Now that I've got a rider of my hand I wanted to encourage them.

My kid has a Diamondback Clarity Junior which has 24in x 1.375inch tires with a max PSI of 55.

I've torn the bike down and put it back together regreasing the bottom bracket (it was a loose ball) and the hubs.

What else can I do to the *bike* (I know they'll get faster with time of course) to get him to rider a bit faster:

a) Would getting narrower tires or tires with a higher PSI help?
b) Putting drops on the bike so they are in a more aero position.

Kid weights all of 75 pounds!