Handlebar wobble (it's not what you think)

[VTFJR13]

There is also a possibility that your new tire is not right. Just because it is new doesn't mean it is good. Either not round radially or straight running axially. You can measure the tire runout on the bike, same as you did for the wheel rims.

Ye

I would have to agree with Fred on all counts here. Especially this last one. My experiences over the years on any of my motorcycles that developed a front end wobble at certain speeds was the tire. Yes is it possible to get two different brand new tires with a problem. I have had a new tire act worse than the old one I just took off.

 

[charismaticmegafauna]

Au contraire, mon amie.

OK, I'm with you -- we're tilting the whole bike with these changes.

I still maintain that it's caster (rake & trail) that causes steering oscillations -- just like a shopping cart pushed too fast.

Since the normal changes to a motorcycle's geometry (tilting) easily happen in a rear-ward direction -- adding equipment/weight to the rear, sagging rear shock spring, rear-ward seating/loading -- I surmise those changes are contributors to handlebar wobble.

There certainly doesn't seem to be much opposite evidence -- "I leaned forward and my handlebars started to wobble."?

Of all the participants involved in the handlebar wobble/steering geometry conundrum, caster/rake/trail changes (just) appear to be the cause...?

 

[Fred W]

Purely from a semantics / pedantics standpoint, the steering geometry and its inherent degree of (in)stability or the lack of steering stem (bearing) preload / dampening are still not the "causes" of steering oscillation. What they do is make the system more or less susceptible to oscillation once it has been initiated by some outside stimulus. That has to either be something in the rotating mass of the bike (front or back wheel) that is either not balanced well enough or or not running true enough, or else some turbulent aerodynamic fluctuation that initiates the wobble. Having lax steering angles or highly preloaded (tapered) bearings makes the system less likely to break into oscillation when a given amplitude of that moving stimulus is applied.

Unweighting the front end of a bike has two effects outside of any steering geometry changes. The steering bearings will have less friction and the friction of the tire contact with the road surface is lessened, both of which result in less dampening of potential oscillations.

 

[phroenips]

Problem update:

I finally got around to installing tapered bearings, and aside from an ***** mistake (hint: the dust seal on the All Balls kit needs to be slid on the steering tube before the lower bearing gets pressed on...dammit!), it went smoothly, and I am pleased to report that my handlebars are once again rock solid. I'm not sure it if was just due to re-tightening everything, or if it is the tapered bearings themselves, but at this point, I'm not sure I really care

 

[03HiYoSilver]

Glad it is working well for you now. Thanks for sharing your findings.