Gearing is quite simple.
The higher the ratio = faster acceleration
The lower the ratio = Higher top end, slower acceleration.
Your car will have something called an internal ratio.
this is the diff pulley divided by the centre pulley (the centre pulley is the one that is on the same shaft as your spur gear, and rotates when you rotate your spur gear.
To find your ratio, you just divide your Spur gear by your pinion and then times it by your I.R.
(DR)*(IR)=FDR
So for example, on a tight indoor circuit with my non timed 13.5t TRF417 this is how I would calculate it
TRF417 details -
Spur =111t
Pinion 38t
Diff pulley = 37t
Centre Pulley 19t
So I do the sum
(111/38) * (37/19) to get my FDR which is 5.687
the working would be
DR = (111/38) = 2.921
IR = (37/19) = 1.947
2.921*1.947 = 5.687
So if you ask about at your local club you will find a general ratio people use so you can range your pinion or spur to get in the same sort of ball park. As has already been mentioned, you want to get to top speed 3/4 the way down the longest straight or if its a small tight track you want that to be more like 1/2 - 3/4 down the straight as these tracks are more about the infield.
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