I have read the posts on this thread, and I think that the only way to help with the hands going numb, will be to adjust your riding style, and change to a softer more cushioning set of grips. I've never tried changing the weight of bar ends, but that is interesting, and might be worth a try. I also ride a 2005 ZX636, and when I first started riding her, my hands would occasionally go numb. I have since learned to hold on more with my legs, than with my arms, and this helped me a lot. I do occasionally get some numbness from the vibrations, and have simply learned to live with it. Good luck.