Honestly, if you are racing on rubber tire metal hubs and steering knuckles are not needed. If your hitting things hard enough to break bearings then the smaller bearings found in the metal parts will become a bigger issue for you - not to mention the metal parts will bend. My recommended is to:
#1 buy a bunch of cheap bearings - $1/each from an online retailer like avidrc. - replace bearings often.
#2 buy a bunch of replacement 14mm and 16mm screws as I bet you are bending your arm mounts with hard hits
#3 get the xray hard bumper
#4 lift off the throttle some times
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