The newer HD's are pretty much straight ahead freeway cruisers. The ones I've owned could be made to go and handle decently by stripping off all the unneeded weight and doing a lot of mechanical work. But now, a lot of the weight is in the rubber engine mounting system and the whole engine is under the spell of electromagical wizardry, which severely limits what can be done to bring it out of it's EPA induced coma.
As for the sparkplug, the base was still crimped, so it was most likely that the flange on the ceramic part failed. The ceramic is probably still where it landed in the desert maybe 1/2 mile or so west of the "YUMA 28 MILES" sign, I don't intend to go look for it. Fortunately, this was the right side plug (the bike has dual ignition) so the S&S air filter and the cooling fins took a good part of the impact. The edges of 2 of the fins were chipped and the chrome is seriously burnt on the air filter cover. When we got it, it had some junky japanese carburettor with a round filter. Had I not replaced it, this could have been a lot worse.
