Enrique, Enjoy your comments as always, however it is the "reputable sources" that has me concerned. How on earth could this conversation be considered "reputable" without any reference (or worse, discarded reference) to what was originally specified? Your octane rating and tire size examples reference original specification. Why not oil? Throughout this thread there is mention of temperature and operating conditions. What is the reader left with, though? Some vague idea that this might be important, perhaps, but nothing specific enough to warrant further thought? Perhaps the answer to this poor fellow's question is; "go ask a reputable source because you won't find it here"!