Note: I posted this in another thread, but I realized it makes more sense to just post it here and link to it when it's needed in other threads. I plan to edit this as time goes on and I refine it.
Tire Air Pressure Myths and Facts
A canned post by theholycow
Originally posted at
http://www.gassavers.org/showthread.php?t=7712
Please include the link if you post/distribute this elsewhere.
Edit: Some decent numbers can be found at
http://www.metrompg.com/posts/tire-p...resistance.htm
Increased tire pressure is a cure-all for problems, and generally an improvement even when there are not problems. I have been driving with greatly increased tire pressure for hundreds of thousands of miles, and have not suffered ANY consequences, though other drivers with other vehicles could. I have only benefitted from it.
There are limits, though. You should
never significantly exceed the tire's maximum pressure rating, which is stamped on the side of the tire (often next to its maximum load rating, which requires the maximum pressure). If you add pressure and find that your handling has suffered or your ride is terribly harsh, you should reduce pressure until that issue is gone. Those things are very important limits. If you exceed them, you could possibly cause a tire failure (though I doubt it); however, real consequences may include center wear, possible liability in an accident, and sketchy handling that could cause an accident.
Within those limits, you can find the following advantages:
- Decreased rolling resistance which means increased gas mileage
- Better handling due to reduced sideways curling of the tire under the lateral load of a hard curve
- Better handling due to quicker response from less tire flex
- Better wear, unless you normally wear tires perfectly evenly and always get more than their treadwear warranty out of them
If that's all so great, why do car manufacturers not recommend the full pressure of the tire? It's because they recommend the lowest pressure that their legal department approves based on industry-standard load-inflation charts. For any amount of load on a tire, there's a minimum safe inflation which provides the softest ride.
To sell cars, they want the ride as soft and compliant as possible when you test-drive it. More pressure isn't bad, it's just not traditional to try to sell a car that way.
Modern automotive tubeless radial tires are NOT subject to the same types of failure as the bicycle tires you remember popping as a child. They won't blow off the rim (unless you use way, way more than their maximum rated pressure). They won't pop when you hit a bump. They won't explode in your face.
They almost always fail from underinflation (which causes overheating) or a break in the sidewall caused by an impact (which is less likely to happen if you have more pressure preventing the bump from squeezing the sidewall against the rim).
http://www.tirerack.com/tires/tirete...e.jsp?techid=1 has a section cautioning against overinflation which includes this:
Quote:
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However, higher inflation pressures reduce rolling resistance slightly and typically provide a slight improvement in steering response and cornering stability. This is why participants who use street tires in autocrosses, track events and road races run higher than normal inflation pressures.
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This site for police officers has an article about tire pressure:
http://www.officer.com/article/artic...on=19&id=27281
Here's selected pieces:
Quote:
Higher pressure results in better performance, decreased tire wear, and it lessens your chance of hydroplaning at a given speed. [...]
Many agencies maintain tire pressure at 35 psi since this is what is listed in the owner's manual and on the door placard. [...] You are not looking for a soft and cushy ride, you want performance. [...]
The tires will not balloon out creating a peak in the center portion of the tread when tire pressure is above 35 psi. There is a steel belt that prevents this from happening. Also, you are not overstressing the tire with higher pressure, and the tire will not be forced off the rim with higher pressure. [...]
If you were able to watch a tire as it travels across the ground at high speed, you would see that it deflects to one side during cornering. The faster you are going through a corner, the more tire deflection you get. As the tire deflects over onto the sidewall, you get less traction and more of a tendency to understeer or oversteer. [...] Higher pressure keeps the tire from deflecting onto the sidewall as much, which keeps more of the treaded portion on the road. A good demonstration for EVOC instructors is to have students drive a high-speed course in a vehicle with 32 to 35 psi. Then have them run the same course with 44 to 50 psi in the tires. The student will experience a marked difference in performance. [...]
Tire manufactures and the Association of Law Enforcement Emergency Response Trainers International (ALERT) have shown that tires have more of a tendency to hydroplane when pressure is low. [...]
In 1999 the San Jose Police Department realized a significant cost savings by increasing the pressure in the training fleet to 50 psi. They soon followed up by increasing the pressure in the patrol fleet to 44 psi. [...]
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Two vehicles on which I've had much (but not all) of the aforementioned hundreds of thousands of miles experience:
I had a 1997 Pontiac Grand Am SE V6 with P205/55R16 tires. I bought some Bridgestone "Turanza T" tires, which lasted about 70,000 miles (that was less than 3 years for me) before the sidewalls were cracked and the tread was worn at the corners. I ran them at the pressure printed on the car's door post, which may have been 30 or 35 psi. I replaced them with the same, but inflated the new ones to the tire's maximum pressure, 44psi. Handling went from soft and sloppy to responsive and decent. Ride did not suffer. They wore perfectly evenly and had 80,000 miles on them when I sold the car -- and they were still good for more miles.
On my 2002 GMC Sierra 1500, I keep my tires inflated to their full 80 psi rating. Sometimes I run the rear tires a little lower, because the handling gets sketchy with the bed empty and the road surface slick. Other than that, I get long, even wear and decent handling.
6/18/2008: New data makes me question my
tire width theories, but supports higher inflation pressure. A
post by user slogfilet with a
very interesting link shows that higher inflation does NOT reduce contact patch. I can't say for sure that the new data is correct, or even analyzed correctly, nor can I say if it's wrong. I hope to do some of my own testing.
It would also suggest that the theories about
how increased inflation helps FE may be wrong, but that only affects the explanation behind the observations; hard data from users on this forum shows that increased inflation helps FE, and that hard data is undeniable.
Tire pressure myths, facts, observations, and improvements (canned post)
Glad to hear of your good results!
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