Hi Andrew S
However, I note from Team Novak's recommendation that if we compare these 2 methods, then there would be difference in Spur and Pinion sizes
For instance 21.5T Motor, the recommended gearing by applying FDR is 3.40.
Whilst for Rollout formula, the recommendation is 2.8".
If we use 45mm rear tires and 90t Spur, then the pinion would be 45t.
The gearing shall be 2.00, which is a lot taller than the above FDR's recomemndation.