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Suspension tune 3

Posted August 27th, 2013 at 11:54 PM by Lychee

Another ride on Uvas and I noticed that the front end has a jackhammer effect on power that was not there before I upgraded the front. The front wheel seemed to get air time between a series of small bumps. I read a post by Dave Moss on another forum somewhere where he mentioned one of the things he suspected caused front end chatter on braking was not enough compression damping. Well, I was mostly engine braking, but let's save that tidbit just in case. I also asked a racer friend and, after discussing the changes I made, he decided that the effect was caused by excessive rebound damping. That's interesting, because reading on the internet tells me that there is too little rebound damping. Well, given that a front end chatter caused racer friend to crash a year ago on old santa cruz, I felt that he probably made it a big deal to figure out how to fix the problem. He said that the problem has reoccurred on the track when his fork oil was old and needed to be replaced because it was like a sludge being forced through the damping holes in the fork. Sounds a lot like hydraulic top out. OK sold. I went to road rider today and bought 10 w fork oil to replace the 15 w currently in the forks.

I put the bike back on the rack and noticed that my ziptie / sharpie indicators showed that the forks had nearly bottomed out on the last uvas run! Ok well I will do both things that I learned about. I dropped the forks and changed the following:
fork oil from 15 w to 10 w
air gap from 110mm to 130 mm spring out, emulator in.
compression spring preload from 3 turns to 5 turns. Port side was at 4 turns originally (whoops), but both are at 5 now.

Having done this 3 times already this one went by pretty quick. Disassembly and reconfigureing the settings went down without any problems. I did notice that the preload spring uses a 9/64 hex bolt. That is pretty rare size, about 3.5 mm. I found one with my drill bits. Lucky! Well not really, I could have used slip joints again like I did last time. After installing the forks really loosely, I placed the wheel in position and rested it on a block of wood on top of two old bars. I undid all the fork bolts and allowed the wheel to settle on the block. Then I lined up the axle and drove it in. Next, I measured the fork protrusion above the triple tree as 10mm each side. Then I tightened the fork bolts, took out the wheel, popped in the fender, and reinstalled the wheel and torqued to 65 foot pounds. Free spin!

After getting in the last fork and beginning to button it up the fairing, I noticed that I had installed the starboard fork on the wrong side of the handlebar control cables. Aww man. I decided that it was easier to remove the triple tree than to take out the fork again. After remove and reorganization I torqued the triple tree lock nut to 35 foot pounds. Fixed. Cleaned up everything else and tried a test okie doke around the complex.

Bike seems to be pretty plush on the okie doke, even when hitting speed bumps. Took her to the street. Seems to be very responsive! Can't wait to hit uvas again.
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Comments

  1. Old Comment
    Lychee's Avatar
    Bike was very vague in the front at speed when I tried Uvas. Kind of scary to ride leaned over. It felt like the handlebars wanted to oscillate more than I was comfortable with.
    Posted September 4th, 2013 at 09:27 AM by Lychee Lychee is offline

  2. Old Comment
    Lychee's Avatar
    So.. After reading all these articles on fork tuning, I went and checked the tire pressures. The rear wheel was dangerously low and front was getting there. No wonder it was so hard to push the bike around the garage. What an accident waiting to happen. I could not tell anything by visually checking like for car tires. Moto tires must have very stiff side walls. Well time to test it out again, but with normal tire pressures.
    Posted September 4th, 2013 at 09:31 AM by Lychee Lychee is offline
  3. Old Comment
    Lychee's Avatar
    A nail! Damned devil spikes!

    I guess the next uvas run is not going to be for awhile.
    Posted September 5th, 2013 at 01:47 PM by Lychee Lychee is offline
  4. Old Comment
    Lychee's Avatar
    Gone is the rear sport demon, in favor of a gt 501. Now just to find some time to ride.

    Adjusted rear preload to 2nd setting to adjust for rider sag.
    Posted September 11th, 2013 at 05:18 PM by Lychee Lychee is offline
    Updated September 13th, 2013 at 10:51 AM by Lychee
  5. Old Comment
    Lychee's Avatar
    Road Uvas yesterday. Unbelieveable. I love this bike.

    Now to save money to buy some held gloves, a new jacket, and some track time.
    Posted September 13th, 2013 at 10:50 AM by Lychee Lychee is offline
 

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