I bet that's the alloy drive cup. As far as the spur gear, I am going to power it mildly with low torque motors so I don't tear it up, that said I've only destroyed one spur... but that was from ingesting sand/rocks (on a Vaterra Kemora). That said, is there a certain KV or turn limit I should stay within?
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Yes, the alloy drive cup, -you need two ..one for front and back.
As for motors, I have always used silver cans for racing and 17t brushed for parking lot fun. The 17t brushed won't hurt it, ...I'd personally stay away from the fastwr brushless and lipo setups. I think extra torque could put too much stress on it. -that is just me though, as I know plenty of people ran brushless and lipos on the CR's without issue. The 25.5t brushless as described in the previous post should be fine as well.