Torque N' 4WD. Part8
08 February 2008
As a follow-up to my last article on purchasing the right tyres for your 4WD I have chosen the topic of tyre pressures. This subject causes just about as many arguments as which vehicle to buy. I have read many stories from experts in the tyre game and they all seem to have different ideas. I like the 4 lb. theory. ‘Please explain?’ I hear you ask.
As I suggested with the purchase of the correct tyres compromise is always present. What we are looking for is the best performance (tyre life), drivability and comfort you can get from your chosen tyres. Comfort might sound a bit strange when discussing tyres but we are not only talking about looking after the occupants of the vehicle but also the vehicle itself. Because your vehicle has varying loads to carry your tyre pressures need to be different.
How do you decide what tyre pressure to use? An example I can give is as follows. On a recent trip to Queensland with my vehicle towing a camper trailer and loaded to the gunwales, as is usual on most camping trips, I had an educated guess as to what pressure I would require. My choice was 40 psi for the rear tyres and 36 psi for the front. After traveling for about 100 km I checked the pressures and found that they had gone up by my mythical 4 psi. The build up of pressure is due to the tyre flexing. The tyre having the ability to flex creates a more comfortable ride in the vehicle. Had the pressure increased by a greater amount this would indicate that the tyres were flexing too much and creating a greater amount of heat and forcing up the pressure. Conversely had the tyre pressure not changed this would have shown that my original starting pressure was too high.
When it came to choosing the tyre pressures for the trailer a much lower pressure was required because the trailer is carrying a lot less weight. I usually run less than 20 psi on the trailer, which allows the tyres to flex and act as part of the suspension.
Now I can’t tell you what pressure you will need with your particular vehicle and load - this is something that you will have to work out by trial and error. A good starting point would be to consult your reputable tyre dealer and also the tyre placard affixed to your 4wd. By using this theory and the information you have gathered you will be able to decide on a tyre pressure suitable for your vehicle and the load it has to carry.
The system I have described here is perfect for traveling longer distances on the bitumen between 4wdriving. Once you leave the black top the scenario changes, as there are other things to consider. In future articles we will talk about the tyre pressures required for driving off road. In the meantime find yourself a good tyre pressure gauge because if you intend to be come a conscientious 4wdriver you will certainly find plenty of use for it.
Article written by:
Don Martin
former DTU Mount Gambier and Districts 4wd Club.