tyre pressure

The tyre placard on my 110 has pressures varying from 35/35 to 60/65 depending on load and speed. Notably, these figures are the adjusted ones for Australia, and are about 5psi above the UK figures - see below. I usually run 35/35 empty and 40/50 at the maximum load I normally run.

Tyre pressures are always a compromise. A minimum is set by the pressure that will prevent a dangerous pressure rise (and this depends on ambient temperature and speed as well as load), but other factors may require a higher pressure.

From the tyre manufacturer's point of view, generally the higher the better, as even a small temperature rise will shorten tyre life, especially in areas with high ambient temperatures.

From the car manufacturer's point of view, other factors come in. The lower the pressure the better from the comfort point of view, but higher pressures will generally give better handling, and in particular a car's inherent handling characteristics may require an apparently strange difference front to rear. So the tyre placard figures (which have legal force) are the manufacturer's compromise to give a ride that will not upset passengers too much, and handling that will neither upset drivers nor lead to liability claims.

(Pressure affects both the faithfulness with which the tread follows the direction the wheel is pointing despite side loads, and the amount of and shape of the contact between the tread and the road, although this is less affected with radials than with crossplies)

While the minimum set by temperature rise mentioned above will vary quite a lot between different tyres, depending mainly on construction and rubber composition, the ride and handling is less affected by these factors, and even less by changes in tyre size.

John

The opening statement of this thread is a contradiction.

Quote:

---

Recently, I was told by a mechanic at a tyre franchise

---

I have never seen a mechanic at a tyre franchise. I have only ever seen high school dropouts who know nothing about anything. ( nothing about nothing sounds better but I am concious about my grammar these days. I do not want to be criticised)
I wonder if he is the same one who sets the rattle gun at 300ft lbs?
Seriously I would take NO notice of what someone at a tyre franchise says. I would take notice of a tyre placard , as the carmaker has tested the pressures and knows the weight distribution of his car. Alter a bit for all addons. Maybe I would take notice of an engineer at a tyre MANUFACTURER , but not an importer.
Regards Philip A

Quote:

---

Originally Posted by PhilipA

<snip>
Maybe I would take notice of an engineer at a tyre MANUFACTURER , but not an importer.
Regards Philip A

---

I've actually worked with them, and they do what we do, try a pressure and see how it goes :p

I just walked out and had a look at the tyre placard, and it suggests 44/65 fr/rr psi for on and off road work, all load conditions......Nice how it's different to the handbook, I wonder how many people realise the tyre placard takes precedence over anything else ?

Anyway, 65 psi in the back of an unladen 130 is still ridiculous, 65 psi with one tonne in the back is suitable.

Quote:

---

Originally Posted by PAT303

The idea that low pressure causes the tyre to bend around rocks etc is a load of crap.

---

:lol2:

Well I run 40's all round. Find it suits the Landie. Don't see any necessity to put more in the rear, as she's unloaded most of the time.

Very interesting range of comments here. Bob Jane T marts put my tyres on and gave figures of 38 for front and rear on D1. I asked about how they came up with these figures and was told that was the tyre manufacturers advice for that tyre on my vehicle. This pressure is higher than placard which is probably because the lower pressure would enhance ride and grip quality on their vehicles. The majority of people wouldn"t even notice the difference in fuel economy or tyre life unless someone told them they could get better mileage with slightly higher pressures. Off road is very much a compromise lower pressures bigger footprint better traction and less puncture chance in tread area due to the fact it flexes around objects more. The sidewall however is more vulnerable at lower pressures due to this extra flex. If you are travelling in a remote area if you ask the ranger what pressures they run in those areas you can use this as guide. (Just compensate for vehicle and load).

The "4 psi rule" has been around a while although I notice that the NRMA says for large 4wd tyres that it should probably be more like 6 psi:

Whilst this quote from the NRMA is for trailers and caravans the same principle applies for other vehicles.

Quote:

---

Tyre pressures - do-it-yourself check





It is impossible to list the correct pressures for every caravan, due to variation in size, load, etc. This easy check will help you find the best pressure for your caravan tyres.

• First inflate the tyres to the pressure recommended by the manufacturer of the trailer or the tyre you are using. Secondly, tow your trailer for a distance of 100 km, preferably on a highway.
• Recheck the tyre pressures immediately after pulling over and compare them with the pressures you had at the start of your run. If the pressures are right, the hot readings should be 4 psi (28 kPa) higher than the cold readings.
• If there is a greater than 4psi (28 kPa) difference between these pressures, the tyre temperature is too high and the pressure needs to be increased. If there is less than 4 psi (28 kPa) difference, the pressure needs to be lowered.
• Large 4WD tyres will have a differential of 6 psi (42 kPa).
• Be sure to use the same accurate gauge for both readings.

---

I've used it to get a feel for what pressures to use for higher speed and laden trips when I changed over to a different tyre make.

Quote:

---

Originally Posted by dhard

Very interesting range of comments here. Bob Jane T marts put my tyres on and gave figures of 38 for front and rear on D1. I asked about how they came up with these figures and was told that was the tyre manufacturers advice for that tyre on my vehicle. This pressure is higher than placard which is probably because the lower pressure would enhance ride and grip quality on their vehicles. The majority of people wouldn"t even notice the difference in fuel economy or tyre life unless someone told them they could get better mileage with slightly higher pressures. Off road is very much a compromise lower pressures bigger footprint better traction and less puncture chance in tread area due to the fact it flexes around objects more. The sidewall however is more vulnerable at lower pressures due to this extra flex. If you are travelling in a remote area if you ask the ranger what pressures they run in those areas you can use this as guide. (Just compensate for vehicle and load).

---

This is what Pirelli "says" about tyre inflation pressures and tyre life:

https://www.aulro.com/afvb/images/im...2008/06/29.jpg

Thanks JDNSW & Iota