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  1. #1
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    Lefty tuning...

    I finally got my lefty with a Mendon Uber clamp on my 135mm offset 9:Zero:7 last weekend. I hastily set it up per Cannondale recommendations for preload for a race on Saturday and my main problem was with the tire hitting the crown rubbing the crown it's set currently for 100mm travel, but I only have 97mm between the crown and tire. It rubbed pretty frequently, particularly while braking, so I assumed that preload was insufficient. (I will have my frame machined and a lower stack headset installed to address that in the coming weeks and increase my clearance.) Apart from the rubbing, the performance was great, although there were some handling compromises from the added AC, cornering wasn't as precise as previously, but that was to be expected.

    I rode last night at my favorite neighborhood trails, (Belmont Plateau in Philadelphia) a very twisty and extremely technical system with punchy climbs, lots of logs, roots and rocks to negotiate, as well as a number of spots where, if you crash, you will likely get hurt. Per Craig/Mendon CycleSmith's advice, I set my pressure at -30# of my body weight. Compliance was much better and rubbing, all but eliminated, except under extreme circumstances. so far, so good. Problem: on several occasions, I had the front end wash out on me while cornering. Soil was not loose/notpacked with a little bit of organic surface debris. Almost hero dirt conditions, but not quite. Tire, Vee H-Billie @ 14 psi, on 65mm rims. (Never had it wash out with a rigid fork, previously.)

    95% certain that it comes down to 3 factors: geometry just added an extra 50mm to the AC, changing weight balance- perhaps I need to change body position while cornering & put more weight on top of the bike? too much preload, fork is not as compliant as it could be, leading to washing out in corners. (i'm not really buying this one, it is otherwise dialed pretty well.) Compression/Rebound damping is off: other than added preload, fork is exactly as it was set when I received it from XJaredX.

    Of the 3 factors, i'm leaning towards 1 & 3. I have quite a bit of experience with suspension from being involved in motorcycle roadracing for the past 10 years and know how much geometry and damping can affect handling. I'm pretty sure the preload is close. Geometry will be a matter of adaptation. that leaves damping. Does anyone have a recommended baseline setting for damping on the lefty?

  2. #2
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    14psi is too high imo.
    10 seems to be the sweet spot as far as tire staying solid, no squirm or self steer, but not too high to cause washing out.

  3. #3
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    I've been running at that pressure for years. it's not the pressure.

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    I weigh around 195#, Large 190, 9-0-7, Clownshoe and Bud, Lefty with 95 or so travel, rebound set in the middle, air pressure 75#, tire pressure 9psi, no rubs or wash outs.
    Do not adjust your fit. Put more weight on the front end in turns and trust it.

  5. #5
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    Quote Originally Posted by gcappy View Post
    I weigh around 195#, Large 190, 9-0-7, Clownshoe and Bud, Lefty with 95 or so travel, rebound set in the middle, air pressure 75#, tire pressure 9psi, no rubs or wash outs.
    Do not adjust your fit. Put more weight on the front end in turns and trust it.
    even with my stem flipped, my hands are 50mm higher from the axle than before. I think flat bars are needed. It definitely feels like there's not enough weight on the front, when leaned over, it feels like it just lifts off the ground

    I weigh in a bit above 260- i'm 6'8 and built like a defensive end, so my air pressures are set accordingly higher. 14psi probably translates to around 11-12 for the average sized rider, for me, it's firm, yet compliant and not bouncy. Much lower, -12psi) there's too much rolling resistance and the sidewalls feel they're folding over. with a 450mm fork, it stuck like velcro. Now, not so much.

  6. #6
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    Quote Originally Posted by Gigantic View Post
    even with my stem flipped, my hands are 50mm higher from the axle than before. I think flat bars are needed. It definitely feels like there's not enough weight on the front, when leaned over, it feels like it just lifts off the ground.
    Dropping your hand position 50mm is a drastic change in fit position! Your overall ride comfort and performance will likely suffer if you were (and I know you were), professionally fit. That will really tighten up your hip angle closing off your breathing more.

  7. #7
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    My main interest is getting back to my original fit numbers

  8. #8
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    I'd start by cranking the rebound to fully slow.

    Stock damper has 5 wt oil, you'd likely benefit from heavier weight at that sort of pressure.

    Cannondale damping is not turtle to rabbit, it's golden retriever to rabbit. So once you get a rider who's well over 200, and PSI set accordingly, you'll feel as though it has little effect on rebound at all.

    Full slow, dial it back from there, should it feel too slow (which I doubt).

    Otherwise, I'd agree, 50 mm up rise is a radical change in HTA as well as weight distribution.

    If you can tweak the head tube to make up the difference, cool, but were it me, I'd snap another spacer clip on, easier, quicker, and safe.

    Honestly, I'd consider shortening the fork a fair bit. No idea what it's set for, but I recommend the 500/90 set up for Muks and 907's, any longer and things get wonky, which, it sounds like, they are.
    This is a Pugs not some carbon wannabee pretzel wagon!!

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  9. #9
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    the HTA is now at 68, from 70. I went from 728mm of handlebar stack, pre lefty, to 770, after flipping my stem (just checked my measurements and fit docs) I can lose a spacer and drop another 10 mm and flat bars will drop me another 20. I ideally, I'd rather maximize the travel if I can, but if worse comes to worse, I'll put another spacer in there; I believe it's set for 100mm.

  10. #10
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    Quote Originally Posted by Gigantic View Post
    I'll put another spacer in there; I believe it's set for 100mm.
    If it has 3 spacer clips, it's either 110, or 90 (assuming the damper body is red not green).

    If you can shave the frame and get rid of interference, all good, but priority one is keeping your teeth in your mouth.....
    This is a Pugs not some carbon wannabee pretzel wagon!!

    - FrostyStruthers



    www.mendoncyclesmith.com

  11. #11
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    it has 3 and was rubbing on the crown with 95mm between the top of the tire and the crown, but i can't remember what color the damper body is. So, 110?

  12. #12
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    Or 90. Red damper can be set up either way, based on how long the upper SA piston is (you'd need the damper removed to see it).
    This is a Pugs not some carbon wannabee pretzel wagon!!

    - FrostyStruthers



    www.mendoncyclesmith.com

  13. #13
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    So... when i originally inflated the tires for a race 10 days ago, it was about 33... this week, it's been in the 50's and guess what? they expanded and i actually had +16psi in them... deflated them a few pounds and boom: velcro! I'm still not sure what damper it has, but i'm pretty sure the fork is set at 110mm, it has 3 spacers inside from what i can remember. Geometry is actually pretty nice- it does run a little wide while cornering, but it's manageable. because the head tube on the XL '12 907 135mm frame is obscenely long, the stanchion is 25mm lower in the bottom clamp than is ideal, but this means that it's not slacked out as much, meaning that it currently has the geo of a 90/80mm fork, with a 68 HTA, which on technical, rocky descents, is nearly perfect. I love this fork!

    I've managed to find the last crank brothers iodine headset in existence, which will lower the stack height between 2.5-5 mm and with any luck, I can get another 5-10 mm from machining the frame and position the stanchion in the lower clamp, closer to where it should go. i definitely want to drop my bars a little more, though, the front wheel gets really light on climbs. I'll be shopping for some carbon flat bars and maybe a steeper stem if that doesn't get me where I want to be.

    Craig, I'll give you a call later this week and order another spacer kit from you.

  14. #14
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    Nice!

    Is this a straight, or tapered head tube?

    Star headsets will have an even shorter stack, I want to say they are around 14mm total, I can be more accurate if that is helpful to you.

    Nice units, kinda fiddley to set up, but bomber once it's done. I'm running a few of them for tight fit situations.
    This is a Pugs not some carbon wannabee pretzel wagon!!

    - FrostyStruthers



    www.mendoncyclesmith.com

  15. #15
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    it's a straight head tube- the 2012's used 34mm tubes, so putting in a zero-stack head set isn't possible. I can't find anything about the Star Headsets, got a link?

  16. #16
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    found it, never mind

  17. #17
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    Huh, tire pressure eh?

    I've found you can't compare rigid to suspended, and even different rim width's. Glad you got it figured.

  18. #18
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    Quote Originally Posted by Gigantic View Post
    got a link?
    Euro Asia was/is(?) the supplier, you can call and get more info, but cannot order from them.

    Let me know if you need to do that, I'll get you squared away on it, and perhaps your local shop deals with hem too, no idea.

    Star 1 1/8" Threadless Headset - Euro-Asia Imports
    This is a Pugs not some carbon wannabee pretzel wagon!!

    - FrostyStruthers



    www.mendoncyclesmith.com

  19. #19
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    iirc, the stack n the iodine is around 16mm, hopefully it will suffice.

  20. #20
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    i'm getting close to having it optimally tuned. I took a spin at my local trails the morning and killed it without even trying. Wow, what a difference a shock makes on a fatbike!

    https://www.strava.com/activities/284075248

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