Originally Posted by
SpikedLemon
It's a baseline for comparison that gives a very good indication for ranking.
Relative rankings don't determine how fast you are. Watts do.
Don't forget to onsider that you don't put your full weight onto a single tire: perhaps 55-60% of it at the worst case. 42.5kg would equate to, roughly, a 90kg rider+bike (200lbs)
The other carries the rest of the weight, at the same Crr, so you can scale to match the total.
Riding Gatorskins instead of GP4000s costs you 15-20W at 20 MPH, which can be the difference between suffering and a pleasant ride or running out of power after 10 minutes not an hour