Tire Pressure Inflation - what is too much? - Fuelly Forums

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Old 09-21-2007, 04:32 PM   #1
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Tire Pressure Inflation - what is too much?

http://www.tirerack.com/tires/tirete...e.jsp?techid=1

Disadvantages of Overinflation

An overinflated tire is stiff and unyielding and the size of its footprint in contact with the road is reduced. If a vehicle's tires are overinflated by 6 psi, they could be damaged more easily when encountering potholes or debris in the road, as well as experience irregular tread wear. Higher inflated tires cannot isolate road irregularities as well causing the vehicle to ride harsher and transmit more noise into its interior. 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.

Disadvantages of Underinflation

An underinflated tire can't maintain its shape and becomes flatter than intended while in contact with the road. If a vehicle's tires are underinflated by only 6 psi it could weaken the tire's internal structure and eventually lead to tire failure. Lower inflation pressures will allow more deflection as the tire rolls. This will build up more internal heat, increase rolling resistance (causing a reduction in fuel economy of up to 5%) and reduce the tire's tread life by as much as 25% while increasing the probability of irregular treadwear. Drivers would also find a noteworthy loss of steering precision and cornering stability. While 6 psi doesn't seem excessively low, it typically represents about 20% of a passenger car tire's recommended pressure.

Advantages of Correct Tire Inflation

Maintaining correct tire inflation pressure helps optimize tire performance and fuel economy. Correct tire inflation pressure allows drivers to experience tire comfort, durability and performance designed to match the needs of their vehicles. Tire deflection (the tread and sidewall flexing where the tread comes into contact with the road) will remain as originally designed and excessive sidewall flexing and tread squirm will be avoided. Heat buildup will be managed and rolling resistance will be appropriate. Proper tire inflation pressure also stabilizes the tire's structure, blending the tire's responsiveness, traction and handling.
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Old 09-22-2007, 06:48 AM   #2
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I have to disagree with the claim of irregular wear patterns. I've had tires inflated to 60 psi for 10's of thousands of miles with no irregular wear patterns showing up. I know of a guy in northern IL that has ~85K miles on the stock tires that came with his '05 Accord that seem to have several K miles left on them.
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Old 09-22-2007, 06:50 AM   #3
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Read this thread.
http://www.gassavers.org/showthread.php?t=803
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Old 09-22-2007, 07:16 AM   #4
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I've been running 60 psi on the word of a few fuel economy minded drivers
It goes against what we've been told and how we've been taught to maintain our vehicles- BUT it works . I've been checking the tires at least 3 times per week (pressure and tread depth with a rotation every 3500 mi) and am now at 8k miles with no discernable treadware issues. I had a really large bump in mpg at @ 55-60 psi - so thats where I run em . as always, ymmv
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Old 09-22-2007, 05:05 PM   #5
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Yeah, I read that article. Pretty nutz. What about my front tires. The sidewall is 35. You think I do 45? I think right now they're at 39. I'm gonna put my rears up to 50. They are max rated to 44.
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Old 09-22-2007, 08:57 PM   #6
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1993CivicVX -

Here is a conservative source :

The wheel and tyre Bible
http://www.carbibles.com/tyre_bible.html

The Max. Pressure -10% theory.
http://www.carbibles.com/tyre_bible_pg2.html
Quote:
Every tyre has a maximum inflation pressure stamped on the side somewhere. This is the maximum pressure the tyre can safely achieve under load. It is not the pressure you should inflate them to.

Having said this, I've given up using the door pillar sticker as my starting point and instead use the max.pressure-10% theory. According to the wags on many internet forums you can get the best performance by inflating them to 10% less than their recommended maximum pressure (the tyres, not the wags - they already haves inflated egos). It's a vague rule of thumb, and given that every car is different in weight and handling, it's a bit of a sledgehammer approach. But from my experience it does seem to provide a better starting point for adjusting tyre pressures. So to go back to my Subaru Impreza example, the maximum pressure on my Yokohama tyres is 44psi. 10% of that is 4.4, so 44-4.4=39.6psi which is about where I ended up. On my Element, the maximum pressure is 40psi so the 10% rule started me out at 36psi. I added one more to see what happened and it got better. Going up to 38psi and it definitely went off the boil, so for my vehicle and my driving style, 37psi on the Element was the sweet spot.
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Old 09-22-2007, 09:21 PM   #7
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Cyclists probably think about this more than any of you guys would ever need to. Different PSI for a road race verses a time trial or wet vs dry. Usually it is only inexperienced time trialers or triathletes that overinflate. For cycling tyres, the adhesion is a function of contact time and overinflated tyres can bounce loose of contact easier. That takes a lot of skin off your body - they shave their legs for a reason.

At some point the handling of any overinflated tyre will degrade. I would never exceed the maximum sidewall pressure. I'll respect the legal opinion of the tyre manufacturer on what the max should be and my insurance company shouldn't be able to find any issues with that.
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Old 09-22-2007, 10:16 PM   #8
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Cyclist's tires also aren't radially belted -- the handling change is very different as the bias threading allows the tire/tube to balloon :/

For a TT on an unknown track, that makes sense given that it's easier to catch a bump, loft/break traction and bad things come of that.... I've read about the speed/challenge distance guys over inflating the hell out of their tires - especially on a velodrome track -- but I'm talking about the 60+mph cyclists It's also been suggested to shave down rubber tread for shorter use/higher speed runs o.0
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Old 09-23-2007, 07:39 AM   #9
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Originally Posted by 1993CivicVX View Post
Yeah, I read that article. Pretty nutz. What about my front tires. The sidewall is 35. You think I do 45? I think right now they're at 39. I'm gonna put my rears up to 50. They are max rated to 44.
Do a search on posts by krousdb. He achieved tremendous FE in both a Del Sol, & a VX.
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Old 09-23-2007, 07:45 AM   #10
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Quote:
Originally Posted by 1993CivicVX View Post
Yeah, I read that article. Pretty nutz. What about my front tires. The sidewall is 35. You think I do 45? I think right now they're at 39. I'm gonna put my rears up to 50. They are max rated to 44.
I would be careful about putting the rears higher than the fronts. It could cause the rear end to get a little squirly since there usually isn't much weight on the rear of the car. Most manufacturers recommend that the fronts be higher than the rears due to the weight of the engine/transaxle being up front.
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