Showa shock spring "resonates" @ certain RPM

[cr250john]

My '00 CR250 showa shock spring (5.2 kg/mm) hits a resonate frequency at a certain engine RPM and it vibrates like crazy. It happens while I'm sitting on the bike or on the stand at this "critical" RPM. The sag settings are correct for my weight.

I'm beginning to wonder if this vibration is translated into the bars causing fatigue of the arms. :think It seems to happen at an RPM I typically use.

Have you experienced this and is it typical for shock springs to do this? Is there a "cure" other than don't run the engine at the "critical resonant spring frequency"?

Your thoughts....

 

[marcusgunby]

All springs will resonate at a certain frequency.To stop bad vibes i fill my Cr bars with RTV.

 

[Jeremy Wilkey]

The bigger the bike the worse it seems.. The AF at about 1/3 throttle really hums with a 5.4 :)

 

[cr250john]

Thanks Marcus & Jeremy,

I'll put up with the vibration for now. I just happened to have the bike on the stand with the engine running and while revving up the engine, I saw the spring really vibrate at a certain RPM. Seemed to shake the whole bike.

Thanks for you thoughts!

 

[Jaybird]

Marcus,
I've been thinking about filling my bars with silicone as well. Any cons, that you know of?
BTW....I was wondering about what was shaking the bejeeezuz out of me at times. I think I found the answer thread!

 

[Murf]

resonant frequency

CR250John,
Keep in mind that when you are on the bike and riding with the spring compressing and decompressing that the resonant frequency will be changing, and therefore the likelihood of the vibration being transmitted up to the bars will be lower.

 

[marcusgunby]

I originally had twinwalls on and they vibrated like an angry bee:scream: i now have TAG RM high bend filled with silicon and i hardly notice the vibes(and im real fussy)the only downside is its messy to do and they weigh about 1lb heavier-no real problems at all.:D

 

[cr250john]

Re: resonant frequency

Originally posted by Murf
...when you are on the bike and riding with the spring compressing and decompressing that the resonant frequency will be changing, and therefore the likelihood of the vibration being transmitted up to the bars will be lower.

Right you are!
Just thought it was an interesting topic to add to the dirtbike vibration syndrome.

Thanks to all for your reply!