Thread: 245 70 A/T Pressures

For 'normal' highway/road work running the placarded tyre pressures will do you right.

For our D2a bought new in 2004 the original Michelin XPC's lasted 90,000 Km including a fair bit of off road central Australian touring where the pressures were often dropped to suit the terrain ie. Simpson Desert crossing. Replacement tyres were Kumho somethings (highway pattern) which lasted approx. 80,000 Km and were changed with some tread left as they had gone hard and no longer gave a comfortable ride. The replacements were another set of Michelins, this time Latitude Tour HP's which are now firmly affixed to my replacement 2002 D2 and have about 2mm of tread left above the wear indicators. I reckon these have done about 70-80,000 Km of mainly highway use. Tyre wear was/is even for all these tyres and they weren't rotated as per the manufacturers instructions.

The placarded pressures for the D2 is 28/38 psi for normal operation and I assume it was pretty much the same for the D2a though I can't remember specifically, but I do know they were run at the placarded pressures.

The tyres were/are 255/65 R16's on factory 8" rims.

I can't see the point in running higher pressures when the factory figures give such good results in both handling and longevity. The only benefit I could see (of running higher pressures) is that the centre of the tyre would wear down quicker reducing the life/mileage of the tyres thus giving the tyre retailers more sales

Deano

Originally Posted by Pippin

Thank you for your wise words V8Ian. Do you think after nearly fifteen years of D2 ownership I don't know the prescribed pressures? The D2 I have just bought and replaced the engine has the AT's and my question is a fair one.
Nick

Using the 4psi rule I have found placarded pressures to be spot on in my 245/70 bf Goodrich all terrains in light truck construction. 28psi in the front and adjust the rear according to the load as per the placard.

Thank you for all the replies. I read a good quote that if you ask this question you will get many different answers. I will be sticking to the recommended basic 28F 38R cold and adjusting accordingly if greater than a 4psi hot increase by adding 2psi and if less than 4psi increase reducing pressure by 2psi until there is a constant 4psi between cold and hot. But first I have to make sure I have an accurate gauge.
Nick

The placard assumes light weight in the front end. I added 4psi to the placard dor the dront for the steel bar, recovery points etc.

I still wonder if light trucks (for their longevity) need or do better with higher pressures to avoid scolloping.

Cheers

Originally Posted by ozscott

The placard assumes light weight in the front end. I added 4psi to the placard dor the dront for the steel bar, recovery points etc.

I still wonder if light trucks (for their longevity) need or do better with higher pressures to avoid scolloping.

Cheers

The reason I asked the question was there appeared to be greater wear in the centre, particularly on the fronts.
Nick

Originally Posted by Pippin

The reason I asked the question was there appeared to be greater wear in the centre, particularly on the fronts.

Originally Posted by Pippin

Nick

My simple brain would indicate that means pressure is too high? I'm sure it's not that simple though.

Originally Posted by Pippin

Thank you for all the replies. I read a good quote that if you ask this question you will get many different answers. I will be sticking to the recommended basic 28F 38R cold and adjusting accordingly if greater than a 4psi hot increase by adding 2psi and if less than 4psi increase reducing pressure by 2psi until there is a constant 4psi between cold and hot. But first I have to make sure I have an accurate gauge.
Nick

Good to see other people using the 4psi method - an accurate gauge is essential. I have heard good things about the Intercomp gauges from the states (INTERCOMP 0-60 psi Deluxe Tire Pressure Gauge P/N 360064 | eBay). I'm asking for one for my Christmas pressie as they retail around $100.

I think the essential thing with a good tyre gauge is that it is 1) properly calibrated (which means no cheapies unfortunately) and 2) looked after appropriately. You cant drop them or they're buggered is the best explanation.

I generally say to customers for normal running around on the road start at 40psi
If you run constant heavy loads you may need to tweak this up to 45, most AT radial tyres have a max of 50psi when under max load.
Then really you should check pressures on a regular basis, at least once a month.
Adjust pressures according to wear.
You will find the old 30psi will be a bit low for most modern radial tyres.

Regards
Daz

Originally Posted by Pippin

The reason I asked the question was there appeared to be greater wear in the centre, particularly on the fronts.
Nick

if the center is wearing it will most likely be too high of Tyre pressure, but it can happen from extremely low pressure as the center will flex out from centrifugal force
if you want better fuel economy run max pressure on that's on the Tyre
if you just do general driving around anywhere between 30-36psi will be fine

ozscott

The placard assumes light weight in the front end. I added 4psi to the placard dor the dront for the steel bar, recovery points etc.

I still wonder if light trucks (for their longevity) need or do better with higher pressures to avoid scolloping.

Cheers

scalloping is generally caused by ether ball joints and tie rod ends being worn or over pressure basically allowing tyre to jump, with LT tyres due to the sidewalls being much stiffer then originally specified a shock that is calibrated for those original tyres wont be able to control wheel and stop it from skipping
so you might find you need to run 2-4 maybe even 6 psi less pressure to get similar sidewall flex so the shock can control the suspension again.

Load & Inflation Tables | Michelin Truck
i have attached a link to chart that shows tyre pressure to maximum load if you have a 10ply tyre on then you should roughly at 35psi have 1600kg on that axle or 800kg per wheel, now if you only have 500kg on that wheel the tyre is not going to absorb the bumps and will jump and skip which will lead to scalloping.

reason i know this is we had really bad issues with scalloping on trucks and esp dog trailer tyres and tried different shocks and making sure all the play in the suspension was gone then i went and found that chart listed and dropped the truck/trailer tyres from the tyre service 100-110psi down to 80 for all the dual and 90 for the steer and we stopped having a lot of scalloping issues with the tyres unless they do a lot km's empty, we also stopped having shocks fail as much as well and less wheel bearing adjustments.