front end wobble at 40-45 mph

My 05 Suzuki Boulevard C90 has approximately 18,000 miles, well-balanced tires, and the correct air pressure.  However, after installing aftermarket "T-Bars," it has developed a front-end wobble around 40-45 mph.  I have been told the problem may be in the head/neck bearings, and they may need to be replaced because the stock bearings are only good for around 18-20,000 miles.  I have also been told the problem may be the kind of tire, and/or tire pressure, etc., etc., etc. Does ANY of this sound logical? (My experience consists of building two Triumph choppers, and a 1952 Harley panhead chopper).  My email address is perdidodesperado@yahoo.com. Thank you.  WP  

Wobble is caused by off center friction as the front tire goes down the road. This is usually the result of an unevenly worn front tire. Common contributing factors are incorrect spacers on the front axle, so the wheel isn't centered, fork tubes mounted so the length below the steering head is not exactly equal and low front tire pressure.

Tightening the nut on the steering head pivot bolt can hide wobble by increasing the pressure and tightness of the steering. Unless you can feel the steering 'clicking' into position because the bearings are deformed, the bearings are fine. Loose steering head bearings that are not deformed, will not 'cause' wobble, although they will allow wobble if something else causes it. Overly tight steering head bearings will deform after just a few thousand miles.

Many bikes have a single brake disc on the front wheel and the wheel located slightly off center. These bikes will always develop a wobble as the front tire wears. Most of the time the wobble is just a slight tendency to wobble as the bike passes through 30 to 35 mph and merely keeping both hands on the handlebars is adequate to damp it out. The slight wobble is usually more noticable when the tire is cold.

'Correct' tire pressure is difficult to determine. The bike manual tells you the minimum 'safe' pressure for handling, not the correct pressure. The tire manufacturer tells you the maximum 'safe' pressure for the tire under load, not the 'correct' pressure. Your 'correct' pressure will be a compromise between those two limits. The higher the pressure, the more resistant the tire will be to uneven wear, so it lasts longer before causing wobbling. The lower the pressure, the smoother the ride will be on poor road surfaces, but the tire will be more prone to uneven wear and early wobble.

Wobble that is more noticable in the turns or on rough roads is usually due to uneven friction in the front shocks. This can usually be fixed by replacing the fork fluid.

regards,
Joe