Blue sky...
On my BMI chassis I ran 1.75" diameter front and rear at the Holloween Classic at a high bite track... that gave me 3mm clearance front and 3 1/4mm clearance rear. I run purple fronts and grey rears, for me the magenta fronts gave a push to the car, but it was consistant, the purples heat up and get stickier as the race goes on and gives more bite. I don't know anything about the motors...

Wayne