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Old 05-30-2008, 08:51 AM   #29 (permalink)
CapriRacer
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Allow me to shorten:

Quote:
Originally Posted by adam728 View Post
You got it, he is saying that increased pressures reduce the fatigue life, but there is still a huge safety factor there. So the tread will be long gone from the tire before you get to that fatigue failure. ........

I don't think we know how large the "safety" factor is - too many variables. More to the point is that there is an element of statistics involved - tail end of the curve type stuff - that would influence the point at which a failure would occur due to fatigue. As you point out, there's a lot of variables. Things such as speed, road smoothness, etc. would all influence where that point is.

Just as a reminder, when the tire pressure is increased, the wear rate is also decreased, meaning the tire will wear slower - more cycles before removal. This is also going to complicate the situation.



Quote:
Originally Posted by adam728 View Post

.........

I stopped in front of a buddy's house and layed a little rubber with a quick stab of the gas. What was revealed was two burnout's probably around 2.5 inches wide each, from 285 series tires (probably around 9" tread width).
Too much pressure + too little weight = crowned tread and very small contact patch

........
If you watch videos of dragsters, you'll see that the black patch left by the tires is narrower than the full width of the footprint in contact with the ground. This phenomenon also exhibits itself in wear - tire wear on driven tires tends to be more in the center than on the shoulders. You can't see this in FWD cars because the driven tires are also the steering tires - and steering tires tend to wear on the shoulders. But on RWD sedans, for example, the rear tires will wear in the centers and the fronts will wear on the shoulders. Needless to say, this would be aggravated in an unloaded pickup truck where the rear tire pressure is specified for a load in the bed.
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Last edited by CapriRacer; 05-30-2008 at 08:53 AM.. Reason: Spelling, for heavens sake!
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