I have played with both the 17 feels better to me because I can run a larger pinion and smaller spur which seems to not have as much drag on the car through the corners IE: Keeps the the "spool" up. With the 20 tooth it seemed as soon as I let off the car wanted to lock up. I normally run a 110 to 115 spur when running the 17 tooth. I had to run a 120 to 125 spur when using the 20 tooth. Yes the drive train has a little more resistance but I haven't noticed it on the track.