I ordered the Worlds Edition because I like to start the season with a fresh car
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Hopups :
Alu hubs : always ran the plastic ones and never broke one. Performance wise : lower unsprung weight is ALWAYS better, so I'll be replacing them with some new plastic ones.
The larger pulleys will definately improve things since everyone here running a TRF501 (including myself) has had problems with belt wear and belts snapping (we run on astro a lot)
upgraded ball studs : They will directly be replaced by Hotbodies ballstuds and Losi ballcups. The plastic on the original TRF501 ball cups is way to soft, causing them to pop off frequently.
reinforced upper arm mount : sounds nice but never had a problem with the kit ones.
I actually like the delrin damper pistons. They seem to make the shocks leak-proof and the feel is a lot more consistent compared to the kit ones.
If you run a BL, the revised body will be a welcome feature. On my current body, the sensor wire rubs the body.