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Old 10-27-2008, 06:38 PM   #11 (permalink)
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I'm nor a layer, nor a tire expert.

Over-inflating between placard and sidewall is in safety limits given by constructor and manufacturer.

Over-inflating over sidewall is certainly dangerous under unexperienced people's hands, but can be safely used by experienced people :
Driving Under Pressure (full article) - CleanMPG Forums

Denis.

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Old 10-27-2008, 08:51 PM   #12 (permalink)
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my tires are at 50psi and are rated 51psi. from 35 psi i went to 44 and picked up a little over 1 mpg. i went to 50 psi and saw another 1 mpg. in a 17 city epa 4runner that drives 90 percent city thats a huge gain. i know im getting at least 2 mpg more with 50 psi.

my in car mpg gauge read 16 to 17 mpg before eccmodder and i got it up to 20 mpg before i started logging my mileage on ecomodder. if i drove more highway miles i guarantee you id be pulling 25 mpg in this car but with only a 4 mile commute to work on all 35 mph flat roads in city driving im happy with a 5 mpg gain since february.

with 90 percent highway driving on a road trip in august i pulled over 27 mpg in a 22 mpg epa highway rated car with no mods other than psi and p&g and no instrumentation (scanguage is coming for christmas).

pump those tires up boys!
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Old 10-28-2008, 09:41 AM   #13 (permalink)
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Interesting thread.

I think hyperinflated tires (my definition: tires being inflated past the mfr's maximum) are a big mistake. Sometimes people get myopic about fuel economy and forget that you have to steer, stop and corner. A hyperinflated, or overinflated for the load, tire reduces the tire footprint and changes the whole roadholding dynamic and the way the tires, brakes and suspension work together. In the long run the money you might be saving will just come out of your paycheck in another way, such as in a set of tires much sooner. Or chiropractic visits ( : < ). Or a sudden, devastating tire failure. MetroMPGs second test should help convince anyone that there's a plateau for any tire.

I experimented with my newer pickup and discovered, as MetroMPG did in his latest test, there's a "Three Bears" just right and any gains above that point are fractional. In my case, the truck manufacturer's loaded pressures of 50 psi were it. I didn't see any marked gain by going up another 10 psi to the tire sidewall maximum. It also turns out that the difference between the tire placard max and a slightly lower pressure that offered reasonable ride quality, performance and tire wear was very small. When I upgraded to larger, more farm field friendly tires (taller and slightly wider), I expected to lose a little mpg but I actually gained some, most likely from the "overdrive" effect of taller tires (truck has 4.10 towing gears) that cancelled out the losses due to rolling resistance and gave me a little extra. Surprisingly, the height gain didn't throw the aero off too much, at least at the moderate speeds I cruise at but I did lose noticeably at 70 mph and above. I might be able to get some of that back with a bed cover. Will be doing some coast-down tests next spring to check it all out.
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Old 10-28-2008, 12:38 PM   #14 (permalink)
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heres my contribution

i have mud tires on my daily driver. yeah, i know.... i'm working on it.


anyways, they have a 50 psi max rating. i've been running them at 45 psi with good results. i've noticed my last 2 tanks were about 2.5 mpg lower than normal. so i checked my tire pressure, and they were all at around 33 psi. guess i need to check them more. i know the colder weather made the tires "lose" air, and i'm sure the colder temps are affecting mpg due to longer warmups. but i pumped them back up and waiting until next fill-up to see if it made a difference.
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Old 10-29-2008, 08:15 AM   #15 (permalink)
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Economic sense of high tire pressure

Hey folks,

All this stuff with hyper inflated tires is fine but does it make economic sense ?

Overinflated tires will not last as long as normally inflated ones so while you save gas, you loose tire life ! Time for a reality check maybe

If you really want to save by more rigid tires, get a solid rubber wheel or better yet, a TWHEEL !

Michelin Tweel: en vidéo par Le blog auto: actualités automobile et sport automobile

Cheers

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Old 10-29-2008, 08:54 AM   #16 (permalink)
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Quote:
Originally Posted by Denis View Post
Overinflated tires will not last as long as normally inflated ones so while you save gas, you loose tire life ! Time for a reality check maybe
Salut Denis,

This is sounding more and more like a myth. Every fuel economy enthusiast I know of who overinflated have seen increased tire life and even wear. There are a lot of people overinflating and reporting successful results. Yet, we don't hear about those who overinflated and got excessive center wear. Maybe because that's just not happening.
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Old 10-29-2008, 10:08 AM   #17 (permalink)
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Quote:
Originally Posted by tasdrouille View Post
This is sounding more and more like a myth. Every fuel economy enthusiast I know of who overinflated have seen increased tire life and even wear. There are a lot of people overinflating and reporting successful results. Yet, we don't hear about those who overinflated and got excessive center wear. Maybe because that's just not happening.
tasdrouelle: Well, yours is not exactly a scientific observation, so I'll offer one that's of equal value scientifically: I've been in the car business professionally since 1970, that's nearly 40 years now, and I have seen tire wear, belt separation and suspension problems due to overinflation many times. And I've seen tires that blew out due to it. Seen them first hand. It's happening!

Tires are a lot more complex than they appear. If you want an brainful, read the SAE book, "Tire Forensic Investigation" by Thomas R. Giapponi. You'll see the multitude of ways tires can fail... in gruesome detail. Call it CSI for tire guys ( : < )!

Yes, people get away with overinflation. That's partly because most tires are over-engineered. Plus, if you have to go one way or the other, overinflation is better in all areas than underinflation. So if a guy goes from checking his tires pressure every three years (whether they need it or not) and generally wearing out tires due being underinflated, then "getting religion" and going to the opposite extreme is going to seem like a whiz-bang concept that yield great results. If you compare tread life of a properly inflated tire vs an overinflated tire, you'll see some more unhappy numbers.

The over inflation saving graces for this Ecomodder group are that, a) they generally drive small, light cars, and b) those who know about such things buy tires with a high durometer and a tread design that offers low rolling resistance. These factors all contribute to a lower wear potential than the average tire (lower performance too, but...). Also, without wishing to insult anyone, logic dictates that a guy who destroys his tires by hyperinflation is not all that likely to advertise it in an, "I'm a bonehead," kinda post.

Me, I'm more concerned with the braking and handling issues. A little experimentation via a skidpad and stopping tests will show the loss of performance that comes from overinflated tires. The threshold is different for every tire/car combo and there may be a point where fuel economy and performance meet. Based on my knowledge, I'm willing to bet that point comes well under the tire's maximum pressure at any given load.

My little practical test showed the fuel economy difference between overinflated and properly inflated was too small to measure on my truck. Metro's rolling resistance test hints at much the same thing on his little car. To me, that makes the risk avoidance part of this very easy. If I discovered there was a 3 mpg gain in overinflating my tires, I'd crunch the numbers, do a little risk vs reward assessment and maybe give it a try. But, alas, all I got at 60 psi was a molar-loosening ride and squirrelly handling.
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My ultimate goal is not necessarily the highest mpg but to make my trucks more efficient configured as I need them.

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Old 10-29-2008, 10:36 AM   #18 (permalink)
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What Goodyear taught me

I was considered a tire expert in a former life. I got tours and info that others did not. Here are a few bits for you...

1) DOT tires are tested to caryy 15% more pressure and weight than is listed on the sidewall.

2) Heat is a huge enemy of tire wear. Over inflated tires run cooler than underinflated tires.

3) The first 32nds of tread wear occur more quicly than the last usable 32nds.
Think of a pencil eraser.

4)For best tire mileage, combining 1,2&3 Put new tires on the car in the late fall and max inflate them. The cooler temps and extra air will help the tire wear more slowly when it is most vulnerable, thus giving extended tire life.

5)Plastic valve caps are only dust covers and the shrader valve is only supposed to be a temporary seal. Use a metal cap with a seal for higher pressures. For best results, use a metal valve stem with a sealing cap.
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Old 10-29-2008, 11:00 AM   #19 (permalink)
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Quote:
Originally Posted by Denis View Post
Hey folks,

All this stuff with hyper inflated tires is fine but does it make economic sense ?

Overinflated tires will not last as long as normally inflated ones so while you save gas, you loose tire life ! Time for a reality check maybe
My response....
Prove it

I've got 20-25K miles on my tires inflated to 55 front, 50 rear.... Wear has been even, I still have more than half of my tread left.

Plus, I live in an area that gets a lot of heavy rain - having less hydroplaning risk has been a nice benefit

If you don't want to believe me (and all the others on this board with the same experience)... How about this?

And for thoroughness.... Stopping distance

Quote:
In general, these data suggest that the road surface and depth of water on the road have a large influence over stopping distance. Given a specific road condition, one can compare the difference in stopping distance when the tire inflation level is varied. The Goodyear test results imply that tire inflation can have a significant impact on stopping distance*, while the NHTSA testing implies these impacts would be minor or nonexistent on dry surfaces and wet surfaces with very little water depth.
Quote:
*# Stopping distance generally increases with lower tire pressure. The only exception was on concrete at 25 mph.

# With fairly deep water on the road, (0.050 inches is equivalent to 1 inch of rain in an hour) lowering inflation to 17 psi and increasing speed to 45 mph increases the potential for hydroplaning and much longer stopping distances.

# Except for 25 mph on macadam, the difference between 25 and 29 psi is relatively small.

FEA chapter III. tire pressure survey and test results

And that ends this reality check
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Old 10-29-2008, 11:09 AM   #20 (permalink)
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You people seriously need to stop quoting studies that compare Proper to Lower. 17 psi test results are completely irrelevent when discussing 35 vs 55.

I have raised my tires from 36/33 to 45/42. I notice longer coasts, rougher ride and DECREASED cornering and stopping ability on dry pavement. I race my car (on race tracks, not strips or ovals), so i can communicate with my tires well. I won't lower my pressures due to this decrease in grip, but that's only because I am a HIGHLY attentive driver compared to the masses, and I have high speed vehicle control training. If you think you know what you are doing, remember that 80% of drivers feel that they are better than 80% of drivers!

If you drive like a granny ALL the time and you stay well back from people in adverse conditions no matter how late you are, feel free to bump them up over 50. All others are in blissful ignorance land.

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