Another Tyre Pressure Query

dave48 · Senior Member

Another Tyre Pressure Query

nswoutback · Member

The steps for highway travel;-

1) Establish tyre load
2) Establish tyre size / full specification (read all the critical numbers and words stamped on the tyre).
3) Establish optimum tyre inflation pressure from the best reference, the load inflation charts.

If you propose to reduce tyre inflation pressure for slower travel speeds, the steps are;-

4) Determine the proposed maximum speed and adhere to this maximum speed.
5) Apply the tyre inflation pressure factor based on the chosen speed multiplied by the optimum tyre inflation pressure.

Peter_n_Margaret · Guru

Keep a close watch on tyre temperatures.
I do this by measuring the temperature with an infra red thermometer every 15 minutes or so and ensuring that it does not exceed 65C. If it starts to get close, SLOW DOWN.
It is excessive temperature that will destroy the tyres.

Cheers,
Peter

dave48 · Senior Member

Thanks guys. Thanks Peter I'm always wary of the temperature. Andrew I'm not quite sure what you mean by 5) Apply the tyre inflation pressure factor based on the chosen speed multiplied by the optimum tyre inflation pressure. Would you be kind enough to explain. Dave

nswoutback · Member

If you do not exceed say 70km/hr, you might drop the pressure to say 80% of highway pressure.

If you do not exceed say 50km/hr, you might drop the pressure to say 67% of highway pressure.

Aus-Kiwi · Guru

Explorer pressures 90lb is recommended . Up north I dropped pressures to 70lb . It took a lot of harshness, body harmonics out . Tyre was warm to touch with bare hands . Was tempted to try lower pressures ? But thought leave it ! 19.5 /70 series 225 Michelinâs . Theory is I am WELL under max weight . 70 Lb on duel tyres did not effect driving !

dave48 · Senior Member

Thanks guys I really appreciate it. Will now do some testing but Know roughly what pressures are involved. Great help. Cheers Dave

oldred83 · Newbie

Hello Andrew..

I have read with interest your thread on Tyre Pressure.

Cooper tyres recommend the following...

"There is no universal right pressure for all tyres. The proper inflation level is dependant on many factors such as what tyres you have, type of vehicle, amount of load, how the vehicle is being driven and the condition of the road to name a few. The important thing to remember is, as load increases, you will need to increase pressure but never exceed the maximum pressure stamped on the sidewall of the tyre. For harsher road surfaces, a lower pressure with lower speed may be needed to avoid tyre damage".

"As a general rule, the following can be used - for road use only: For passenger tyres, inflate your cold tyres to the recommended tyre pressure on your vehicles tyre placard*. Then to determine if you have the correct pressure for a given load, note the cold pressure reading. Drive for at least 20-30 minutes to ensure they have reached operating temperature and then check again. Ideally, they should be about 4psi above the cold pressure. If the pressure is more than 4psi above the cold pressure, you should add more air. That is because there is too much friction, which builds up more heat than desirable. Conversely, if they are less than 4psi above cold pressure, the cold pressure is too high. Adjust your pressures accordingly.

For Light Truck and 4x4 tyres, use 6psi as a guide, but rough and corrugated roads cause more flexing and your tyres may rise more than 4 or 6psi. In which case applying this rule is not recommended".

However, the principle can still be used. The lower the tyre pressure, the slower one should drive. Pick a speed which suits you, your rig and your other half. Lower the tyre pressures gradually. Say 5 psi at a time. Monitor your tyre pressures, record the readings. This process will take a while, but you will eventually determine the optimum pressure for the different grades of corrugated road for the speed you are comfortable at. Remember, you will not find the exact pressure, as ther are too many variants in road surfaces, temperature

oldred83 · Newbie

Hello Andrew..

I have read with interest your thread on Tyre Pressure.

Cooper tyres recommend the following...

"There is no universal right pressure for all tyres. The proper inflation level is dependant on many factors such as what tyres you have, type of vehicle, amount of load, how the vehicle is being driven and the condition of the road to name a few. The important thing to remember is, as load increases, you will need to increase pressure but never exceed the maximum pressure stamped on the sidewall of the tyre. For harsher road surfaces, a lower pressure with lower speed may be needed to avoid tyre damage".

"As a general rule, the following can be used - for road use only: For passenger tyres, inflate your cold tyres to the recommended tyre pressure on your vehicles tyre placard*. Then to determine if you have the correct pressure for a given load, note the cold pressure reading. Drive for at least 20-30 minutes to ensure they have reached operating temperature and then check again. Ideally, they should be about 4psi above the cold pressure. If the pressure is more than 4psi above the cold pressure, you should add more air. That is because there is too much friction, which builds up more heat than desirable. Conversely, if they are less than 4psi above cold pressure, the cold pressure is too high. Adjust your pressures accordingly.

For Light Truck and 4x4 tyres, use 6psi as a guide, but rough and corrugated roads cause more flexing and your tyres may rise more than 4 or 6psi. In which case applying this rule is not recommended".

However, the principle can still be used. The lower the tyre pressure, the slower one should drive. Pick a speed which suits you, your rig and your other half. Lower the tyre pressures gradually. Say 5 psi at a time. Monitor your tyre pressures, record the readings. This process will take a while, but you will eventually determine the optimum pressure for the different grades of corrugated road for the speed you are comfortable at. Remember, you will not find the exact pressure, as there are too many variants in road surfaces, road temperatures, loads, driving conditions etc etc, but a bit of time experimenting with pressures and feeling the temperatures of the tyres will eventually pay off.

On another note, it is my experience the notion of rising above the corrugations by driving fast over them, especially severe corrugations is a sure fired way to damage your rig, damage contents, increase the risk of losing control and frustrating tempers. I know it can be very frustrating, but the bigger the corrugations the slower you need to travel.

Kind Regards

Oldred83

StewG · Senior Member

I also was unsure about tyre pressures for my new rig. After extensive Googling and use of other forums I selected nominal pressures for the six tyres involved and bought a Tyre Pressure Monitoring System to be able to monitor pressure and temperature constantly while on the move. After some teething problems with the TPMS; the caravan tyres would not report back to the display until a transponder was installed at the back of the car - now installed permanently on the caravan. Pressures, of course are highly dependent on temperature and ambient temperatures vary widely throughout Oz. So it is hard to give an exact pressure, but if you have a good compressor and accurate gauge, it is easy enough to experiment until you're happy with the results that give you economy, comfort, grip, sidewall protection and even wear of tyres (not necessarily all at the same time). biggrin