Neighbor forgot the oil

[Ross]

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The max tire pressure on the sidewall of the tire is just that, the max pressure the tire can be at, be it hot or cold; it is not the "max cold tire pressure."

[/QB]

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It's my understanding that the max pressure on the sidewall is THE MAX COLD PRESSURE. Tires are designed to go above the limit as the tire heats up.

But I could be wrong!
http://www.handymanusa.com/articles/tire.html

[ June 11, 2004, 04:52 AM: Message edited by: Ross ]

 

[Palut]

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Originally posted by Ross:

quote:

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The max tire pressure on the sidewall of the tire is just that, the max pressure the tire can be at, be it hot or cold; it is not the "max cold tire pressure."

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It's my understanding that the max pressure on the sidewall is THE MAX COLD PRESSURE. Tires are designed to go above the limit as the tire heats up.

But I could be wrong!
http://www.handymanusa.com/articles/tire.html [/QB]

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I'm pretty sure you're right. If I have to inflate my tires warm, I inflate them to roughly 5 psi over what the side of the tire says, and I don't notice a rough ride at all!

 

[Matt89]

My Chevy Impala doesn't have the 'best' handling to begin with, but I find that the recommended pressure of 30 PSI is best.

The tires I'm running (Goodyear Regatta 2's) are a hard compound w/ long treadlife, and seem to give up a lot of grip at 32 psi or above in my application. The difference is noticeable when taking "off ramps" at a higher than reasonable speed

 

[brad_d]

I had always been under the impression that a higher-than-optimal tire pressure would adversely affect handling and grip. Is this not accurate?

I fail to understand how one can read "MAXIMUM PRESSURE 44 PSI" (or whatever value) on a tire sidewall and conclude that 44 psi is in any way recommended by the tire maker. The tire companies themselves (all that I have checked) recommend using the pressure specified by the car maker on the door sticker.

Bridgestone/Firestone (as a random example) state on their website:

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Many people ask "what air pressures do you (meaning tire companies) recommend for cars under normal conditions?" The answer is "we recommend what the vehicle manufacturer recommends."

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A bit higher up in that same article, they say regarding high-speed driving (without defining "high speed"):

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For continuous high speed driving, tire pressures should be increased by 3 to 5psi above the normal cold inflation recommended. However, for passenger tires, never exceed the maximum inflation pressure molded on the sidewall. ... Any recommended front to rear pressure differential should be maintained.

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Yes, I will agree than many people run their tire pressures too low. What has been implied in a few posts here is that folks who fill their tires to the door placard's recommendation should be counted in that "too low" group; this I do not agree with.

 

[rpn453]

Many of you are missing what these ratings are all about. A tire's load capacity increases with tire pressure. The tire is rated for a maximum load at the maximum tire pressure. Both of these numbers can be found on the side of the tire. Most people will never come close to the maximum load of the tire, and most cars would have their GAWR's exceeded long before the maximum tire load is exceeded. The engineers that chose the car manufacturers' recommended inflation pressures did so based on expected loading, and it's a compromise of handling, tire life/wear, ride, speed handling ability, safety, and fuel economy. I like my tires a little stiffer, so I usually run 35 to 38 psi in front and about 30 psi in back. I use higher pressures in the front than the back because my car has a 61/39 weight distribution and I rarely put any significant weight in the back.

Inflate the tire to 44psi (or whatever it says) if the tires are at maximum load, but if you put a set of car tires on a powerful 200lb go cart you could probably run 5psi and go 90mph all day in hot weather without a problem. If you used 44psi you'd have a very rough ride.

[ June 11, 2004, 10:13 PM: Message edited by: rpn453 ]

 

[labman]

For best performance and wear, match the pressure to the load and keep the tread flat on the road. Too high of pressure, and the center bulges out, too low, and the center doesn't fully contact the road.

 

[ChrisW]

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Originally posted by labman:
For best performance and wear, match the pressure to the load and keep the tread flat on the road. Too high of pressure, and the center bulges out, too low, and the center doesn't fully contact the road.

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and improper contact of the tire because of miscalculation of load based on inflation pressure can lead to less than optimal tire conditions in the wet. Tirerack has a good picture showing the difference between a properly infalted tire in the wet and too high and too low.

Tirerack wet tire inflation performance

Dry performance

edit: also taken from bridgestone website:
"The vehicle manufacturer's specification of tire pressure is limited to that particular vehicle and takes into account the vehicle loading, ride, and handling characteristics, among other criteria. Since there potentially several possible vehicle applications for any given tire size, note that a vehicle manufacturer may choose a different inflation pressure specification for that same size tire for a different vehicle. Therefore, always keep the vehicle manufacturer's recommended air pressure in all your tires, including the spare. For normal operation, follow pressure recommendations in owner’s manual, on vehicle tire information placard, or on the certification label.
Note: The operating pressure is based on a number of factors (like load), and so may not be the same as the maximum inflation pressure on the tire’s sidewall. For example, the U.S. Department of Transportation now allows 240 kPa (35 psi), 300 kPA (44 psi), or 350 kPa (51 psi) inflation pressures for standard load tires, but, no increase in the tire’s load [from that of the 240 kPa (35 psi) pressure] is allowed."

My thinking is this: tire engineers design tires. Sure, they take into account what they may expect the tire's app to be applied to, but how can they (the "max" marking on the sidewall) be representative of what the tire pressure ought to be at if the tire engineers do not know exactly what the app is, and the load etc? This is why the tire engineers reccomend the reccomendation of the car manufacture engineers.

I will agree that many car makes out there have tire pressures reccomended for the best balance between comfort rather than tire life or such, but I don't think a car manufacturer would reccomend a potentially dangerous and low tire pressure. Running 40 psi may seem safer by word of mouth from a tire dealer, but this does not automatically make the car manufacturers reccomendation [of say, 32psi] unsafe; a lot of calculations [load, avg speed, ride quality etc] went into that figure. (with the exception of the ford and firestone deal, i still dont really know where the fault really lies)

[ June 12, 2004, 03:23 AM: Message edited by: ChrisW ]

 

[XS650]

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Originally posted by ChrisW:
I will agree that many car makes out there have tire pressures reccomended for the best balance between comfort rather than tire life or such, but I don't think a car manufacturer would reccomend a potentially dangerous and low tire pressure. Running 40 psi may seem safer by word of mouth from a tire dealer, but this does not automatically make the car manufacturers reccomendation [of say, 32psi] unsafe; a lot of calculations [load, avg speed, ride quality etc] went into that figure. (with the exception of the ford and firestone deal, i still dont really know where the fault really lies)

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It's a shared blame, mostly Firestone's fault.

Ford is partly to blame for making the Exploder easy to roll over. Partly because of the high CG, partly because of the primitive suspension geometry. The rollover problem was minor until a tire blew and the lousy SUV driver lost control.

That said, Ford Exploders with tires other than Firestone didn't have the problem to any significant extent.

Firestone whined that Ford recommended too low a tire pressure. But, Fords recommended tire pressure still provided adequate weight capacity according to specs for that size and type of tire.

During the peak of the Ford Exploder roll overs, I heard a field reporter for KGO radio giving an accident report. He reported that a Ford Explorer with Firestone tires had rolled over. The pompous @ss talking head (Pete Wilson IIRC) chastized the reporter for jumping to conslusions about the detais. The reporter replied, "Well Pete, the SUV is easy to recognize as a Ford Explorer, even though it is parked on its roof. And even though the tire I'm looking at 4 feet off the ground and 2 feet from my face is pretty well shredded, It distinctly says 'Firestone' on the sidewall. Back to you Pete."

 

[1sttruck]

Another potential problem to consider for 4WD vehicles is the practice of using very low tire pressures for maximum traction when going offroad. I have a 4wd pickup that when loaded for vacation and traveling at 70 mph on the highway needs 70 psi on the front tires and 65 psi in the rear. The brochure from the tire company states to add 10 psi for speeds over 65 mph. So far I haven't found a manual or small battery powered pump that can inflate the tire from say 40 psi to 70 psi in a reasonable period of time, so I don't let the air out. For those who do how do they reinflate for high speed driving with loads ? I've been looking at the 2 gal or so air tanks that seem to be designed for air poweed tools.

Another consideration is something that I noticed when looking at the tire pressures needed for different loads. Wih a maximum load in the bed I need 80 psi, I also need to add 10 psi for speeds over 65 mph, but since the maximum pressure for the tire is 80 psi one assumes that the tires aren't designed to handle a maximum load with speeds over 65 mph. Makes one wonder about all of the big trailers being towed by pickups at 70mph to 80 mph.