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Author Topic:   ==> tire pressure: door jam max psi vs. tire rating...
Bill
unregistered
posted November 19, 1999 08:45 PM           Edit/Delete Message Reply w/Quote
I just put new tires on my car and the door jam says 31 max psi (for the stock Michelins) and 44 psi for the new yokohamas. Which should i use? 37 seems ok but im not sure it's safe or correct.

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Vin
unregistered
posted November 20, 1999 07:58 AM           Edit/Delete Message Reply w/Quote
Always use the car manfacturer's recommended psi. They know your car best. Read the manual thoroughly - it might even suggest different psi for different driving. My Audi recommends 32ps1 at all 4 corners most of the time but recommends adding 3 psi for heavy loads (5 people & full trunk) and also addning 3 psi if I'm specifically running snow tires.

You can always tweek yourself. I always keep my pressures 2psi above just because I do a lot of highway driving. 2psi is almost negligible but it's supposed to slightly favor better fuel economy.

The max pressure will almost never be used. Pressures that high in a tire cause the tire to be more susceptible to damage. Impacts at highway speeds allow a greater chance a blowout.

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Bill
unregistered
posted November 21, 1999 04:00 PM           Edit/Delete Message Reply w/Quote
Thanx. Any idea on how much the tire pressure increases once you drive?

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tiretech2
unregistered
posted November 23, 1999 05:39 AM           Edit/Delete Message Reply w/Quote
Bill
Over the years I still can't believe that people think that the car makers konw more about tires than the tire people. Go by what the sidewall of the tire reads not the door jam. Run about 5-7 psi less than the sidwall max with the max load. I could get into great detail on how to correcctly figure psi settings but this will work for the average vehicle and tire. Think about this the key to every tire is correct psi. If you set the psi to low than you risk the tire coming apart. Now how is the car maker going to figure the correct psi for every tire that could be installed on the car. Go by what the tire people tell you. Find someone that has been in tires for awhile. That door jam thing has had me going nuts for 26 years now.
TireTech2
1stoptireshop.com

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Stu
unregistered
posted November 23, 1999 01:22 PM           Edit/Delete Message Reply w/Quote
I'm a tire engineer, go with what is on the door jam. If the tire is the same size as what came with the vehicle, the Auto manufacturers and the tire companies spend many hours dialing that pressure in. Having a pressure lower than that recommended pressure could lead to shortened tire life and could pose a hazard. The air in the tire supports the load, so less air and the tire is working harder than it is supposed too. If you would like to have more air in there, go ahead. Usually the ride degrades badly.

The sidewall markings on the tire for inflation are tire industry standards based on size and usage. In other words they are regulations from the government for Maximum inflation and load, they are not vehicle specific.

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Bill
unregistered
posted November 25, 1999 12:42 AM           Edit/Delete Message Reply w/Quote
Based on current input i have deduced:

The auto manuf does not know the new tire and the tire manuf doesn't know the auto.

They both only know the maximum load they will exert and the maximum load they can receive.

The tire sidewall is the MAXIMUM psi of the tire weight it's components can withstand, and the door jam is the PREFERRED psi based on the stock tire.

You see, this will never have an answer because everyone has covered their butt so you can't sue them.

Well, since half said tire and half said door jam and the tire manuf says 31 psi and the tire manuf says 44....

37 psi it is. until i have a blowout, then i'll try 34.


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tireman9
unregistered
posted December 09, 1999 06:19 AM           Edit/Delete Message Reply w/Quote
Tire mfg do know vehicles and car MFG do know tires. The engineers work together for years developing exactly the right specification for the tire to deliver just the desired balance of ride, handling, traction, fuel economy and 20+ other characteristics for the car in question.
44 psi is the MAX for mounting and it says so on the tire and tire stickers.
The car door jam is 35 psi or a little lower which is the max load inflation and provides a good compromise of the above characteriatics.
Read the owners manual and follow it.
Read the tire safety warning and follow it.
If you are a "tire tech" and don't understand this get another job.

tireman9@hotmailx.com < remove x

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Bill0001
unregistered
posted December 16, 1999 04:04 PM           Edit/Delete Message Reply w/Quote
Tireman9,
The auto manual says replace the stock tires, but i upsized from 195/65 HR15 to 205/60 VR15 and the tires do not come with a manual. Since you seem to know, at what psi do i set my 98 Accord 4cyl sdn? Telling me to read the manual is not really a solution (cop-out comes to mind).

It has Yokohama AVS S-4 205/60 VR15 (stock is Mich Energy MXV4+), the door jam says 31 psi (which is obviously too low when you drive the car) and the tire says 44 psi Max (that's 12 psi variance or almost 25%)

The reason for the questions was to see how tire techs are trained to handle this seemingly simple situation, which happens everday and it appears they are not b/c nobody can give me a straight answer and a psi!

So tireman9, what psi do you put in the tire, if you are the tech!?

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tireman9
unregistered
posted December 19, 1999 05:21 AM           Edit/Delete Message Reply w/Quote
Glad to try and be of help Bill.
First the 44psi is a max to be used while mounting and the recommended max operating inflation is 35 psi except in special situations. The max load capacity is still based on 35psi. The 44 came about because some cars in Europe were getting 37 or 38 etc as spec in an effort to meet the fuel economy standards there. The 44 was set by industry agreement to avoid "inflation war".

OK now for your car. If you just do a simple 1 or 2 size upsize the owner's manual 31 psi recommendation is still valid. A larger tire with the same air will carry more load which means you will probably see a slight improvement in handling. If you want more handling than 31 gives you and are willing to give up some ride you can go up to 35. Much beyond that yoe will start to see diminishing improvement and will start to see wear and other problems etc.

Hope this was of some help.

Yes I am in the tire industry for many years.


tireman9@xhotmail.com < remove x

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Bill0001
unregistered
posted December 23, 1999 03:00 AM           Edit/Delete Message Reply w/Quote
That seems reasonable!

Thank You.

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