho they do tend to need less pressure (total air volume may remain the same tho) in them than a smaller volume tyre carrying the same weight over the same roads might. We run 35x12.5's on 15" & 16" rims & they tend to need about 15% LESS pressure in them to do the same job as our 33" tyres running under the same vehicles, but that is with our driving style & load carrying needs.

As for pressures, yep, as others have said it sounds like you are running close to the right pressure for the rear, but going too high to start with in the front. As a rough guide to work your way down to the correct front pressures, after you've driven for an hour reduce your front tyre pressure by approx 1/2 the difference between what they ARE and what they SHOULD have been if they went up 4psi from your cold start pressure, ie if you started on 38 & they are still only 38 after 1 hours driving instead of 42 then let them DOWN 1/2 of (42-38) or 4 divided by 2 = a 2psi reduction so drop them by 2psi down to = 36psi and revise your cold start pressure for the next time down to 36 psi instead of 38. It generally doesn't take too long to arrive at a figure that works for you, and once you are comfortable doing that for any particular surface, it shouldn't take you long to get pretty good at estimating what you'd need as your theoretical cold start pressure for any road surface & you can check it after an hour or so & revise up or down iaw the 4psi rule & that little calc, ultimately giving you the best balance of traction vs ride/longevity you can get.

And don't forget that tyre pressure is just one of the variables that you can control - if your tyres go up by more than 4psi you don't necessarily need to add more air, you could slow down instead, or maybe drop off some load?! ;)
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Re: 4PSI RULE - Tyre Pressures

Unread post by FJRider » May 14th, 2012, 11:46 am

Peter have you had a look at Adam Plates tyre pressure sheet I posted to this thread , page 3 viewtopic.php?f=7&t=130385

You must of driven the Oodnadatta Tk and other roads just like it , I would be interested in you opinion on Adams suggestions

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Re: 4PSI RULE - Tyre Pressures

Unread post by Peter Aawen » May 14th, 2012, 3:15 pm

Not only have I had a look at it, but I have been one of the many people who've contributed to Adam's knowledge on the subject & the eventual development of that sheet - and I've left him with quite a few tyres from a variety of vehicles over the years where the owners didn't get the pressures right too :D

He's collated that info on 'what pressures work' over many years of experience out there & those figures are the guidelines that result. Funnily enough, none of them are too far off what most people end up arriving at if they follow the 4psi rule; but the 4psi rule does tend to cater just a little better for the wider variations that can occur in the way people load their vehicles, drive them, the tyre sizes they run etc.

I believe the 4psi 'rule of thumb' & those guidelines that are also a 'rule of thumb' guide support each other pretty well. You can use the 4psi rule to confirm that the pressures you are running in accordance with that sheet are pretty right; and if you have different sized tyres or any other variables that might make your specific needs a little different, then using those figures as a start point & then fine tuning your pressures with the 4psi rule won't hurt at all & could well save you a tyre or excessive wear.
An Ex-Service person is someone who thought enough about their country & how great it is, how lucky we are to live here, to write a blank cheque made out to 'The People and Commonwealth of Australia' for the value of 'Up to & including my Life!'

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Re: 4PSI RULE - Tyre Pressures

Unread post by Peter Aawen » May 27th, 2012, 9:52 pm

Quite a few posts & discussion here, basically what's here covers just about all we can reasonably cover on the subject without getting too repetitive (or argumentative).

If you seriously want try it, then give it a chance to work for you & put in a little effort to get on top of it, after that first bit of effort most people don't take too long to work out how to get quite good at estimating what start pressures to use in any given situation & then generally won't need to spend too much time with a tyre pressure gauge apart from the odd check to make sure their tyres/pressures are still doing the right thing - but if you are a skeptic or just don't want to try it for yourself, then I'm sure we'll all be happy for you if don't, just don't complain about getting less than optimum traction, life, or performance from your tyres. ;)

If you want to ask questions that aren't covered in the discussion already, you can PM me & I'll see if I can help - if it's something new or something that warrants further explanation, then it might even get added to the thread. But if you only want to know what pressure you should put in whatever tyres you are running under your vehicle, don't waste your time, just use any of the methods discussed earlier in the thread & if you like, you can then use the 4psi rule to fine tune it for the particular set of conditions facing you at the time.

So with that, in response to requests & advice from the powers that be here, I'll close the thread for now. Enjoy :D
An Ex-Service person is someone who thought enough about their country & how great it is, how lucky we are to live here, to write a blank cheque made out to 'The People and Commonwealth of Australia' for the value of 'Up to & including my Life!'

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