front end vibration

[RideFz6Style]

Hopefully this doesn't scare you all but I'm looking for some advice on things to check before I take my baby to the shop. This is something that I encountered recently, but it's bothering me thinking about it. So the problem is, when I get to around 100 mph, the front end of my bike starts shaking a lot more than it should be, a scary amount honestly. The motion goes through the handle bars and is in an up and down sense, no left and right. I don't feel this vibration at all through any rev range up to this point. This is making me think that my tire may be just slightly unbalanced and I am only feeling it there due to the speed. Until I get this fixed im gonna stay away from that speed. Any other suggestions before I take the tire to get checked? Thanks in advance for your advice.

 

[Carlos840]

I would start by checking tyre pressure, then realigning the forks, make sure the top clamp is tight, then loosen everything south of it. Press the bars down a few time to let things align themselves, tighten everything.

Here is a good video showing the full procedure:

https://www.youtube.com/watch?v=vSunBRB6-r8

If that doesn't help check the tyre balance.

 

[deeptekkie]

Like you, my first guess is tire balance. Carlos840 has some great advice as well. Do your brake rotors seem at all warped? Since you describe it as up and down motion I would think tire balance, (with perhaps some slop in the steering head bearings)? Just a thought.

 

[FinalImpact]

Simply put; while at normal speeds its a non-issue, but imbalance becomes evident as death approaches (I mean speed increases to 1XX). So, have the balance checked again. Perhaps at a different shop with a different method (static vs dynamic). Most shops do a static balance while others may do dynamic or spin balance.

When is the last time the fork oil was changed? I usually don't like trying to hide issues as its most likely a balance issue and doing things to fix the suspension usually just masks the real problem. Remember the old metal gyroscope tops you wrap a string around it, pull it, and you can spin it on your finger?? They have no damping and spin until they loose inertia. But if out of balance, no damping will allow the "imbalanced one" to spin as long as one which is balanced properly. The same thing applies here.

That said, if the labor balancing does not solve this, you might see what changing the fork oil and maybe the springs do for it. Whenever a spring is involved there is almost always a resonant frequency or oscillation that the suspension just can't control. That is, the damping efforts of the forks are nil at certain frequencies as it matches the springs oscillation rate. So, change your fork oil and it may change what speed this occurs at.

 

[Erci]

My guess is that the tire is either out of balance or it actually has a small imperfection.

If there's a CycleGear near you, they will likely check the balance for free. You can also ask them to look at the tire when it's spinning to see if there's a slight elevated area at some point.. or a dip. You can check this yourself by pulling the brake pads out, so you can spin the wheel freely.

 

[RideFz6Style]

Thanks for the input guys. The tires are getting pretty worn and need to be replaced soon anyways, so I may just buy new tires and have them balanced to be sure there is no tire imperfection.If that doesn't fix it, I will do the fork oil change. Seeing as I'm in a System dynamics and vibes class right now, I definitely understand what you're saying FinalImpact.

 

[motojoe122]

My guess is that the tire is either out of balance or it actually has a small imperfection.

If there's a CycleGear near you, they will likely check the balance for free. You can also ask them to look at the tire when it's spinning to see if there's a slight elevated area at some point.. or a dip. You can check this yourself by pulling the brake pads out, so you can spin the wheel freely.

I had the same issue, well sort of. Long story short, front tire turned out to be defective. It had a slight bulge in it. New tires solved the problem.

 

[ozgurakman]

Same issue on mine but not scary just annoying.

I have new set of tires but rear wheel has a little bent on left lip. Also head bearings needs to changed. Most vibration gone when I changed the tires but bike has still a little vibration on front end, not scary...
Also you should check front tire bearings.

 

[TownsendsFJR1300]

Thanks for the input guys. The tires are getting pretty worn and need to be replaced soon anyways, so I may just buy new tires and have them balanced to be sure there is no tire imperfection.

Worn tires alone will cause issues as they'll cup over time, if the were out of balance, they'll wear unevenly too....

New tires makes a world of difference!!