EcoModder Forum Fun video time! How many PSI to explode a 20 year-old, dry-rotted tire?

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 04-26-2017, 09:59 PM #11 (permalink) Master EcoModder     Join Date: Sep 2012 Location: Victoria, BC Posts: 1,308 Firefly EV - '98 Pontiac Firefly EV 90 day: 107.65 mpg (US) Little Boy Blue - '05 Toyota Echo 90 day: 33.35 mpg (US) BlueZ - '19 Nissan 370Z Sport 90 day: 17.19 mpg (US) Thanks: 43 Thanked 389 Times in 292 Posts Don't they time warp at 88psi or something like that?
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Quote:
 Originally Posted by darcane 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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Quote:
 Originally Posted by CapriRacer 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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Quote:
 Originally Posted by MetroMPG 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.

 04-27-2017, 01:46 PM #15 (permalink) Master EcoModder     Join Date: Aug 2012 Location: northwest of normal Posts: 16,689 Thanks: 4,422 Thanked 5,609 Times in 4,472 Posts 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.
 04-27-2017, 02:42 PM #16 (permalink) In the fasting lane     Join Date: Dec 2012 Location: Nieuwegein, the Netherlands Posts: 3,750 Red Devil - '11 Honda Insight Elegance Team Honda 90 day: 55.71 mpg (US) It - '09 Hyundai I10 Active Cool Team Hyundai 90 day: 29.19 mpg (US) Thanks: 1,521 Thanked 2,059 Times in 1,324 Posts I would think that higher tire pressure means the tire flexes less each rotation, so it should age slower? __________________ 2011 Honda Insight + HID, LEDs, tiny PV panel, extra brake pad return springs, neutral wheel alignment, 44/42 PSI (air), PHEV light (inop), tightened wheel nut. lifetime FE over 0.16 Gmeter or 0.1 Mmile. COVID-19: Some people just don't get it.
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Quote:
 Originally Posted by RedDevil 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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Quote:
 Originally Posted by RedDevil 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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Quote:
 Originally Posted by CapriRacer 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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Quote:
 Originally Posted by freebeard 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.