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So with a 50-60lbs tool bag strapped to my tail I get some bad head shake at 38-45 mph. Like it almost gives me a tank slapper with my hands off the bars. With just me, or me with a passenger it's non existent. Bike is an 02 fz1 with race tech cartridges and what ever other gmd voodoo in the front and a penske out back, both sprung for 230# rider with gear. I'm a little over my ideal weight at 240 with no gear. The bike has been down twice. Once by the previous owner from a wheelie gone wrong. Once low sided by me at about 60 mph. The forks and triples have been straightened but never had the frame measured. I replaced the steering head bearings about 20k miles ago. The rims and tires are balanced with pirelli angels with about 3k miles on them and seem to be wearing evenly.
The only other time I experienced this with this bike is with an old crappy set of touring tires (dunlops I think) and I just wrote it off as old crappy tires, since it went away with new sneakers.
Anyone know what it could be? I was thinking Maybe the steering head bearings but that's just speculation.