Originally Posted by enigma
Until we can control for tires charts like this are of limited value.
Not true because this is a statistical approach (the power of n).
Even if we control for tires, we run into other uncontrolled variables such as weather, driver skill, driver mood, etc. That issue has been debated to death on various threads here. I am not saying we shouldn't control for what we can control for, but the point of pooling together a large database is using statistics to even things out. One can calculate a 95% confidence interval as a performance envelope for instance. That obviously doesn't mean much for making sense of an individual data point, and 29 cars do not make up a large database either. However, if we were to add 200 data points to the chart, then the outcome would make me have more faith in the regression line as the confidence interval would most likely get tighter.
That said, even with 29 cars, you can arrive at some observations. We know for a fact that the CSL was on slicks. Draw a straight line between the CSL point and the 997 GT2 point, which ends up being pretty much parallel to the regression line, and some std deviations away from it. Any car below and to the right of that line, regardless of what type of tires its on, is either breaking some exciting new ground in engineering or is bogus. 480hp GTR falls into that category. However, we don't have enough information to say that is indeed new territory or just bogus. Time will tell.