Board Thread:Game Discussion/@comment-27095714-20170729084006/@comment-29898480-20170729133049

I don't think it means PR is random, it just means PR is calculated differently. Your system assumes all linear relationships, too, whereas cars can have quite different performance even with an identical stat.

Imagine a very light, low power car, and a very heavy high power car. Both could have the same 0-60 time, but they don't have the same acceleration characteristics. The light car jumps off the line quickly, but acceleration tails off as speed builds because the power gets overwhelmed by the air resistance. The heavy car is slow off the line - it's heavy! - but with the big power it keeps accelerating to very high speed. The two cars happen to reach 60mph in the same amount of time, but otherwise the acceleration performance is quite different.

PR is (I hope!) FMs attempt to quantify these types of differences into an overall performance score. It's needed/useful precisely because the 4 numbers we're given don't fully capture the performance dynamic. It's also inherently arbitrary, as you need to make value judgements about how to weight factors in developing the PR formula.