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Old 05-15-2003, 08:40 AM   #1
mchapman
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Recommended psi verses Max psi.

I read the forums fixed post, "Tire tech" by Luke@tirerack. It was good reading, however, it did not quite answer a question that I have had for 20 years regarding max tire pressure.

Regarding tire inflation technique, the forum post stated, '....recommended tire pressure...cold...'. The problem is that the tires all say, "max tire pressure", instead of 'recommended'. Here's my question. If a tire says 'max 35 psi' and it is 70 degrees cold, parked overnight, etc, and by late afternoon it will be 90 degrees, then; should I fill the tire to 33 psi, so that I do not exceed the max psi later on when the tire heats up?

I have always underinflated my tires by 3 psi from the 'max psi' printed on the tire, in a calculated effort to not exceed the 'max psi' as the tire heats up.
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Old 05-15-2003, 12:02 PM   #2
Venger10
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MAX cold psi means exactly that..that is the most you should inflate the tire to when COLD , it takes into account what tire pressure will be when it warms up
For example , The tires on my WRX said "max cold psi 44" which I did. Next day it was 70+ degrees and when I checked them they were about 55 psi......
As long as you don't exceed the max cold psi rating , the tire should be fine.....

A few years ago I worked at a gas station ..... had a guy come in one day , complaining that his car was riding VERY hard..... said he'd put air in his tires a few weeks before , but since he did not have an air guage , he had to guess by how "hard" the tire felt....
When I check his tires , a couple of them were over 100 psi And this was on a Honda....:smoker2: :smoker2:
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Old 05-15-2003, 01:14 PM   #3
Cy@tirerack
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Ditto

Also figure about 1 psi change for every 10 deg change in temp. Cold pressure is generally based on an ambient temperature of 60 deg Fahrenheit.

So if car has been sitting out in the sun with an ambient temperature of 80 deg Fahrenheit, then when you check and adjust pressure you want to compensate by setting at 2 deg below your intended pressure. So if you want to run 30, inflate to 32.
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Old 05-16-2003, 01:11 AM   #4
mchapman
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Thanks, those two answers were just what I was looking for. Thank you both ever so much.
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Old 05-20-2003, 10:29 AM   #5
marzo7
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You guys are the experts, so I'm a little hesitant to disagree, but.....it seems strange to me that the maximum pressure stated on the sidewall would be for a "cold" pressure. If that was the case, then it would not really be a "maximum" at all, just another "recommendation".

Presumably a tire manufacturer has done some testing to determine what is the maximum safe pressure that a tire can sustain. By definition, this would be a "hot" pressure. Why then would the manufacturer fool around with listing a supposed maximum cold pressure on the sidewall, making the consumer guess as to how much air the tires were designed to sustain safely?

A maximum of 44 psi hot would be just that, the maximum, no if's and's or but's. A "maximum" of 44 psi cold is totally meaningless. Why would the manufacturer even bother to list such a thing?
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Old 05-20-2003, 11:58 AM   #6
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OK, I did a bit of research, and of course you guys are right. I still think it doesn't make much sense, but at least now I know why: it's government regulations that mandate the rating!

FWIW, every tire I've owned has simply stated "Max. load of xx at max. pressure of xx." IMO, all manufacturers should do like that of Venger10's tires and explicitly state that the max. pressure is "cold".
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Old 05-20-2003, 03:38 PM   #7
Venger10
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They do.......

Its further around the edge of the tire and it should be in () << like so.....

(Max cold pressure 44 Psi)


Every tire I've seen had that on the side...... :alien2:
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Old 05-20-2003, 04:00 PM   #8
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Hmm... I just double-double-checked both sets of tires in my garage (Kumho Ecsta 712 and Toyo Proxes RA1). Nope, neither make any mention of whether the max. pressure is cold or hot (unless they've molded it into the tread in braille ).

I'll check our BF Goodrich Long Trails when my wife gets home, but like I said, I've never seen it before...
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Old 05-20-2003, 06:55 PM   #9
Venger10
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How weird...... I've never seen a tire without them.
My Potenza's had it , my Eagle GS-Z's had it , my Kumho's had it , I just looked outside and my Signet DH-60's have it .
Sure you are looking in the right place?? its VERY close to the edge of the rim.

Also , I'm thinking perhaps that maybe only H and up rated tires may have it on there....

Inflation pressure is more crucial on a performance tire than on a regular Passenger car tire :smoka:
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Old 05-21-2003, 12:21 AM   #10
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Well, I just checked the Long Trails, and nope, no mention of the word "cold".

All three tires I've listed say the same thing: "Max load of xxxx lbs at max pressure of xx psi". Absolutely no mention of the word "cold".

I don't think speed rating has anything to do with it: my Kumhos are V-rated and the Toyos are Z-rated.

The only thing I can think of is that manufacturers make a different production run for Canada (which is where I am). Seems unlikely, but maybe that's it. Now that I think about it, my tires also state the maximum load in kilograms and the maximum pressure in kilopascals. Is that the case in the U.S. also?
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Old 05-21-2003, 08:45 PM   #11
Venger10
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Yes , they do state Kpa and max load in kilo's.......

Maybe they don't think inclusion of the word COLD is quite as important in Canada.... :alien2: :alien2:
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Old 05-21-2003, 09:00 PM   #12
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Some background on maximum tire pressure

Perhaps I can help explain.

Tires are standardized. In the US the standards organization is the Tire and Rim Association (TRA). In Europe, it's the European Tire and Rim Technical Organization (ETRTO). There are others.

It is these bodies that set the nominal dimensions AND the loading standards, which includes the maximum psi. It is a US government regulation that the maximum load and the maximum pressure be stamped on the sidewall and it is must conform to one of these standards.

In all cases, these pressures are specified as cold. It is the tire manufacturer's responsibility to account for the pressure build up in their design. Doesn't matter how much it is, but it must be factored in.

For practical matters, the static bursting pressure of passenger car tires is well over 100 psi. So 44 psi, which is what is now standard max pressure on most passenger car tires, is well within design capabilities.

Hope this helps.
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Old 05-28-2003, 04:20 PM   #13
marzo7
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Thanks CapriRacer...

Not to beat this to death, but I just had a look at the two sets of winter tires buried in the corner of my garage:

Bridgestone Blizzak LM-22 - no mention of the word "cold"

Yokohama Geolandar I/T - well whaddaya know, yep they specify that the maximum pressure is 50 psi COLD.

For me, that's only one out of five that specifically indicates "cold". I wonder why there isn't more consistency in the labelling?
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Old 05-28-2003, 08:34 PM   #14
Venger10
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Quote:
Originally posted by marzo7
Thanks CapriRacer...

Not to beat this to death, but I just had a look at the two sets of winter tires buried in the corner of my garage:

Bridgestone Blizzak LM-22 - no mention of the word "cold"

Yokohama Geolandar I/T - well whaddaya know, yep they specify that the maximum pressure is 50 psi COLD.

For me, that's only one out of five that specifically indicates "cold". I wonder why there isn't more consistency in the labelling?
Its a government thing......
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Old 08-15-2003, 02:39 PM   #15
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Re: Recommended psi verses Max psi.

Venger10, you said earlier in this post that you had Signet DH-60's? I just bought a 2000 Grand Am SE1, I am trying to find some information on my tires that came on it. It says Signet, then Dark Horse on it. I have looked all over on Google.com trying to find anything about tires and Signet, and Dark Horse and I keep getting nothing. Is Signet the actual brand name then? Or are they made by another company like Pirelli, or something? I did find a Korean website, http://www.nexentire.co.kr/business-...log_radial.htm that showed some tires, and had Dark Horse next to them, but I am not sure if these are the same ones... I am not home right now, and did not drive that car here, so I can't go and check to see anything more about it right now.
Mainly, I am just trying to get some information on them to see if they are good tires. They really look nice...

-captain_tinker
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