Tyre pressure (again but different)

Submitted: Wednesday, Jun 02, 2010 at 08:06
ThreadID: 78982 Views:3536 Replies:8 FollowUps:7
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Hello all,
Why is it that the tyre pressure sticker on my car clearly states 31 psi and when I go to a mechanic or service of any description they insist on pumping them up to 38-40 psi? It doesn't matter where I take it the same thing happens and I have to go to the trouble of letting them down again. If I tell them not to do it they imply I am an idiot and don't know about such complicated things as numbers.
I don't like the ride on tyres inflated that far above recommended. It rattles the car to bits. When I was younger we never had the tyres up that far, is it the latest fashion and why are they taking no notice of the sticker?
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Reply By: Ozhumvee - Wednesday, Jun 02, 2010 at 08:26

Wednesday, Jun 02, 2010 at 08:26
Manufacturers advise of a tyre pressure to maximise the ride comfort of the vehicle.
Tyre manufacturers advise of a tyre pressure that is best for the tyre life.
It has always been known that running tyres at minimum 4-5 psi above the vehicle manufacturers placarded pressures gives better mileage from both vehicle and tyres plus better handling usually.
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AnswerID: 419203

Reply By: Cruiser 2091 - Wednesday, Jun 02, 2010 at 10:07

Wednesday, Jun 02, 2010 at 10:07
It is not only manufacturers tyre pressures that are ignored.

Manufacturers often fit glow plugs to diesels which are often ignored.

But the worst case I think was when some people purposely removed thermostats claiming that it gave better cooling.

Ask anyone from the aftermarket dealers or even Exploroz, the manufacturers are wrong. New vehicles are no good but if you fit bigger, wider tyres a suspension lift, aftermarket turbo, new exhaust, oil and fuel additives etc, etc then everything will be ok.

I've gotta go, I'm on my way to Supercheap
AnswerID: 419212

Reply By: Tenpounder (SA) - Wednesday, Jun 02, 2010 at 10:44

Wednesday, Jun 02, 2010 at 10:44
An interesting point: my 90 series Prado nominates 180kpa as the cold tyre pressure: that's 26psi in my language. I would not dream of running such low pressures, and most people talk in terms of the high 30s, including my tyre dealer.
Another consideration: are the tyres fitted now the same as the original tyres fitted by the manufacturer? for example, if you replace Passenger Construction tyres (as fitted to the Prado when new) with Light Truck tyres, you are bound to receive advice to run higher pressures. Of course, if you really want to stick 100% to the manufacturer's preferences, then perhaps you wouldn't move away from the Dunlop Grandtreks fitted in the factory.
I am pretty sure that, at 26psi, my Prado tyres would run pretty warm when loaded up and travelling at highway speeds in summer! - forget about the 4 psi rule (ie if a tyre runs more than 4 psi higher when hot than the measured pressure when cold, then it is underinflated.
When I was young, all tyres were crossply tube type tyres, and that's a different kettle of fish altogether.
AnswerID: 419215

Follow Up By: mikehzz - Wednesday, Jun 02, 2010 at 11:24

Wednesday, Jun 02, 2010 at 11:24
I had a 98 Pathfinder with Uniroyal Laredo A/T tyres on it. They were pretty useless at stopping on a wet road especially at high pressures because the rubber was so hard. I used to run them at 26 psi and got 120,000 kms out of them. I like the more comfortable ride and. I just traded the car with 360,000 kms on it and it had no rattles. Most of the 'bushies' I have talked to seem to think that we run too high a pressure all the time. Anyway, recommended will do me although I take on board others experiences. Cheers
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Reply By: gbc - Wednesday, Jun 02, 2010 at 12:30

Wednesday, Jun 02, 2010 at 12:30
29 lb is the max I run in the front of the colorado (200 kpa as per specs) and I'm pretty sure I carry a whole lot more weight than any prado.

Try doing what the manufacturer recommends for a while - you might get a pleasant surprise.

Tyres aren't made the same any more - why run the same pressures as the seventies?
AnswerID: 419226

Follow Up By: Lex M (Brisbane) - Wednesday, Jun 02, 2010 at 17:03

Wednesday, Jun 02, 2010 at 17:03
Surely you're not saying the car manufacturers knows what they're talking about. Wash your mouth out. :-)
FollowupID: 689413

Reply By: Member -Dodger - Wednesday, Jun 02, 2010 at 16:39

Wednesday, Jun 02, 2010 at 16:39
Often the placard gives a loaded pressure as well.
If not give the recommended pressures a go as per manufacturer of the vehicle. After all they spend millions of $ on development of the vehicle.
I am one of those that believe in lower tyre pressures on rough corrugated roads with a corresponding drop in speed.
And the tyre Rule is 4psi for passenger car tyres and 6psi for 4wd type or LT tyres.
I also stop every 2 hrs or sometimes even less on rough roads this then gives not only the tyres a chance to cool down but also the shocks and many other components a rest including passengers and myself.
I used to have a handle on life, but it broke.

Cheers Dodg.

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AnswerID: 419255

Follow Up By: Tenpounder (SA) - Wednesday, Jun 02, 2010 at 17:04

Wednesday, Jun 02, 2010 at 17:04
Hi. I don't pretend to know the answers: I have Tyredog sensors, and I notice that, when loaded and travelling at highway speed in warm weather, and with tyres around 40psi, that the hot running pressure rises by up to 8 degrees. This seems to mean that, to keep in synch with the 6 psi rule (which I hadn't heard of, only the 4psi rule) I'd have to go up to maybe 45psi plus.
I too go for low pressure on rough roads, especially where hard stone (gibber etc) is involved.
But for me to accept Toyota (26psi) means I would have to ignore all the other advice (tyre manufacturer, tyre dealer and 'learned articles' in the 4WD press). I am also aware that Toyota gives just one pressure figure, regardless of load, which doesn't gell with me.
If I have been running pressures too high, then how come I have not experienced tyre crown wear, rather then even wear?
I suspect that a simple 'one size fits all' answer isn't the way to go, but that we should all use common sense to choose pressure, depending on load, speed, type of tyre and particularly road conditions.
FollowupID: 689414

Follow Up By: Tenpounder (SA) - Wednesday, Jun 02, 2010 at 17:05

Wednesday, Jun 02, 2010 at 17:05
Oops. instead of "rises by up to 8 degrees", I should have said "rises by up to 8 psi".
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Reply By: Fatso - Wednesday, Jun 02, 2010 at 18:11

Wednesday, Jun 02, 2010 at 18:11
I am no expert on this subject either.
But an uncle of mine was. He was at one stage in his life the managing director of Dunlop South Pacific. He started as a messenger boy in a small country Dunlop dealership & made his way to the top of Dunlop when it was at its peak. This was in the days when a manager actually had to know what the product the company sold was.
On the way through his career he wrote many text books gave presentations on tyres. At the time he was probably one of the world most knowledgeable tyre people.
When I got my first car in 1980 (yes I know that is a long time ago but it did have steel belted radial tyres) he was passing through to Bougainville to sort out some tyres issues the mine was having with heavy machinery.
He went into Dunlop IBC (unlike modern directors he knew where it was & knew most of the staff) & got me a pressure gauge & told me to run the tyre pressure at the vehicle manufacturers recommended pressure always.
This he said prolonged tyre life & gave a better ride.
I believed him then & even though he is long dead I still do..
AnswerID: 419268

Follow Up By: Tenpounder (SA) - Wednesday, Jun 02, 2010 at 18:20

Wednesday, Jun 02, 2010 at 18:20
Hang on, Fatso: 1980 was only yesterday. My first steel belted radials were in the mid 60s.
But all this really makes you wonder, doesn't it? How much sceince is there around and how much 'folk lore'?
FollowupID: 689426

Reply By: teabags - Wednesday, Jun 02, 2010 at 18:30

Wednesday, Jun 02, 2010 at 18:30
Had new rubber fitted to my NM pajero a few years ago at one of the big dealers. They said that if I didn't run at least 50psi they would be shot in 10,000 k's. (Mitsubishi recommend 29psi). Left the dealers and the car was almost undriveable. Stopped and checked the pressures, every one different ranging from 55 to 68psi. Let them down to recommended 29psi and when I sold the car after 75,000ks the tyres still had plenty of tread left and were worn very evenly.
Interesting point. These tyres were not LT and manufactures specifications stated maximum pressure of 41psi. Have an accident with the tyre dealers pressures and you would have some explaining to do to police and your insurance would wipe you.
Have tested the 6psi rule and it worked perfectly at manufacturers recommendation.
AnswerID: 419273

Reply By: Mike DiD - Wednesday, Jun 02, 2010 at 22:22

Wednesday, Jun 02, 2010 at 22:22
If you don't use the fuel recommended by the car manufacturer, they say you will void the warranty.

If you don't use the lubricants recommended by the car manufacturer, they say you will void the warranty.

Why is it that dealer service departments can consistently inflate tyres way beyond the manufacturer's ratings, causing them to be slippery on wet roads, yet still get away with it for decades ?
AnswerID: 419311

Follow Up By: Tenpounder (SA) - Wednesday, Jun 02, 2010 at 23:19

Wednesday, Jun 02, 2010 at 23:19
Bear in mind that tyres are excluded from the vehicle manufacturer's warranty. Perhaps that frees the dealers from sticking to the manufacturer's misguided ideas about tyre pressures?
I have never found a dealer who inflates tyres 'way beyond the manufacturer's ratings', and certainly not enough to make them unsafe. What are they 'getting away with', anyway??
FollowupID: 689472

Follow Up By: mikehzz - Wednesday, Jun 02, 2010 at 23:33

Wednesday, Jun 02, 2010 at 23:33
Well I brought this up because I took my wifes vw to the dealer for a service and drove away feeling like I was driving Fred Flintstones car with rocks instead of rubber. As a side issue, what a ripoff dealer services are...ouch.
FollowupID: 689474

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