filippimini

Racing 21.5 Blinky Touring Cars.

I'm looking for more speed on the straights.

Am I correct that a lower final drive will give me more speed but less torque?

Is there any advantage to changing the spur vs the pinion in order to achieve the lower FDR.

For example, with a 1.9IR
42pinion and 65spur = 2.94FDR
46pinion and 71spur = 2.93FDR

Both are almost the same, but is one better than the other and why?

wrenchdoctor

iTrader: (68)

Lower FD will indeed give the car a higher top end while taking acceleration away.

There is no real advantage to changing one or the other. If you want to make big adjustments to the FDR, change the spur. One spur gear tooth is about like changing 2 pinion teeth (its not exact but you get the idea). Pinion is more for fine tuning once you get it where you want it.

I dont think you are going to see a huge difference between those two FDR's, you might not even notice a change. You would feel a difference between 2.94 and 2.90 though.

MarkA

iTrader: (21)

You are correct except for being backwards on the pinion/spur ratio change effect. A tooth on a pinion is generally like 3 on the spur. For example, when trying to lower the ratio, using only the p/s ratio, if you went from 100/25 = 4.0; drop a tooth on the spur and at 99/25 you get 3.96. Go up a tooth on the pinion to 100/26 and it is 3.85. Pinion is the bigger adjustment in a single change, spur is fine tuning.

MarkA

iTrader: (21)

If gearing doesn't do it, and I doubt it will by itself, that will be because in a "slow" blinky class, it is all the little things that add up to straightline speed. Do you have good bearings that have been degreased? "Big" battery? Car at min. weight, etc. etc.?