I tried sand. I dont think it worked well though. May have to try lead, guessing the heavier the better?
One more suggestion that worked very well for me. I removed the plastic caps from the inside of the handle bars and pressed in a chunk of grounding rod. The rod is slightly oversized so measure carefully. Once it is pressed in it could prove interesting to remove. I wish I had kept my measurements; overall the ground rod adds close to 1/2lb to each bar.
I would like to drive the rods out this winter and fill them with molten lead. Cold rolled steel (ground rod) has a specific gravity of 7.83 while lead is 11.35
A person would end up with some serious bar weight with them filled with lead.
I think I posted pics here a couple months ago, but I have a fully rubber isolated handlebar mount on Shoodaben. Wow, that's sweet! I am trying to do production on it, but so far the fellow who is supposed to do the manufacturing has had excuses, not parts. I'm working on it... Steve
Here's another pic
just a thought but would filling the bars either with silicone only or the expanding foam make much impact do you think?