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Originally Posted by Greenblazer
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Let me simplify and ask again, is it, or is it not safe to run tires at MAX sidewall PSI in your educated opinion? A simple less technical answer would be appreciated.
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I tend not to use terms such as "safe" and "unsafe" - too "black and white". I prefer to use terms such as "risk", which to me is a bit more accurate and descriptive.
So let me answer your question this way: Using up to 5 psi more than the vehicle placard pressure (assuming the same size as listed on the placard) is likely a small increase in risk. The footprint size and shape isn't much different and the tire's spring rate is only up at most 15%, so I don't think the handling will behave much differently (other than be a little more responsive). The impact risk is higher, but again this is less than a 15% increase in stiffness, and the risk of an impact event is fairly low to begin with, so while the liklihood of a failure from the event is somewhat larger, the overall risk is still fairly low.
Using up to the max pressure on the sidewall is a little more risk, but I've explored some of the handling issues when I raced. The only issue I feel uncomfortable about is the impact situation, but, as I explained in the paragraph above, the increase in risk of a failure is mitigated somewhat by the overall liklihood of the event in the first place. The problem here would be that sometimes tire impact failures lead to fatal accidents.