Originally Posted by
sheetmetal2
What am I missing? The internal drive ratio is 1.7 like you thought. 3.5 inches converted to mm is 88.9. Using Gearchart.com and the numbers that you gave me (96 spur and 40 pinion) it comes out to 46.2 mm. That converted to inches is 1.82. What am I doing wrong?
Novak recommends FDR = 3.5
PDR x DTR = FDR
See the attached zip file, which contains an Excel spreadsheet for Xray Rollouts. If you need to change the spur, change the value in Cell O1 and press enter. The top chart is rollouts in mm, the bottom chart is rollouts in inches. The top row for each chart is wheel diameter, and the left column is the pinion tooth count. To find a desired rollout, start with the tire diameter, go down the column until you find the rollout you want, then find the pinion you need for that rollout.
So for the desired rollout of 1.82 inches, a 60mm tire gives you a 40 tooth pinion. Note that the columns are the same tire diameter across both charts (60mm = 2.36 inches)