I used an 81 spur with a 49 pinion to achieve 4.0 final drive. I was able to go down to a 46t pinion with that spur but the motor was pretty close to the shaft. So I'm guessing you can go down 1-2 tooth lower until you run out of room.
3.5 fdr isn't bad, just watch your temps. I've gone as low as 3.19 last winter.
Originally Posted by
redbones
Thanks for the quick reply.
I'm going to run my LRP TCspec with a 17.5Duo(middle hole). The track has a 120ft straight and top speed do matter. Some people have suggested a 3.5fdr, but I think that is too much. I am looking at around 4.0. With the current pinion set that I have, I can go from 38 to 46. Which means I need a spur of about 75. But What worries me is the amount the motor can move. I don't want to buy a gear set that I won't be able to mesh at all. What would be a safe spur/pinion combo to achieve the FDR for the 17.5 class? Thanks