Tyre pressure for black top: who to believe?

The manufacturers recommendation.

As long as the tyres are the size and specification stated on the vehicles tyre placcard, then go with the manufacturers pressure recommendation every time, if you have different size/type tyres to what is on the placcard then talk to the tyre manufacturers technical department which can usually be found on the webiste, and a bit ot trial and error using the 4psi rule.

I would disagree with that.

The Vehicle Manuafacturer isn't interested in tyre life. That is not their concern. The Tyre Manufacturer would be better for advice (and that DOESN'T mean , tyre shops/fitters).

26psi , would be good for vehicle handling as it allows the tyre to move , heat up , and get maximum grip, however , it also SEVERALLY effects the life of the tyre.

Its all about compromise.

A lot of us use what they call the 4 psi or Pirelli Rule.

The tyre should increase by a max of 4 psi between cold , and hot after a decent run of approx 15 mins.

In my case , in both my 4wds , between 36 and 38 psi gives that end result.

My tyres (BFG AT's) are all around 80,000 k's with a bit of life left in them.

I always go at least 10 psi above the manufacturer recommendation. The reasons are:
1. You use less fuel
2. Your tyres last longer (less wear)
3. Can't remember the third one...

If they are bridgestone 693's 30psi is plenty.
On a Patrol I use 30 front and 28 back. And
after travelling an hour down the hwy, they only go up about 1 or 2 psi.
So the 4psi rule says they could go down about 27.
Anyway I know 693 are not a true light truck construction tyre,
But I have had 40K of trouble free km on them. I don't trust them much on the gravel roads around hear anymore. But if I just used them on the hwy now I
might get another 10K out of them.

None of them. They are only a guide.

The Manufacturer recommendation is a good starting point, but usually rated too low for good tyre wear or optimum performance. This pressure is optimised to give the "best ride" comfort wise on the blacktop and you could go up at least 4-6psi.

You are better off performing your own test using the 4psi rule.
Then YOU can tell the service people what YOU require.

Over a period of time, an under-inflated tyre will show abnormal wear on the outside edges of the tyre. An overinflated tyre will show the wear in the centre area of the tread as the tyre will tend to "balloon" out. This is probably the worst for grip as only the centre portion of the tyre will be touching the road surface.

Mate, if your tyres measured 40psi after they had cooled down they would have been running close to 44psi when hot. (Assuming the tyre gauge is accurate).
This sounds way too high.

Sly,

You have already received lots of good advice, above, but here's my 2 cents worth anyway:

1. Vehicle manufacturers will always recommend and placard tyre pressures at the lower end of the tyre manufacturer's recommended pressure range. Lower pressures allow greater sidewall flexibility, which in turn provides a softer ride and greater passenger comfort. Tyre wear doesn't really enter into a vehicle manufacturer's criteria when placarding tyre pressures.

2. On several occasions I have heard stories related by reputable race and rally drivers that increasing tyre pressure increases tyre performance and grip. In one such story, tyre pressures on a Commodore/Falcon-type sedan was increased successively in 5 psi increments, and the car then timed on a race circuit. Lap times continued to be reduced with each successive increase in tyre pressure, until something silly like 60psi was in each tyre. (These were normal road tyre, not racing tyres.) This suggests that tyre performance is enhanced by increasing the pressure. (Don't know how this relates to 4WD tyre performance).

3. Under-inflated tyres will suffer increased wear at the edges of the tread, thereby decreasing tyre life. Over-inflated tyres suffer increased wear at the middle of the tread, also reducing tyre life.

4. There is quite a large range of pressures over which a tyre will operate without compromising on performance (grip) or safety. I commonly run my tyres at 5-10psi above the vehicle manufacturer's placarded tyre pressures and am very happy with both the tyre performance and the tyre life that I achieve.

Hope this helps.

All good advice but if you were in court and it meant going to goal, i know who's recomendation i would quote.

And it's comfort and handling for these pressures.

Ring Cooper tyres and ask them, i did when getting a warrenty replacement of their tyres, one of their question was what pressure was i running.

Baz.

Find a wheel alignment dude that really knows his stuff and he can show you how to read the wear on a tyre to determine if the pressure is too low or not it is quite simple once shown. The tyre when underinflated for the driving condition rolls too far on to the edge of the tyre and shows in certain wear characteristics easily identified. My guess is that this is why the tyre service has looked at your tyres and said you need more pressue. I run 40 on the highway on just about all the brands and drop immediately i get on to dirt down to 24 to 30 and as far as 18 to 22 on rough 12 to 16 on sand all these being set at the start as the sand pressures after an hour or so will be considerably higher.
Everyone has their own preference but I never had less than 110000 out of any brand and never shredded any tyre even on ther cordillo to Birdsville so I must be reasonably close. ( reduced presures should not be run too far over 90kph for reliability)

26PSI, Hell I would not feel comfortable driving on the road with that pressure.
My tires sit on around 45-50PSI (cold inflation) temp when on the black stuff Cooper stamp say’s 50Psi cold temp.

Stay close to the tyre manufactures Pressure stamp and you will be fine, yes the ride will be harsher but tyres will hold the road much better and fuel economy will be better to.

With a max Cold inflation temp of 36 I would be inclined to run them at around the 32PSI or higher mark.

Having the tyres “sponge” around on the road will not give you good grip or handling it will make the car ride smoother and that is it. IMO

Everyone goes on about pressure. How many have EVER had thier gauges checked on a calibrated gauge for accuracy. Tyre gauges can very heaps, both low and high readings. I run 26 to 28 psi for normal running, (Pathfinder,jackaroo,triton and prado) up to 45 psi in triton`s fully loaded. With 18 foot poptop van still only run 28psi rear. All my trips north only normaly run 26-28 psi and drive to road conditions. Have our shop gauges checked twice year on calibrated gauge.
Cheers
Charlie

Thanks for all the info guys. Lots of good advise. I'll try the 4psi rule and double check the pressure using my guauge and several others (friends and petrol station) to see if it's accurate.
Sly.

Alot depends on the size of the tyre.As being a mechanic I monitor my customers tyre wear in relation to pressures.I normally put 36psi inthe front and 32psi in the rear for standard passanger cars.My own commodore with 235/45 17 tyres(low profile)I run 42psi front and 38psi rear and they still show signs of under inflation.I have a customer with a 96 80series Cruiser GXL on standard tyers,serviced every 5000km for 210000,tyre pressures,front-38psi,rear-34psi,perfect tyre wear.The thing is to find the right pressure to suit your car and driving style.A word of warning,I have seen cars that have just had tyres fitted at big name tyre shops and the pressures have been all over the place.All the best Peter.