Tyre Pressure and 4WD Vehicles

I have been traveling the Outback of Australia since I learned to drive in an XL Falcon Ute, 3 speed on the column, at the age of 8; that was in 1963. Great motor car. Then we got a 179 EH Ute, you know with the 179 flag in the middle of the tail gate – that could that do circle work really well.  I’m still here ‘caus I didn’t get caught, by my father, the cops were 300km away.

When I got my licence, it was a strange thing to drive on the fancy ‘black stuff’, no rear end movement,  excess noise from the road or pot holes to watch for, but the bloody traffic…… other people, that’s why I’m still in the bush, well almost.

 “How much tyre pressure should I have?” The age old question. So long as there is air in there may be sufficient, but add a little bit of weight, speed the quest for fuel consumption, and tyre life, not to mention safety. How long is a piece of string??

 Well the vehicle and tyre manufacturer have done a whole heap of testing to make sure the tyre is going to stand the rigors of the driver. That may be OK for the blacktop, but in the bush it’s a different story. When I talk about bush I mean anything but sealed roads.

 It can be a dirt road with corrugations, bush tracks that have never been graded, climbing sand dunes in our deserts and beaches, anywhere, where the road isrelatively slow, from 80km max down to low range first and second gear.

 No matter what this situation you may need to vary tyre pressure to get through. So how much?

 OK, let’s look at what the vehicle manufacturer suggests for a specific vehicle? A Prado with 265/70 R 17 tyres on it. 29psi all round, great. Now let’s measure the tyre tread length on the ground at the front first. See the photos.

 Weight does not much changes from empty to fully loaded on the front axle, so using this as a reference point, with the tyre placard as a guide, is a good place to start. Measure the length before you start packing, then if you are not overloaded, you should be to get the same length at the back as the front.

So here we go.

-  180 - 200mm           tread length is good for most roads, inc the sealed

- 220 - 250mm             corrugated dirt road

- 300mm                     sand dunes, including the trailer.

- 400mm               about 7 or 8 psi,  when you are really in ‘it’ 

These measurements can change from car to car and tyre to tyre, you might need to do your homework first.

A fully loaded 100 series Cruiser including trailer on a Hay River Simpson Desert Trip; this is what we ended up with.

14psi (300mm) front,

22psi    “       Rear

9psi      “       Trailer, the rest is history, not a problem after that.

 Don’t forget:-

- Tyres can get hot during the day so if the temp is going up both in the sand and tyres you may need to let them down a little more at lunch time, then you need to re inflate in the am next day back to the 300mm. Slow down if they get too hot.

 

- Hot sand is more difficult, it may be necessary to halt if the temp gets too warm.

 

- To re inflate after your on hard again is a must, so one hand pump each or a good compressor, not the plastic rubbish either. ( I always take a back up pump)

 

- Be careful when turning, not to turn too fast, you could roll the tyre off the rim.

Tubeless tyres are preferred over tubed tyres.

Clare Fleming