quote Originally posted by theogre: No and Doesn't matter here. Photoshop poor pictures to read tire data... No thanks. Speed rating affect wear warranty as I listed above from Continental's ContiProContact Warranty.PDF page 7 and from Tirerack. 205 is available in T & H and Both can have same tread compound etc but have different wear warranties because of speed rating. Saying High Tire Pressure = Long Life? No... In general, Long wear warranties means harder tread compound. Getting 100,000+ miles on hard compound tires is not very hard.

Speed rating affects treadwear warranty but the UTQG (Uniform Tire Quality Grade) affects treadwear itself.

http://continentaltire.cust...wers/detail/a_id/461

quote Treadwear The treadwear grade is a comparative rating based on the wear rate of the tire when tested under controlled conditions on a specified government test track. A tire graded 200 would wear twice as long on the government test course under specified test conditions as one graded 100. It is wrong to link treadwear grades with your projected tire mileage. The relative performance of tires depends upon the actual conditions of their use and may vary due to driving habits, service practices, differences in road characteristics and climate.

http://www.americastire.com/dtcs/infoTreadwear.dos

quote The treadwear grade is a comparative rating based on the wear of a tire when tested carefully under controlled conditions. For example the useful tread on a tire graded 400 should last twice as long as a tire graded 200. However, another tire manufacturer may grade a comparable design 300, so a grade of 150 would last just half as long under their grading scheme. The lesson learned is to not use one manufacturer's grade versus the other, but instead to compare tire grades within a given brand. Actual treadwear performance can vary tremendously according to the tire's real-world use. Variations in driving habits, service practices (most importantly air pressure maintenance), road conditions and climate affect tire life.

Under the exact same conditions, a 205/60/R16 92H Continental ContiProContact tire with a treadwear grade of 400 will yield roughly the same mileage as a 205/60/R16 91T Continental ContiProContact tire with a treadwear grade of 400. The difference in speed rating will not cause a 20k mile difference.

quote Originally posted by edfiero: Cant wait to see the date code on those tires.

I have a feeling we'll be waiting a while.

quote Originally posted by kendallville: I have looked for this date code on my tires , but cant find one . do all tires have them ? or only new tires ? or may be they started in a certain year and older tires don't have them. did'nt mean to change the subject but if I wait to ask I'll never remember

Actually, I think we're already a little off topic from the OP.

quote Originally posted by kendallville: 186 then what looks like a circle with a - inside the web site says a triangle for tires made in the 90s maybe they are the original tires? edit to add I have allways ran 40psi any thing less and the rear end wants to wander.

The circle with the line through it is rubber molding around the flat head screw holding the plate of the production code to the tire mold. In the picture Marvin posted above yours, phillips style screws were used.

quote Originally posted by Marvin McInnis: Date code could even be 1986. Regardless, that tire should be replaced due to the extensive sidewall checking alone; failure is only a matter of time.

I second that notion. It's suggested to take any tire of ten years of age or older out of service, regardless of remaining tread life and external appearance.

Front 225/40/18 36psi
Rear 265/35/18 44psi
I am replacing the tires now after 7 years of use. This is the same tire pressure a lot of Porsche's use.

On my beater car, 95 Geo Metro. I have been running 50 psi for the past 6 years.

quote Originally posted by tampalinc: On my beater car, 95 Geo Metro. I have been running 50 psi for the past 6 years.

You do realize that if you're ever in an accident especially if there are injuries involved, that if accident investigators find you have intentionally over-inflated your tires beyond the manufacturer's maximum allowable pressure (45 psi in most cases) that you could be found liable and that your insurance company could deny you coverage after the fact. If the sidewalls of your Metro's tires state the maximum pressure to be less than 50 psi, your admission here would be good as gold to the insurance company as well as any to anyone suing you. (I'll erase the fact that I've quoted you if I see that you change your mind and erase erase your original post.)

Just curious, under what pretext did you decide that 50 psi was a good idea?

quote Originally posted by Bloozberry: You do realize that if you're ever in an accident especially if there are injuries involved, that if accident investigators find you have intentionally over-inflated your tires beyond the manufacturer's maximum allowable pressure (45 psi in most cases) that you could be found liable and that your insurance company could deny you coverage after the fact. If the sidewalls of your Metro's tires state the maximum pressure to be less than 50 psi, your admission here would be good as gold to the insurance company as well as any to anyone suing you. (I'll erase the fact that I've quoted you if I see that you change your mind and erase erase your original post.) Just curious, under what pretext did you decide that 50 psi was a good idea?

I am still under the Max PSI on the sidewall of the tire, which is 51 PSI.
Some good reading if you have time. http://www.cleanmpg.com/for...light=tire+pressures

I have found over the years ( with my daily drivers) that if I run more than 8 pounds over what the owners manual cold tire pressue says, the center portion of my tires will always wear out first.

I get the best combination of wear, ride and comfort by adding about 3-4 pounds over the recommended cold tire pressure (the sticker inside the door)

quote Originally posted by tampalinc: I am still under the Max PSI on the sidewall of the tire, which is 51 PSI. Some good reading if you have time. http://www.cleanmpg.com/for...light=tire+pressures

Quoted from your source: "50 + #’s on a MAX Sidewall rated tire leads to even higher FE. Pros, higher FE, less tread wear, more even tread wear across the treads width, shorter braking distances in a variety of conditions, and in many cases, even better handling. Cons, higher NVH (Noise, Vibration, Harshness)."

Running the maximum pressure will reduce rolling resistance, true, because by doing so you make the tire contact patch smaller and the sidewall stiffer. But you cannot simultaneously have reduced road friction and "shorter braking distances". Nor can you have "more even tread wear" by lessening the contact of the tread on the outer and inner edges of the the tread.

Further, stating that you get less tread wear may be true, but in a warped sense because the tire will only wear where it's loaded the most: in the center. I suppose if only a third of your tire is worn out because the two sides are still like new, then you achieve less tread wear.

Then there's the statement about better handling. To the average driver a stiffer sidewall only "feels" like better handling because there's less lean in a corner. Unfortunately less "lean" does not characterize better handling. Suspensions are designed to maintain the largest possible tire contact patch as the body rolls into a corner by attempting to keep the tire perpendicular to the road. If you arbitrarily choose to overinflate your tires to the extreme to reduce the tire contact patch under all circumstances, then that's at odds with improving actual road holding ability in any sense whether it's braking, accelerating, or rounding corners.

It's a free world though so believe what you want.

For future reference, I came across the following standard formula recommended by the tire industry standards organizations ... ETRTO in Europe and RTA in North America ... to calculate proper tire inflation pressure :

P = P_r (((L - L_c) / (L_r - L_c)) ^ (1 / X))

Where:

P = recommended tire pressure for actual load
P_r = rated (usually maximum) tire pressure ... from the tire sidewall or published specs
L = actual tire load (can use actual axle load / 2 ... or actual vehicle weight / 4)
L_c = tire "construction" load ... the load that the tire itself will support at normal deflection when uninflated ... 0 to 100 pounds
L_r = rated (usually maximum) tire load ... from the tire sidewall or published specs
[
X = empirical power factor ... 0.8 (European standards), 0.7 to 0.8 (North American standards since 2006)

N.B. The symbol ^ indicates exponentiation (i.e. "to the power of")

N.B. It is not clear whether P and P_r are gauge pressure or absolute pressure. More research is indicated.

N.B. Instead of using the tire's rated maximum for P_r and L_r, for OEM tires you can use the car manufacturer's recommended pressure and axle loads (divided by 2) as placarded on the individual vehicle. The calculated pressures using either method should be close.


Notes on construction load (L_c) and power factor (X):

L_c = 0, X = 0.585 ... introduced in 1928 for bias-ply tires
L_c = 0, X = 0.500 ... used in North America for passenger car tires down to 50% aspect ratio until 2006
L_c = 0, X = 0.650 ... used in North America for passenger car tires lower than 50% aspect ratio until 2006
L_c = 0, X = 0.700 ... used in North America for passenger car tires since 2006
L_c = 0, X = 0.800 ... used in Europe for decades; also used in North America for passenger car tires since 2006


Source


Edit: Running a few validation checks, this formula seems to give pressures much lower than expected. More research is indicated.

[This message has been edited by Marvin McInnis (edited 04-30-2013).]

By the way, the treadwear on that Sebring is NOT even. Look at the sipes on the very outer edge. They are deeper than the middle.

Having sold and installed hundreds of tires, 90% of them were replaced from under or over inflation- most over. Its easy to tell when there is no air in the tire. The tread will visibly cup.

I almost always inflated tires to 35 psi. 95% of factory recommendations are between 32 psi and 36psi.

How dry cracked can a tire be and still be safe?

quote Originally posted by Marvin McInnis: Close ... but not quite correct. See below.

Thanks. my math isn't good since my stroke...

I don't know who came up w/ 1PSI per 10°F... (Degree symbol, See Special Characters (Webmonkey). Just type &code; w/o [ ] ♥ )
Likely they rounded to nearest Integer because many gauges just won't read small numbers, cheap gauge are often have errors, etc.
And many can remember 1PSI per 10°F

"They" also said 1psi per month from leakage even w/ best tires and rims but Alloy rims a famous for leaking air... Example I have 1 old OE rim that leaks 3-5 PSI every week or two. (I know problem is the rim because even w/ new tire etc still have same leak rate.)

quote Originally posted by Marvin McInnis: Date code could even be 1986. Regardless, that tire should be replaced due to the extensive sidewall checking alone; failure is only a matter of time.

Yes, anything w/ 3 digit date code should be junked. At minimum best, tire is 17 years old and counting.
Even NOS tires can have problem... Rubber can rot because Ozone eats Rubber sitting on a self.

quote Originally posted by 2.5: How dry cracked can a tire be and still be safe?

Well, ideally no dry rot is best, but most tires are dry rotted at least a little. If you park your car outside, the sunlight is what causes most dry rot (which is why a lot of spares have covers and rv's cover their wheels ect). So just about any tire that is at least a few years old will have some cracking. It becomes a problem when the inner layers crack too. If the cracks leak air, or you can flake the rubber with your hands or flex the tires and see the belts they need to be replaced. Also any tire over 5 or 6 years should probably be replaced too, for good measure. Dry tires are brittle tires so use your own judgement.

Lots of little cracks aren't a huge deal (but start saving for a new one in a few months), but few large cracks is no good (which is what happens the longer it goes without replacing).

quote Originally posted by theogre: I don't know who came up w/ 1PSI per 10°F...

1 PSI per 10°C would be really close. Maybe that's where it came from. (I realize that mixing PSI [English units] and degrees C [SI/Metric units] in the same formula is probably a bad idea. Too bad Americans have so much trouble with the SI/Metric system.)

Correction (using absolute rather than gauge pressures): More correct values are ~1.5 PSI per 10°C and ~0.85 PSI per 10°F.

quote See Special Characters

Thanks for the handy reference.

[This message has been edited by Marvin McInnis (edited 04-30-2013).]

Tip, if you want to calculate more accurate tire load, use a set of wheel scales (one scale under each wheel/tire), with the tires set at the MAX pressure on the side wall. Measure the left two tires while sitting in the driver seat, and the right two while sitting in the passenger seat (to allow for increased weight of carrying a passenger). This will give you a better number, as the Car isn't balanced 50/50 front to rear, or necessarily side to side.

Simply dividing the gross vehicle weight by 4 will likely end up with slightly overinflated tires in the front, and slightly under-inflated in the rear. For most, the values will probably be Close Enough(TM).

quote Originally posted by Bloozberry:But you cannot simultaneously have reduced road friction and "shorter braking distances". Nor can you have "more even tread wear" by lessening the contact of the tread on the outer and inner edges of the the tread. Then there's the statement about better handling. To the average driver a stiffer sidewall only "feels" like better handling because there's less lean in a corner. Unfortunately less "lean" does not characterize better handling. Suspensions are designed to maintain the largest possible tire contact patch as the body rolls into a corner by attempting to keep the tire perpendicular to the road. If you arbitrarily choose to overinflate your tires to the extreme to reduce the tire contact patch under all circumstances, then that's at odds with improving actual road holding ability in any sense whether it's braking, accelerating, or rounding corners. It's a free world though so believe what you want.

I'm not sure I agree. Autocrossers are known to run pressures that are way high in the front, and only slightly high (or even low) in the rear. The result is better grip, better handling, and less oversteer (due to the low rear pressure). Autocross is a great tire laboratory, and it shows increased grip with higher pressures. I always thought that the tradeoff would be excessive wear in the center, so I've always run my tires at the factory specs.

quote Originally posted by dobey: Simply dividing the gross vehicle weight by 4 will likely end up with slightly overinflated tires in the front, and slightly under-inflated in the rear. For most, the values will probably be Close Enough(TM).

Using the F/R axle weights placarded on the car will allow you to get you even closer. For example, the door placard on my Formula lists a GVW of 3227 pounds, max 1295 pounds front axle and max 1932 pounds rear axle. Of course, those numbers are for a fully loaded vehicle: full fuel, 2 passengers, and maximum allowable baggage.

When you can do it, individual wheel weights are best ... but even those only represent a one-time snapshot for a specific vehicle loading. If there is an autocross being held nearby, the organizers will often be willing to weigh your car for a small donation when the scales are not in use for competitors.

quote Originally posted by Marvin McInnis: When you can do it, individual wheel weights are best ... but even those only represent a one-time snapshot for a specific vehicle loading. If there is an autocross being held nearby, the organizers will often be willing to weigh your car for a small donation when the scales are not in use for competitors.

Indeed. Also why I said to sit in both seats when doing it (for most people, for some it won't matter). Any single weight reading will just be a snapshot. But one should try to weight their car in conditions as close to typical as possible. 1/2-3/4 tank will give a closer to average fuel weight, depending on how low you let the gauge get before filling up. A little over there is better, as it's not an insignificant amount of weight, and will shift during driving/braking, so the load won't remain even at all times, particularly if you spend more time in stop-and-go traffic, rather than all highway. If you have a sunroof car, and mostly only drive in sunny weather with the glass out, weigh the car with the glass stored up front under the hood. If you typically have a passenger, weigh the car with your passenger sitting in it, and you in the driver seat, or use some dead weight that's within a couple pounds of actual weights (sacks of potatoes work pretty well for this). If you don't typically have a passenger, weigh without one.

If you're going to weigh your car for the purpose of getting the tire pressure right, might as well get as close to actual conditions as possible.

Here's a good example of what happens to over-inflated tires. I just took a Pontiac Solstice out of storage for a customer and went to top up his tires as part of several services I perform. After a full 6 months of storage, his tires were all at either 34 or 35 psi. I assume that his tires lost approximately 2-3 psi over the winter, but let's say they didn't lose anything for argument's sake:



The stock tires are P245/45/18.



The GM recommended tire pressure for all four corners is 29 psi:



That means he's been running at least 5 psi higher than recommended, but more likely in the neighborhood of 8 psi higher. Here's what all four tires look like up close. Notice the sipes are completely worn off the center of the tire and are progressively less worn towards both outer edges. If that is not an indication of a steel belted radial tire that has been ballooning in the middle due to over-inflation, then nothing will convince you.



Here's a shallower angle photo of the treads... you'll notice that the tread wear indicators (the little raised lines running across the tire between the tread blocks) are still about 3/32" from being level with the outer tread blocks, but are worn down to the blocks in the center of the tire. What's deceiving is that there is more than just 3/32" difference between the depth of the tread at the outside and middle of the tire.

Perfect example Blooz. Bottom line, the manufacturers who spend millions to find ideal tire pressure for each vehicle KNOWS WHAT THEY ARE TALKING ABOUT.

quote Originally posted by BlackEmrald: Perfect example Blooz. Bottom line, the manufacturers who spend millions to find ideal tire pressure for each vehicle KNOWS WHAT THEY ARE TALKING ABOUT.

I think you grossly overestimate how much manufacturers spend on that. It's simple math. There's no need to spend millions of dollars to find the recommended tire pressure for each vehicle. Build a car, weigh it, do the math based on the tires it will be equipped with at sale, and then build a million more with a sticker that says the same thing. It costs more to print the sticker on the door, than they spent to do the math.

quote Originally posted by Marvin McInnis: Maybe. A 10% increase in pressure would require a temperature rise of ~53 degrees F, which is pretty high under normal driving conditions.

Wouldn't it depend on your beginning pressure as to how much additional heat would need to be applied to increase pressure by 10%?

For instance, if you start with 30psi, an additional 10% would be an additional 3psi.
If you start with 40psi, an additional 10% would be an additional 4psi.

The size of the rim and tire are basically constant ( I know the tire will be nominally larger if inflated more, etc) so the total area in square inches will be the same. I have no idea of the area of the inner surface of of a tire would be in square inches but lets guess it is 500 square inches. For the tire starting out at 30psi, the pressure would have to increase by 1500 pounds or 3psi.

For the tire starting at 40psi, the pressure would have to increase by 2000 pounds or 4psi.

I would not think that these two examples would require the same amount of added heat.

Or am I looking at it wrong?

------------------
Jonathan

Please join me in prayer that forum member Wichita gives his life to the Lord Jesus.
https://www.fiero.nl/forum/Forum6/HTML/100383.html
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Well first off, I was gone ferrying my plane down to the island. Im not going to bother crawling under my car looking for numbers. You turds would just find a reason to say theyre photoshopped or faked anyway. I run 40+ pnds in all my cars and it works fine for me. I really dont give a crap if you do or not. I laugh when my tires last double or tripple what you get running the awesome factory recommendations. Your the same birdbrains who change oil every 3000 miles....EVEN when the MANUFACTURER SAYS 7500 in most cases. So much for doing what the all knowing manufacturers say. Dont that make you hypocrites ? I DONT do anything a manufacturer recommends...I do what works for ME. Do whatever you want.

quote Originally posted by Boostdreamer: Wouldn't it depend on your beginning pressure as to how much additional heat would need to be applied to increase pressure by 10%?

No. You also need to substitute "temperature rise" for "additional heat" in your statement. You can measure (and feel) tempertaure directly, but not heat; they are two related but different thermodynamic properties.

quote For instance, if you start with 30psi, an additional 10% would be an additional 3psi. If you start with 40psi, an additional 10% would be an additional 4psi.

A 10% change in absolute temperature of the air in a tire will result in a corresponding 10% change in its absolute pressure.
To repeat, we're talking about 10% increase in absolute temperature, and we're taking about change in absolute pressure rather than gauge pressure. So if you start with 30 psig (45 psia), the pressure rise for a 10% rise in absolute temperature would be ~4.5 psi; for an initial 40 psig (55 psia) the rise would be ~5.5 psi.

quote The size of the rim and tire are basically constant ( I know the tire will be nominally larger if inflated more, etc) so the total area in square inches will be the same. I have no idea of the area of the inner surface of of a tire would be in square inches but lets guess it is 500 square inches. For the tire starting out at 30psi, the pressure would have to increase by 1500 pounds or 3psi. For the tire starting at 40psi, the pressure would have to increase by 2000 pounds or 4psi. I would not think that these two examples would require the same amount of added heat. Or am I looking at it wrong?

You're looking at it wrong. First, it doesn't matter what size the tire is when you're talking about temperature and pressure. You also appear to be mixing percentage difference in temperature with pressure change in fixed units. You need to think "percentage in" and "percentage out," and only then can you convert back to psi or kPa. You also need to be using absolute temperature and pressure. Finally, we're talking about temperature here, not heat; you can't directly measure the amount of heat you're putting into a tire.

[This message has been edited by Marvin McInnis (edited 04-30-2013).]

Is it just me or does it seem a bit ridiculous to have 61 posts about recommended tire pressures? Jeez

quote Originally posted by dobey: I think you grossly overestimate how much manufacturers spend on that. It's simple math. There's no need to spend millions of dollars to find the recommended tire pressure for each vehicle. Build a car, weigh it, do the math based on the tires it will be equipped with at sale, and then build a million more with a sticker that says the same thing. It costs more to print the sticker on the door, than they spent to do the math.

I agree that the car manufacturers probably don't spend much time determining optimum tire pressures vs. load, but you can bet that the tire manufacturers do. The car manufacturers' engineers probably just consult the reference data provided by the tire manufacturers and/or industry standards organizations (TRA [U.S], ETRTO [Europe], JATMA [Japan]) and then perform abbreviated analysis and testing to validate the recommended pressure(s) on their own, using ride and handling criteria appropriate to each vehicle model.. Remember, the effective spring rate of the tires is an essential component of the overall suspension design.

quote Originally posted by TONY_C: Is it just me or does it seem a bit ridiculous to have 61 posts about recommended tire pressures? Jeez

Management summary: If in doubt, use the pressure placarded on the car by the manufacturer. They know more about the car than you do.

[This message has been edited by Marvin McInnis (edited 04-30-2013).]

quote Originally posted by TONY_C: Is it just me or does it seem a bit ridiculous to have 61 posts about recommended tire pressures? Jeez

X2 plus is it just me or do they sound a lot like congress?
Sorry that came out sounding too much like an insult no one is that bad
edit to add my 2 cents on air pressure , more than flat and less than go boom is always good

[This message has been edited by kendallville (edited 04-30-2013).]

quote Originally posted by rogergarrison: Well first off, I was gone ferrying my plane down to the island. Im not going to bother crawling under my car looking for numbers. You turds would just find a reason to say theyre photoshopped or faked anyway. I run 40+ pnds in all my cars and it works fine for me. I really dont give a crap if you do or not. I laugh when my tires last double or tripple what you get running the awesome factory recommendations. Your the same birdbrains who change oil every 3000 miles....EVEN when the MANUFACTURER SAYS 7500 in most cases. So much for doing what the all knowing manufacturers say. Dont that make you hypocrites ? I DONT do anything a manufacturer recommends...I do what works for ME. Do whatever you want.

Quoted for posterity.

quote Originally posted by TONY_C: Is it just me or does it seem a bit ridiculous to have 61 posts about recommended tire pressures? Jeez

Whats better a V8 or a 3800SC?