Hey Simon, what tire pressures are you running on the 16"s?

They look quite low from the pics you took, and it might help handling a bit to bump them up to ~65psi or so.

 

Hi Adrian,

thanks for your observation.

The Costco fitter set them to 43psi. It felt really floaty on the short drive home, where I took the photos.

For the highway trip I increased the pressure to 60psi all round.

I'll give 65psi a try. Any thoughts on running the front tyre pressure higher than the rear for unladen use?

 

Hi Simon,

Hope Adrian doesn't mind me throwing in 2c worth, split pressures front to rear is no issue as it is the load on the tyre that determines the optimum pressure.

If you purge out the straight nitrogen from the tyres you can then use the 4 psi rule to find the correct pressure for your load. From cold pressure to hot after driving you should have a 4 psi higher reading, less than that the starting (cold) pressure is too high, more than that the starting pressure is too low. Obviously too low is more of an issue as it creates heat in the carcass which is what causes delamination and blowout. Too high will just make it ride skatey and harsh and wear out the centre section of the tread.

 

Thanks for that info Brad. I'll start monitoring the tyre pressures more closely.

The BFG TA's sidewall rates the max load capacity of the tyre at 80psi, so I'm running well under that.

I think I'll start looking for an on-board air system!

 

FWIW, I typically run 65-70psi in the fronts all the time, and run 50psi in the back when empty, and 80 when laden.

 

I did a lot of playing around with pressures on the trip around Australia. I'm finding 62 cold (raises to 65 hot) in the front and 58 cold in the rear (raises to roughly 63 when hot) gives the best balance between a rough ride and performance (term used loosely of course in a truck). I think I could get away with a little less air in the rear, maybe, and that might help the ride a little more.

When I was carrying the camper I was at 75 cold and 80 hot (all four)

Cheers, Mal.

 

I tried with a trip from the NSW South Coast to Canberra. Started with 65psi in the fronts, 60psi in the rears - 3 up, 2 dogs, back full of luggage and DIY tools, probably a couple of hundred kgs at the most.
As soon as I stopped the truck I checked again, so tyre were hot, 72 in the front and 67 rear.
I expect some of the +7 psi increase was due to the 600m elevation gain.

 

According to this handy chart you will get 1 psi drop in atmospheric pressure for 610 meters.

Air Pressure and Altitude above Sea Level

 

A cool morning and a hot day (hot road) can push the temps (and pressure) up more than you expect when you check it later. I had to adjust cold temp pressure when I was in the NT (as pressure raised too much) and then when I was in the south of WA (the cool days didn't allow the pressure to get high enough).

I've been trying to get 65 PSI, unloaded, when the tyres are hot (without starting at a pressure that's too low in the morning).

EDIT: Oh I forgot to say, the speed you're travelling plays a big part too. Get on the freeway at 110+ and they'll heat up more than driving around at 60k's.

 

Interesting stuff. So I got one extra PSI in my tyres due to the decreased air pressure due to altitude gain, and an extra 6psi due to temps. I started the day in the cool, was driving at 100kmh on the black top after 60km of dirt between Moruya & Araluen.
The road was hot, in one place near Braidwood, the tar on the road was melting.

If I understand it properly, according to the rule of 4psi, I probably needed 67 in the fronts and 62 in the rears at the start of my journey.

Also Mal, thanks for your thoughts and observations. I'm going to start monitoring my tyre pressures every journey now.

ATM I'm not sure whether to get a dedicated on board air system, i.e. pump, tank, manifold, etc, etc, or just one of those 'allegedl' Heavy Duty 4x4 portable units for about a quarter of the cost

 

I installed Tyredog for the truck and trailer. It's a good system, fast and pretty accurate too. I carried the biggest portable air compressor I could get (actually I had two, one with a built in jumper battery just in case)

 

Sounds good Simon, I wouldn't go for the full on board air system, or belt driven compressor, a decent 12 volt unit with hoses etc. in a toolbox case will do everything you need short of running serious air tools.

IMHO the best units are the opposite lock "blue tongue" or if you can afford it, the " twin tongue" they are made by Thomas pumps in the US. Next best are the ARB compressors.

If you just want cheap and Chinese, I think the best are the Tigers 11 or Roo units.

 

Depends on what you want to do to a certain extent.

If you are just adjusting pressures a bit every now and then, and you want something so you can patch/inflate on the side of the road, a portable unit is fine. Make sure you get one that is 100% duty cycle however. I find Viair makes good ones: VIAIR Corporation - Portable Compressors

If you don't mind doing a bit of fab work, you can mount a Sanden air conditioning compressor in the spot for the second alternator that runs off the fan/FEAD belt, takes quite a bit of work, but they will be far and away the most powerful option. This is a good read: Grungles Homepage

I am putting an OBA setup on my truck now, so I can adjust the airbags I am fitting on the rear suspension and I want the ability to run an impact wrench, so need something that will put out quite a bit of air. I am using this: VIAIR Corporation - 444C Dual Value Pack (P/N 44432). I got 2 for capacity, and for redundancy, because one will always fail when you need it most.
Both compressors mounted behind the back seats to keep them out of the dust, and will have a 10l tank mounted on the outside of the chassis rail on the left side of the truck. They will be wired off one of my upfitter switches, with a 150psi air pressure switch on the tank as well. (i.e. air pressure has to be below 150psi, and switch has to be "on" for them to turn on...)

Most air tanks act as "manifolds" as they usually have multiple outlets. Truck wreckers are good places to get air tanks, as they all use multiple tanks for their air brakes, and they usually have mounting brackets built in already to attach to the chassis.

 

Hi Adrian,

Yes truck air tanks are great, especially the stainless steel ones.

Are you sure on the 150 psi switch? Max allowed for shop air here is 100 psi. Plus i note those compressors are only continuous rated up to 100 psi.

 

I use a York AC compressor. Used for compressed air at 150 psi it is way under design capacity. There are a lot of brackets out there made to fit them, mostly older cars and trucks, this would be a belt drive system. Choose your own tanks etc. Amazingly cheap and reliable. You may have to do some fab work.