with 1.80 rear tires and 100 spur anywhere from 27-30 pinion - with the 27 tooth it's 1.527 - but it depends on the size and type of track you are running on - at Y- City in Zanesville, Ohio where I race,depending upon how the track is laid out I have used a 1.29 for a tight, technical track to a 1.81 for a more flowing faster track..........IMHO

also depends on the type of motor - I am taking about stock - and then again it depends on the type of stock ie smaller pinion for higher rpm motor.