Again thaks, for the replies, I will keep plugging away till I find an answer.

As I've pointed out earlier in this thread, I probably would have accepted the wobble as being a "normal thing", except for the fact that the wobble on my son's bike is much more pronounced than on my 2009.
I think what I'm going to try and do when I get some time is get a video while following bike to compare how the 2009 wobbles slightly then corrects itself right away (almost un-noticeable and feels stable), while the 2007 the wobble almost needs conscious effort to stop the wobble. (very noticeable, and has an unstable feeling.)
Might try and get the video next weekend, if I can.

 

I understand. I hope you get it fixed. Good luck!

 

Have you checked to see if the front wheel is balanced? An unbalanced wheel will give you vibration, especially at higher speeds.

 

I think this was also mentioned by someone earlier,,,,
I got another chance to ride my son's bike to work and back today, and I think I may have felt a shimmy in the front end, indicative of an out of balance tire. I guess that's the most logical place to start.

 

Cupping, also called checking and maybe some other names, is when the tire tread block rolls under causing more wear on the trailing edge. You can feel it when you rub your hand circumferencially around the tire. Going one way it will have a kind of smooth feel as your hand passes from the higher edge on the leading block to the lower edge on the next block. Rubbing your hand the other way you will feel the raised edge of the trailing block being higher than the edge of the leading block. On an extremely worn tire you can actually see the cupping.

As the tire rolls, the forces will roll the leading edge under, causing more wear on the back side, kind of like a windshield wiper the edge that would touch first will roll under and the trailing edge will be in maximum contact. Since the only forces on a front tire are mostly in the same direction it happens.

If there is any sort of alternating pattern of blocks side to side it will definitely cause a wobble when hands are off the bars. If bad enough, a severely worn tire that has noticable cupping, it can actually be felt through the bars, but holding the bars will dampen the action.

The coarser the tread the faster the wear. I've seen square block trials pattern front tires where the blocks looked like mini ski jumps.

Even the back tire will cup too, but in a different way. Circumfrencially the braking/deceleration wear offsets the acceleration/driving wear, so it is pretty much smooth either way. The back tire cups side to side. On a road or dual sport tire you will feel the difference when rubbing your hand side to side. The cornering forces are one way causing side to side cupping.

At the bike shop we had street riders complain about the wobble, sometimes with less than 1000 miles on a street tire, but usually only when hands off coasting down from 50 mph, wobbling between about 40-35 mph. Big tourers were hardest on the tires due to the weight on the front wheel. Even a small amount of cupping can start a light wobble that will amplify if not stopped.

Take a look at some tires, rub your hand around the front tire around the tread one way then the other. Do the same on a worn rear tire, but go side to side. You'll understand what I'm talking about.

Amazing part was how some customers complained about handling after a new tire was put on the front end. They were so used to the bad handling of a worn tire they weren't ready for the correction in steering.

 

I would think an out of balance wheel would cause an oscillation up and down. But then again, I've never had that problem... at least to my knowledge. I do balance my wheels when changing tires, but I've lost weights and never actually noticed it to speak of.