Mike just said the word I was going to use - I totaly agree, one of my freinds drag races a bike which he shares with 2 other riders. On the same day, the 3 riders each did 5 runs with only a rear tyre change about mid way. On 4 out of the 5 runs the results showed consistantly which rider was quickest and so on, even though only 0.5 seconds seperated them. They reckon it is 75% rider 25 % variables on the bike