Quote from Dillyracer :

hehe, I got it down to 20 procent already today *proud*

Yeah, you've only done 26 races on CTRA-X so your ratio drops fast if you run a couple of races without causing yellows For me it takes a lot longer to make it drop as I've done a lot more laps.

Had it wittled down to 17%, and now it's going back up again

I managed to get mine down to 14% in 2663 laps.