Tire pressure is a complicated thing but don’t fall for its tricks! You’ve probably all heard that when your off road to lower your tire pressure. Well I can tell you that if your not doing it your really missing out. Let’s start with the easy part first shall we. When I drive on a standard bitumen road with our Range Rover and 235/85-16’s we usually run the front tires at 42psi and the rears at 60psi which seems to be right for our very heavy vehicle. The manufacturer states 28/41 psi but with our load and vehicle changes we’ve had to alter that. All is great until we hit those very normal dirt roads which you get a good reminder of if you run those higher road pressures. We then pull over and drop the fronts to around 30 and the rears to 40. Instantly you now have a better ride and could save your tires as well, but will talk about that in a minute. Now those tire pressures are just a starting point as the worse the road, the lower and slower you go, but I dont think I have ever been lower than 25 and 30 respectively on corrugated roads. You see tires are also part of your suspension system, the less pressure the more flex and more compliant the tire is to irregularities, you really want that balance between tire compliance and safety or pressure vs speed is how I look at it. I had a small and very light rock crawling trail rig that sported 35 inch tires and I would regularly drop the pressure to 5 psi to increase traction and with that vehicle it looked like a normal tire pressure!
When you have a hard bitumen road pressure the contact point is smaller and more direct, when you hit those fist size rocks the pressure is concentrated on a smaller area which means the tire takes a much harder hit and of course it then transfers through to the vehicle. When the tire has a lower pressure it conforms more and soaks up the punishment a tad bit better which then helps the tire, shocks, vehicle and your back! The last tire related happening on my books is a large metal rod that buried itself in the rear tire. Amazingly it went into the tire and was stopped, and presumably bent by the tire belts. No puncture that day but I am pretty sure that if the tire would have been at 60 psi it would have gone right through and possibly destroyed the tire because of the more rigid tire. [picture]
On these types of roads you don’t want to go to low as the tire also provides stability and like we talked about, the lower you go the less side stability you have. I’ve seen vehicles roll due to speed and a directional change, just have a look on YouTube to enjoy others mistakes. Many of use have been that “rally driver” on occasion but when you hit that corner at 60mph and your tires only have 25 psi there’s a very good chance the last thing you remember is seeing the front drop then you were in a tumble dryer!
This happens more than you would believe in sand, sand tends to engulf the tire and pull it right off the bead, but sand is soft so your rig might not be to damaged! Now let’s talk about sand, it still stumps me on occasion as it is ever changing. My normal start pressure is 25 psi all the way round and that usually is all good. If it’s very soft I’ll drop it to 18/20 and can run all day. [picture]
The weird thing about sand is that the same area one month can be a nice easy path but wait till a hot dry day and that same path can be a very difficult to get across. Sometime you can just keep on the gas and paddle through a soft section and other times the slightest wheel spin sends you to bog city! Like everything the more you do it the better you are at judging the right recipe for success.
The final piece is whatever you do take the time to re-inflate your tires back to the pressure for the road condition change. You see tires have layers to them and those layer believe it or not rub together and create heat. When you return to bitumen and your tires are less than half the pressure there supposed to be they can literally explode in just a few miles when traveling at highway speeds from the high temperatures that will be generated and a catastrophic end to an epic trip is not what you want. Each vehicle is different and it takes time and bit of observation to get your vehicle pressures right but a good starting point is the manufacturers recommendation that’s listed. Beyond all else have an epic journey and be safe!