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Assistance diagnosing front suspension

obrienl

obrienl

Bicycle
I've been trying to work through this but have not found the cause and am at a loss at this point.

I have been trying to work out a fast sweeper suspension undulation and my front end in a straight line was bouncing as if the front tire was badly out of balance.  I checked the tire, it was balanced.  Next was the thought that maybe the fork fluid had become too contaminated or aged to dampen properly (09 bike about 22 mo old with 26K on the odo).  I changed the fluid, no joy.  Then I thought (since I only have the capabilities of static balancing the tire) that maybe the tire had become delaminated or something.  I replaced the tire, no joy.  Next, was another fluid change to a different manufacturer, again to no avail.  I've checked and rechecked everything I can think of, including the steering stem adjustment and am now out of brain power.

Any suggestions?
 
OK, i am not going to say that i am a suspension expert at all...but i do have 18 years of riding, 12yrs of trackdays, and 5yrs of road racing...i have tuned my share of bikes in my riding lifetime...so let me start with this...
:motonoises:
" a fast sweeper suspension undulation and my front end in a straight line"

describe what this exactly feels like to you when you ride please.  does it get worse as you go faster?  is it a rythmic repeating bump, wave, oscillation coming thru the chassis and/or the handlebars?  Does it come thru during corning, or get worse or better?

have you turned the screws of your C14s suspension at all since you started riding it?  do you know what your preload & rebound are set to currently?  have you tried to make changes to try and tune this problem out?

Let me know...I surely would like to help, as would others...

I have fiddled with my own C14 since i took possesion of it in June, and it does take some trial and error to get it to feel the way you might want.  i have it just a bit softer than a normal supersport.  it turns quickly, and is very stable thru mid corner...but riding straight up and down, its not as twitchy as my previous RRs.  I know some like a more plush ride for longer touring duty, and some want a tighter ride for more canyon carving (with comfort of course).
 
In a straight line the front wheel bounces and is much more noticeable under acceleration.  Since one of my steps was to replace the front tire I don't think it is the tire.  On the best of pavement it still bounces under accel.  The onset of the front sweeper undulation, which occurs through out the entire corner, was in the spring.  I have deviated in my suspension settings trying to tune this out to no avail.  I always return to my origninal settings then begin again.  I am set with 3 lines showing(not sue what that is in mm).  Rebound is at 4 click from seated.  The rear is set at 20 from full out and 3/4 out on dampening.  I am about 220 pounds of short fury in case that helps  ;D

I don't necessarily believe that both issues are related.  I am sure that the sweeper wobble is definately a suspension setting issue that i am not smart enough to figure out.  The front end bounce could be in the forks or the wheel/tire.

I have to change out my friends fork fluid on Monday and am planning on using his wheel on my bike to either eliminate the wheel or forks as the source of the bouncing.
 
Sir;

Its not your folks or suspension.  I believe that you have a warped rotor.  What its doing is the small warp is rubbing the brake caliper and causing this vibration.  It can make the bike feel like it has an imbalanced tire or bent rim.

To prove, or disprove, this...put the bike on its center stand, and spin the front wheel.  it will either give you this same rhythmic feeling or the wheel will slow or maybe even stop as the warped section of the rotor comes in contact with the brake pads.

Try this and see what you can find.  Rotors are very easy to replace, they just cost waaay too much buying OEM from the dealer.  If it were a sportbike, i would say just go online and find yourself some used rotors from a trackday guy or buy some after market ones.  or maybe even ebay a set.

Let me know if this helps.
 
OK I am an IDIOT.  Maybe not quite an idiot but.....

I put my friends front wheel on and there wasn't any difference in the ride.  So I was thinking forks are the key.  After changing out my friends fork fluid this morning I decided to take off my forks, remove the top plug, drain the fluid to check it.  The fluid was pristine as you would expect being two weeksish old.  When I assembled them both previous times I set the top plug to the closet "click" to the specified 13mm without being under.  On one side that was about .26mm over and the other .03mm over if memory serves me correctly.  Today, when I set the gap as it were, I went between click to get within .01 of the 13mm.  I re-assembled and test rode.  My front end bounce has been solved.  I didn't think that such a small of adjustment would matter.  Apparently, on my bike it does.

Thinking this might be my issue I set his forks up the same way.

For the fast sweeper wobble, I will have to eventually travel somewhere to have someone with more experience help me get the suspension setup properly.
 
8)

hey, maybe i am the idiot.  i had that issue with my trackbike a few years back, and it turned out to be one of the rotors. 

Well, glad you found the problem...good luck
 
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