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Brian Voelker
08-06-2008, 07:21 AM
All the hype on over inflating tires got me wondering if was actually tested to standards or just fly by seat of pants reporting. My big misgiving other than safety is that if you have a larger in diameter tire the odometer reads less miles and the speed on odometer reads slower. Someone give Kathy a call and get Bill off the tuners and on to testing this!
BV

tylerw02
08-06-2008, 12:52 PM
We know that inflating tires can reduce fuel cost. It does this by
putting less surface area on the ground and making the tire more
buoyant. So there is a smaller surface and reduced friction. The
smaller surface area must therefore absorb more heat. Heat makes
tires wear faster. There is a slight increase in circumference,
changing the gear ratio and increasing mechanical advantage, but
not enough to matter. The center of the tread will wear off prematurely
as a result of over-inflation.

Tires are made with petroleum. They are shipped with it. If we
over-inflate them, they wear out faster. We have to dispose of the
worn tires and purchase (and manufacture) new ones. What is the
environmental impact of the increased tire demand? How much more oil
will this tire replacement cost?

vinny
08-06-2008, 01:14 PM
Much like the lack on insight in going to ethanol. Did all the brains in Washington consider the effect on food prices when they decided to use corn for fuel? It must be me, it can't possibly be all of them.
vinny

Fred J
08-06-2008, 01:54 PM
Proper inflation will save you more in tire wear and vehicle maintenance costs, than over inflation will will save. Over inflation is not only costly, but dangerous. Of course if you follow this myth, be sure you have a good health/accident or burial policy.

gt40
08-06-2008, 07:31 PM
Lets say that the manufacture recommends 35 psi maximum in your tires. You plan on going on a trip so in the morning when the air is cool in your tires you check them and the psi has dropped 5 psi. You inflate your tires to 40 psi which is only 5 psi over what is recomended. Then you pack up your car with your wife and 3 little childern and start out on your vacation.

Now after driving 4 hours and the outside temperature increases to over 90 degrees and the heated air in your tires increase to 50 psi and your left rear tire has a blowout and you lose control and your car goes down into a ditch and rolls over.

DUH???

"Aim small miss small", :D

gt40

Bill Wynne
08-06-2008, 08:03 PM
Air expands due to temperature at the rate of 1/496 th. of its volume per degree fahrenheit and that is a law (scientific). That is based on absolute zero being -459 degrees and freezing being 32 degrees Fahrenheit. Assuming that the air in your tires are in a confined space, which it isn't, you can see why the pressure increases as much as it does.

There now, I have contributed to your body of knowledge.:) Go figure.

Concho Bill

jwa
08-06-2008, 08:16 PM
Now after driving 4 hours and the outside temperature increases to over 90 degrees and the heated air in your tires increase to 50 psi and your left rear tire has a blowout and you lose control and your car goes down into a ditch and rolls over.

DUH???

"Aim small miss small",

gt40

You have just helped to lower the demand for gas, wasn't that the point?:D
Jerry

alinwa
08-06-2008, 08:40 PM
Good Ol' Genocide Jerry in for a point.... ka'TCHING!! :D


LOL


al

Fred J
08-06-2008, 09:08 PM
In Texas, the road temperature can reach as high as 150 degrees on a hot sunny summer afternoon. Often when traveling home from a match, we will witness blowouts and thread separation at an alarming rate. Some time there are fatalities and other times just a costly accident. I also caution my wife, not to follow too close during these hot conditions.

Paul Fielder
08-06-2008, 09:14 PM
I'm ignorant on this subject!!

pf

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Yote
08-06-2008, 09:36 PM
Paul, all the years I was with Ryder, tire maintenance cost was higher than any other cost. To keep it as low as possible, we were forced to come up with several different strategies to keep air psi at the correct level. Not over inflated and certainly not underinflated. Either way causes running costs to go up.

As stated earlier, with more psi in a tire, the less contact the tire has with the road. This will equal maybe a tad bit better mileage. It also causes the tire to run hotter and wear quicker in the middle of the tires footprint. Not to mention since less rubber is touching the road, you have less traction which equals hydroplaning in wet conditions.

I do not recommend running tires overinflated. You WILL spend more because your cost per mile per tire will go up. In the long run, you will lose money, if not much more.

Paul Fielder
08-06-2008, 09:44 PM
Paul, all the years I was with Ryder, tire maintenance cost was higher than any other cost. To keep it as low as possible, we were forced to come up with several different strategies to keep air psi at the correct level. Not over inflated and certainly not underinflated. Either way causes running costs to go up.

As stated earlier, with more psi in a tire, the less contact the tire has with the road. This will equal maybe a tad bit better mileage. It also causes the tire to run hotter and wear quicker in the middle of the tires footprint. Not to mention since less rubber is touching the road, you have less traction which equals hydroplaning in wet conditions.

I do not recommend running tires overinflated. You WILL spend more because your cost per mile per tire will go up. In the long run, you will lose money, if not much more.

...I am relieved!!

I watched the news the other night and was told I was ignorant for not watching my tire pressure??

All this time I thought it was my blood pressure I should consider!!

pf

<><

Dennis Sorensen
08-06-2008, 10:23 PM
At highway speeds you will blow an under inflated tire up much quicker than an over inflated tire... it flexes too much and heats up way to much and fails due to the flexing and heat buildup. Over inflated will give poorer traction but it will not heat up that much... over inflation does not cause heat buildup. It will run cooler if anything.

Slightly over is much better than slightly under in my opinion... driving for 53 years now... never blown a over pressured tire...

Paul Fielder
08-07-2008, 08:54 AM
....of sandy country by taking air out of the tires. Pretty good trick but you need to do it as soon as you notice you are spinning and not get the tires to deep. gives them more bite.

I usually run my pressure in the middle to the upper 'window' of whatever the tire mfg recommends.

Hitting a bad pot-hole with over or under inflated tires hurts!!

pf

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Roger T
08-07-2008, 09:01 AM
All the hype on over inflating tires got me wondering if was actually tested to standards or just fly by seat of pants reporting. My big misgiving other than safety is that if you have a larger in diameter tire the odometer reads less miles and the speed on odometer reads slower. Someone give Kathy a call and get Bill off the tuners and on to testing this!
BV

Run the Tallest/ Narrowest tire the you can. The odometer gear can be changed out at any good Transmission shop to compensate for tire height. stay at/within manufacterers specs (liability). Cut hole in floor pan for Fred Flintstone stops an starts :rolleyes:,and your on your way to gas independence....... BTW save the old wornout tires cut'em up to RESOLE your Flinstone BRAKE PADS:D

Wilbur
08-07-2008, 11:52 AM
We would cut the "bead" off of a tire and stretch it over a tire that would still hold air. A poor man's retread if you will. It wasn't an easy thing to do with screwdrivers and jack levers by no means but necessary at the time.

Paul Fielder
08-07-2008, 03:04 PM
We would cut the "bead" off of a tire and stretch it over a tire that would still hold air. A poor man's retread if you will. It wasn't an easy thing to do with screwdrivers and jack levers by no means but necessary at the time.

...how a retread would stay on, much less what you are describing?? Tires (in general) are pretty darn tough.

My Tahoe needs some new rubber and it is one of those items I hate buying.

pf

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HovisKM
08-07-2008, 03:30 PM
We would cut the "bead" off of a tire and stretch it over a tire that would still hold air. A poor man's retread if you will. It wasn't an easy thing to do with screwdrivers and jack levers by no means but necessary at the time.

And don't forget how fast you had to hurray before the owner got back....:D:D

Hovis

Yote
08-07-2008, 03:34 PM
Paul, if I'm not mistaken caps are cooked on from a vulcanizing/heating process. Problem is sometimes these caps come or sling off. Big drama on the hiway when this happens on a semi. That's why I give them a wide berth on the road. I pass them as quickly as possible cause you never know when one will let go. I've seen slung caps beat the crap out of the bottom of trailer floor frames and bend heavy angle iron mudflap brackets into pretzels. We always ran caps on trailers and drive axles of trucks. I always hated them cause they sure caused alot of problems, especially at 3:00am and on weekends.

adamsgt
08-07-2008, 03:56 PM
When I bought my last set of tires from Costco, they used nitrogen to inflate them. The service manager told me that because nitrogen was an inert gas the tires would not heat up or lose pressure like a tire filled with air. Anyone out there confirm or refute these claims?

Dennis Sorensen
08-07-2008, 04:30 PM
When I bought my last set of tires from Costco, they used nitrogen to inflate them. The service manager told me that because nitrogen was an inert gas the tires would not heat up or lose pressure like a tire filled with air. Anyone out there confirm or refute these claims?

All sorts of claims on nitrogen but I think it may retain pressure better because of the larger size of the molecules compared to air...

A tire will not heat excessively unless the pressure is too low or the load excessive... it is the excessive flexing of the tire that causes heat buildup.

cdupuy
08-07-2008, 05:01 PM
And some more things to worry about
Newer Vehicles with the Tire Monitor will NOT allow higher pressure (installed)unless you want to look at the dash light for ever! this also applies to the underinflated tire as well, as it will bring on the dash light.
See the wide or big tires that are put on most trucks, those are killers of fuel mileage, also REMEMBER when you change tire size you MUST re-flash the onboard computer to include the different diameter or your Speedo WILL be off AND the engine performance will be somwhat degridated.
Ya want better mileage??? buy less cylinders, and the Manual transmissions.

OBAMA is FULL of IT.
OH and did I say that overinflated tires WILL shake the vehicle to death, along with going to heavier ply/load rating, YEP

Clarence

Bill Wynne
08-07-2008, 05:11 PM
When I bought my last set of tires from Costco, they used nitrogen to inflate them. The service manager told me that because nitrogen was an inert gas the tires would not heat up or lose pressure like a tire filled with air. Anyone out there confirm or refute these claims?

The claims about nitrogen not heating up and expanding are bogus. Why not put helium in you tires?

Gas expands due to temperature at the rate of 1/496 th. of its volume per degree fahrenheit and that is a law (scientific). That is based on absolute zero being -459 degrees and freezing being 32 degrees Fahrenheit. Assuming that the gas in your tires are in a confined space, which it isn't, you can see why the pressure increases as much as it does.

I was told by my tire installer that the inert nitrogen gas in the tires would cause the tires to last longer. He just laughed when I asked him what the air on the outside of the tires would do.

There must be an advantage to use Nitrogen in your tires. I paid $25 for them to put in in mine. When the tires heat up the pressure still increases. Go figure.

Concho Bill

John Kielly
08-07-2008, 05:41 PM
There must be an advantage to use Nitrogen in your tires. I paid $25 for them to put in in mine.
Well, you made somebody's life just that little bit more comfortable. :rolleyes:

Thinking of our main interest & the use of nitrogen there, maybe there's some advantage to having a dry gas in the tyre. What is the coefficient of expansion of water when it converts to steam?

Greg Culpepper
08-07-2008, 06:36 PM
John,

The water inside a tire is already vapor (steam) so there is no state change that would alter the ideal gas law. Tires with liquid water inside are hard to balance and work best on tractors. Besides, very few tires will reach 212 degrees on the street unless they are very under inflated. Tires usually die from heat as a result of under inflation.

Greg

Mr. D
08-08-2008, 03:15 AM
If you are serious and not into cars:

Tire pressure should be determined by the shape of the tire as it meets the road. Pressures printed on the sidewalls are maximums affected by lawyers to avoid law suits. It is like loading a 38 Special to market. A lawyer will tell you to load it based on legal suits rather than the specific gun and the pressure it will handle. Example: If you have a pickup with a heavy, big block engine and a 4x4 front axle it will need more air pressure in the front tires than the rear tires with that empty pickup bed. There should be just a slight bulge where the rubber meets the road when you have the right inflation. Under inflated tires will heat up and also wear the outside tread, while over inflated will burn out the centers and ride hard. If your tires get hot to the hand on an average day they may be under inflated. I inflate tires based on how they look as they meet the road, how the vehicle handles and the heat produced on the highway rather than the maximum the tire guy has to put in them by law. It is like loading a 38 Special. A lawyer will tell you to load it based on legal suits rather than the specific gun and the pressure it will handle.

Every time you apply the brakes you have wasted fuel used to move the vehicle! Time the lights with your speed so you avoid braking and drive at an even speed. Drive at speeds where wind resistance is minimized (60 rather that 80 MPH) when possible :eek:, and in away that you brake the very least for lights, traffic, etc. Jack rabbit starts that have you braking for the next light are for teenagers where Dad is paying for the fuel.

Keep your car tuned!

On small engines don't use the AC under 45 MPH if not needed, open a window. Over 45 MPH. the AC will use less fuel than the drag of open windows.

tylerw02
08-08-2008, 03:13 PM
At highway speeds you will blow an under inflated tire up much quicker than an over inflated tire... it flexes too much and heats up way to much and fails due to the flexing and heat buildup. Over inflated will give poorer traction but it will not heat up that much... over inflation does not cause heat buildup. It will run cooler if anything.

Slightly over is much better than slightly under in my opinion... driving for 53 years now... never blown a over pressured tire...

I don't think anybody is suggesting under inflating tires, rather over inflating them. I've blown over-inflated tires.

tylerw02
08-08-2008, 03:16 PM
Mr D, I've noticed, like nodes when loading, my truck has certain speeds where it gets the best fuel mileage. It does best at 58 mph, then does progressively worse until it finally picks back up at 75 mph. It gets about 17 mpg at 75, and 15 at 70. Last time I checked, it was getting 19 at 58 mph.

WillAdams
08-08-2008, 04:02 PM
Nitrogen in the tires !! Darn, here I was thinking that if I used helium I would get better mileage since it is a lighter gas!!! Good thing the balloon company was closed otherwise I would have wasted my money.

Mr. D
08-08-2008, 06:10 PM
Mr D, I've noticed, like nodes when loading, my truck has certain speeds where it gets the best fuel mileage. It does best at 58 mph, then does progressively worse until it finally picks back up at 75 mph. It gets about 17 mpg at 75, and 15 at 70. Last time I checked, it was getting 19 at 58 mph.

Likely a combination of wind resistance and hitting the RPM power curve just right where you are producing the most H.P. for the least fuel.

speedpro
08-09-2008, 02:42 AM
If we listen to and get in-tune with our mechanical drive componets and pay attention to the reaction and feel of our steering and suspension componets, in essense become one with our machines we will always maximize their efficency.

I'll never understand how some of the fellas in the machine shops I've worked in would'nt change out a tool until the machine crashed and burned :eek: not to mention all the "out of spec parts" that were produced prior to failure. :mad:One can tell in an audiable sense the sound of a dull tool as it tears the work as opposed to actual machined cuts. What's more amazing is that they keep their job's :eek: :confused:

I'm deaf as h*ll, and old to boot, yet my machines, gun's and songbird's talk to me and I hear them just fine, it's those "other" voices I keep hearing that concern me! :confused:

RayfromTX
08-09-2008, 07:30 AM
This thread has the largest collection of old wives' tales that I've seen lately. This is a subject that tends to bring out the unfounded opinions stated as fact more than usual.

Nitrogen makes up 78% of our atmosphere. Do you really think that replacing some of the oxygen in your tires with nitrogen is going to have any affect at all? They don't change your tire in a pure nitrogen atmosphere. You will always have a significant amount of oxygen in your tires unless you drain and refill them with nitrogen many times.

Many auto manufacturers recommend a lower pressure than the maximum shown on the sidewall. I can guess this is for a softer ride but have no real knowledge. The maximum pressure is a crapshoot that is arrived at to cover any vehicle in any climate at any load up to max on any roads. Stating that inflating tires over max by some amount is a death wish of some sort is presumptuous. Under-inflation is a much more dangerous situation in almost every instance. The tires on my Prius have a stated max pressure of 44 psi. The manufacturer says to fill them to 35 in the front and 33 in the rear. I use 42 and 40 which has shown to increase my mileage by 5 mpg countless times. If the dealer changes my pressure to the recommended while I'm in for my free oil change, I can tell in just a few miles because my mileage readout starts to drop for no apparent reason. My lifetime average in the Prius is in the mid 50s over 104,000 miles.

Testing in many vehicles has shown that the wind resistance caused by rolling down the windows uses substantially less energy than running the air conditioning. I have proven this to myself on my car. A bogus statement was made back in the energy crisis of the 70s and it has been quoted as fact many times ever since.

Wind resistance at 70 mph is double that of the wind resistance at 50 mph. The energy required to overcome the increased resistance is four times that of the lower resistance. Wind resistance is only a part of the resistance puzzle, which includes rolling resistance and pumping resistance and other frictions within the drive train. To save gas, slow down.

I could go on but I just realized that I'm again trying to inject facts and accuracy into a discussion that has a larger goal of killing time while shooting the breeze with friends. It is one of my many character defects. To those I may have ticked off, I apologize.

tylerw02
08-11-2008, 11:38 AM
Likely a combination of wind resistance and hitting the RPM power curve just right where you are producing the most H.P. for the least fuel.

Basically my assumption.

tylerw02
08-11-2008, 11:40 AM
Wind resistance at 70 mph is double that of the wind resistance at 50 mph. The energy required to overcome the increased resistance is four times that of the lower resistance. Wind resistance is only a part of the resistance puzzle, which includes rolling resistance and pumping resistance and other frictions within the drive train. To save gas, slow down.


Odd....my truck doesn't get the best mileage at slower speeds. Simply because we have a thing called gears.

BUSHMASTER1
08-11-2008, 01:11 PM
I own an idependent Lexus repair shop. Nitrogen in tires main benefit would be larger molecules = slower tire pressure decrease due to natural permeation due to porosity of rubber. Our regular customers come in at 5,000 mile intervals. Tires with air lose about 3-4 psi in this amount of time. Nitrogen is averaging 3-4 psi in the same interval. As far as I'm concerned it's a gimmick. I certainly wouldn't buy a $5000.00 nitrogen machine to make it back $25.00 at a time. I hope they're really putting nitrogen in your tires if you're paying for it!

Bill Wynne
08-11-2008, 07:45 PM
Bushmaster,

I really don't know, but don't they just purchase a bottle of nitrogen and put it in tires? And I too am pretty sure that it is a gimmick.

Concho Bill

BUSHMASTER1
08-12-2008, 07:14 AM
No Bill, it's a nitrogen generator, $4500-$5000. Looks like a freon recovery machine but green.

Mr. D
08-12-2008, 11:18 PM
What's wrong with you guys? Get a one cylinder diesel pickup like me and stop wasting fuel: :D


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