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Old 04-26-2017, 10:59 PM   #11 (permalink)
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Don't they time warp at 88psi or something like that?

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Old 04-27-2017, 09:00 AM   #12 (permalink)
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Quote:
Originally Posted by darcane View Post
Cool video, thanks Metro.

I wonder what it's rated pressure is, probably 35psig for an older tire? If so, that's still about four and a half times it's rated pressure.

Typically in engineering, things are designed to a safety factor. Safety factor of 2.0:1 means that it was designed to twice the rated load. For the products we design where I work, because the failures could cause death, safety factors are 4:1, 6:1, or 10:1. I can see tires being in the same category, so I would expect a 4:1 or 6:1 safety factor. I'm impressed that the tire still has such a high burst pressure considering it's age.
Don't forget about fatigue. In tires, that's the most important thing.

If you look at a typical S-N curve for rubber - and consider that 100,000 miles is about 6 million cycles - then the S-N curve says the failure stress is about 1/4 to 1/5 the static value. If you divide 220psi by 4 or 5, you get 55 and 44 psi. Isn't that interesting!
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Old 04-27-2017, 10:23 AM   #13 (permalink)
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Quote:
Originally Posted by CapriRacer View Post
Don't forget about fatigue. In tires, that's the most important thing.

If you look at a typical S-N curve for rubber - and consider that 100,000 miles is about 6 million cycles - then the S-N curve says the failure stress is about 1/4 to 1/5 the static value. If you divide 220psi by 4 or 5, you get 55 and 44 psi. Isn't that interesting!
Of course, they did say the tires were dry-rotted and old.

Don't ever plan on running tires that old.
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Old 04-27-2017, 02:01 PM   #14 (permalink)
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I'm not going a pound over 125. I like the smoother ride of the low 100's.
Though when I stop to think about it, skinny little road bike tires normally inflate to 120 PSI or so.
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Old 04-27-2017, 02:46 PM   #15 (permalink)
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I had a set of the really nice European Klebers (they changed when they set up manufacturing in the USofA) on my 1956 sunroof Beetle. I parked it on dirt at my brother's place for 18 months and some micro-organisms in the soil ate the tread off one of them! The flat spot made the tire unusable.

jamesqf — pneumatic tubes of a given wall thicken can withstand more pressure in a small diameter, less as the diameter grows.
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Old 04-27-2017, 03:42 PM   #16 (permalink)
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I would think that higher tire pressure means the tire flexes less each rotation, so it should age slower?
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Old 04-27-2017, 07:26 PM   #17 (permalink)
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I would think that higher tire pressure means the tire flexes less each rotation, so it should age slower?
Yes, but impact stresses could make it easier to puncture or blow, that said at the pressures we run it's mostly a non issue
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Old 04-28-2017, 08:49 AM   #18 (permalink)
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I would think that higher tire pressure means the tire flexes less each rotation, so it should age slower?
If by that you mean less likely to crack, that would be so. But aging is more about the chemical and physical state of the rubber - how well it's strength is holding up and how well it is adheres to adjacent components. It's those things that cause the tire to fail. And those things seem to be more correlated to heat.
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Old 04-28-2017, 11:08 AM   #19 (permalink)
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If by that you mean less likely to crack, that would be so. But aging is more about the chemical and physical state of the rubber - how well it's strength is holding up and how well it is adheres to adjacent components. It's those things that cause the tire to fail. And those things seem to be more correlated to heat.
Heat is also correlated to pressure. Underinflated tires get very hot on the highway. I had a slow leak in my right rear and it was almost too hot to touch even though it wasn't riding the rim yet.
The other tires were about at ambient running 42 PSI.
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Old 04-28-2017, 01:44 PM   #20 (permalink)
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Quote:
Originally Posted by freebeard View Post
jamesqf — pneumatic tubes of a given wall thicken can withstand more pressure in a small diameter, less as the diameter grows.
Yet on the other end, semi truck tires get inflated to around 100 PSI.

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