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Discussion Starter · #1 ·
Hello Everyone

I've noticed lately that when my bride takes her car to the local oil change establishment, her vehicle comes back with about 40psi in each tire.
I tell her to never let them touch the tires because some genius is convinced that the max pressure indicated on the sidewall is what you are suppose to fill to.

I took my 9000 in today for two new Michelin MX4 tires for the rear...guess what

When I got home, I checked the tire pressure cold and 40psi. I called the manager and explained how, I was taught, the pressure should be 32psi and not the max of 40psi. He told me they fill all tires at 40psi.

Have I missed something technologically over the past 20 years???


What say you, folks?

wherewolfe
 

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Hey whats up wolf? I always tell them to look at the Manufactores stick on the inside of the rear door on the passengers side ...I say to them and I quote "See it says right here what the correct tire PSI should be for 1-2 2-3 3-4 4-5 people and there is never anymore then 1-3 people in my car so I dont need the max inflation listed, just put in what it says for 2-3 people...no more no less".
They tend to get it right then.
I also make them put it into there computers so when I come back it states it in black and white for them.
 

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Tyre (tire) places in the UK often put too much pressure in after replacing tyres.
I think it is because the car then feels really good as you drive out of their premises (light responsive steering etc) so you feel that you got something worthwhile for your money .... only to have a shock later at the first sharp bend in the rain.
 

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Discussion Starter · #4 ·
Hey Guys!

Thanks for the confirmations. Thought I fell asleep and missed something!

I have got to the point with my Saab that NOBODY
ISSA GONNA TOUCHA MY TIRES. I normally check them weekly after my Saab Bonding Hour Cleanup.
The Michelins seem to respond best with about 30psi in the front and 32psi rear.

As for my wife's car, next time the oil change is due, wherewolfe is going to take it in and make sure they DONNA TOUCHA THE TIRES

hey gundam hows the family??

wherewolfe
 

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Interesting how tire manufacturers are almost always cited as recommending higher tire pressures than the vehicle manufacturer. One motor journo noted that vehicle manufacturers want their cars to ride smoothly , whilst tire manufacturers want their tires to handle and last as best/long as possible. Whilst I agree that 40psi cold is too high, 35 cold or 40 warm is ideal. Under-inflated tires perform poorly (both in terms of braking distance and cornering), wear unevenly and consume more fuel. Tire technology is an extremely advanced science and I would argue that the tire company engineers are better qualified to recommend a suitable tire pressure for their tires than the vehicle manufacturer. In any case many tire manufacturer engineers test their tires with 35psi of nitrogen gas (doesn't change in volume like air does). Its interesting that at most advanced driving courses, the first thing the instructor does is go out to the carpark and take pressure readings of everyone's cars. Most people have their tire under-inflated and instructors always advise higher tire pressures to ensure maximum road-tire contact in all conditions (ever notice how tires squeel in corners when they're under-inflated?).
 

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Discussion Starter · #8 ·
I agree with tire pressure being 35-49 psi HOT.
But cold tire pressure, by my definition, is measured when the car has not been driven in several hours/first thing in the morning.

If I check my pressure after a one hour trip, the
range is about 36psi based on the cold pressure being 32psi.

I hesitate to think what the pressure would be hot when tires are filled to 40psi cold.

The amazing thing is that the quick lubes, tire store chains instruct their people to inflate to 40psi. Shutter to think how many accidents have occurred on wet or snowy pavement due to overinflation

wherewolfe
 

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I think you will find that the car makers work VERY closely with the tyre manufacturers when choosing types and setting pressures - I would ALWAYS go by the car handbook and not by some generic tyre shop wall chart.

Examples of close cooperation :
Ford/Goodyear - the 70's Zephyr had special rear tyres : standard tread pattern but stickier rubber : an attempt to keep the back of the car under control and far cheaper than re-engineering the car.
Vauxhall/Bridgestone - Special compound front and rear for Potenzas fitted to VX220 sports cars.

The alarming thing is that the independent tyre shops often don't know about the "specials" and will fit standard tyres when replacing the originals.

(In a different incarnation I worked for Goodyear checking the vulcanisation of the tyre rubber)
 
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