Originally Posted by Smileyboy
Ok So I have converted the spur gear to normal 48p
gears. I have a 17.5 LRP motor. and a 13.5
What pinion should I use with these 2 motors?
Is there somewhere I can look which will help me to understand the final drive ratios? I have no idea what I'm doing in this area.
For starters, it depends on:
- what size spur you're using
- whether your track is tight and twisty, or open and fast.
- how good your batteries are
- how long your races are.
Talking about gear ratios in terms of pinion/spur can be deceptive - the final drive ratio and tyre diameter also have effect (and some tourers have very different final drive ratios). This is why most racers will talk of "roll-out", which is how far the car will move forward for every motor revolution. This way, if someone says "A Novak 17.5 will handle a roll-out of 35mm around here", you can use this to work out exactly what pinion you need to get this roll-out for your spur/final drive/tyre specs - its information that isn't specific to any particular type of car or tyre choice.
A Google search for "rc roll-out" should get you plenty of info. If if still isn't clear I can post a thorough explanation for you.
You'll find a good roll-out calculator here:
Now all you have to do is ask the locals what the appropriate roll-out is at your track for your size/type of motor, and then start from a slightly more conservative gearing than that. If the motor isn't too hot after a few laps then try adding a tooth or two at the pinion, but keep an eye on the motor temp - you don't want to cook it!
Most of the quicks at my twisty local track are putting back 1000-1300 mah into their packs after a 5 min race. Obviously, you need batteries that are of a high enough capacity to cope with the kind of drain you'll asking of them, or you'll be fading at the end of the race. 1900 NiCds just aren't going to cut it...