I noticed on my new tr arena today sparks from underneath on acceleration. On inspection the spur gear is hitting the chassis at the rear of the opening only slightly. All bolts are tight & nothing is bent as it is new & has not been jumped or crashed. Does the chassis flex that much? I was thinking about buying the alum. center brace , but is it stronger than the one on my RTR or is it just "bling" ? I guess i will prob. dremel just a little more clearence. Any ideas ?

After being doubly sure everything is adjusted right and you still have that issue, I'd just hit it a bit with the dremel. I'm not real positive, but I don't believe the alum center brace fits as a direct bolt on, on the TR

The upgraded brace fits fine, it's exactly the same size. I wouldn't worry about the sparks, eventually the spur will make a tiny bit of clearance for itself and it should be fine. If you experience very worn clutches, or lagging acceleration/speed, then either sand some material off, or grind a bit with a dremel.