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  1. #1
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    Question for BMC Fourstroke owners ....

    I recently purchased an '08 Fourstroke with the DT Swiss XM180 shock on it. Very pleased with the quality of the frame, and the bike built up quite nicely.

    One thing I am not sure about is the amount of shock movement I get while spinning (yes, consciously spinning smoothly) on flat pavement. Is the shock movement normal? Seems to move about 5-10 mm per pedal stroke.

    I have the shock set at 20% sag ( I weigh 170, with 100 lbs PSI in the shock), and the rebound set 9 clicks from slowest setting.

    On the trail I am getting about 65% travel based on the o-ring. Would like to drop the PSI to get more travel, but don't want more pedal induced movement.

  2. #2
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    When you are pedaling on flat ground and spinning, it will bob a bit. But when you are going up an incline, the bob get's minimized due to the linkage design.
    I wouldn't worry about the bob unless you notice that it's sucking power from your strokes.
    I notice that my pedaling is more efficient when I have lockout on (Manitou Radium R), but a sore ass is worse.

  3. #3
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    Thanks. I guess I am just going to have to keep making adjustments to the shock. I don't feel 'much' power loss pedaling on the trail, but then again, I am only using 65% travel. And for some reason it bothers me that it bounces up and down, when I've had plusher FS bikes (Turner Flux for one) that didn't bob at all.
    I can't help but wonder how a Fox RP23 or RP3 would affect the linkage movement while pedaling.

    I've included a photo of the build.
    Attached Images Attached Images

  4. #4
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    Hmm, when mine bobs, I can't really feel it, but if I look down, I can see the linkage move a bit up and down.

    A platform shock on this bike would work the same as on any other bike. It will stop it from bobbing in the initial part of the stroke.

  5. #5
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    Hey Morgan, I just built up a 2008 Fourstroke about a month ago. I notice tons of bob on mine. I'm about 180 lbs, and have about 110 psi in the rear shock. I'm often finding myself locking it out when climbing up long climbs on fire roads. I do like the way it climbs over rough terrain, though, when it's in plush mode.

    This is my first FSR, though. So maybe I'm expecting too much.

  6. #6
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    Quote Originally Posted by taudep
    Hey Morgan, I just built up a 2008 Fourstroke about a month ago. I notice tons of bob on mine. I'm about 180 lbs, and have about 110 psi in the rear shock. I'm often finding myself locking it out when climbing up long climbs on fire roads. I do like the way it climbs over rough terrain, though, when it's in plush mode.

    This is my first FSR, though. So maybe I'm expecting too much.

    No - you are not expecting too much. I've owned several FS bikes, and this is the first one I've experienced pedal bob on, while doing a smooth spin on a flat road, and I even get it cruising downhill. I'm okay with linkage movement when I am standing and mashing on the pedals - as this is normal and expected.

    I agree with your statement about the bike climbing rough terrain - that has been the bright spot so far.

    I'm about 170 lbs, and have been running 100 psi, so it sounds like we are running about the same sag. How much travel (based on the o-ring) are you getting?

    I contacted BMC, and they blew me off and referred me to DT Swiss, saying it must be a shock issue. DT Swiss has not yet responded to my emails or phone calls, but it's only been 4-5 days. I'll keep updating this thread as things progress.

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    I'm at about 20% sage. I haven't really messed with the rebound setting too much yet. I'll stay tuned to hear about what you learn.

    Edit: I'll add that I notice that they have a remote lockout for this shock, I wonder if it's really designed about having to manually control it's ride? Reading the marketing material at the dt swiss site about the 180 XM, it sort of sounds like maybe you do? The DT Swiss information: DT Swiss 180 XM

  8. #8
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    Don't bother calling DT,

    What you are experiencing is normal for that bike.
    Some people prefer to tolerate a bit of bob in exchange for a very supple suspension, others want a stiffer ride, so get one of the Propedal Foxes.

    I ride a trailfox, same bike with 4.75" of rear travel, DT shock. It rides like yours, a bit of linkage movement, but pedalling, can be as agressive as a regular XC bike.

  9. #9
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    Quote Originally Posted by Pedro
    What you are experiencing is normal for that bike.
    Some people prefer to tolerate a bit of bob in exchange for a very supple suspension, others want a stiffer ride, so get one of the Propedal Foxes.

    I ride a trailfox, same bike with 4.75" of rear travel, DT shock. It rides like yours, a bit of linkage movement, but pedalling, can be as agressive as a regular XC bike.

    I agree that it still pedals well when attacking a hill. The thing that gets me, is I'm only getting 60% travel, and still have tons of linkage movement when doing an easy spin. When I adjust the sag to 25% to get closer to 85-90% travel, the amount of linkage movement when spinning on a flat road is comical. My riding buddies look at it, smile and shake their heads.

  10. #10
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    Take your air pump with you on your next ride and fine tune your sag for the best compromise between travel and linkage movement. I remember reading these type of rear suspensions (DW link type) are very sag sensitive.

    Ïf your bike is not getting 100 percent travel, but you like the travel you are getting, dont concern yourself with that but rather enjoy your ride, until your next frame upgrade time.

    Tell your buddies to stop being wimps and take them to a very gnarly, rocky trail. They won't be able to see you smilling and shaking your head at their stiff end rides, they'll be so far behind you. Then your fourstroke's behavior will start to make sense.

    Before you think about swapping frames, try a fox rp23 shock

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    @Pedro. Thought never crossed my mind about switching frames, thought about getting a different rear shock, though. Anyway, good advice about fine tuning sag. Talking with guy at LBS who rides a similar setup, he's running at almost 40 pounds higher pressure than what DT Swiss suggests for his weight...so I've been adding more and more air to mine to find the ride I like. And now I know not to be shy about throwing 130 to 140 in there.

  12. #12
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    Semi hijack here: I have the sameish problem, only the other way around...

    When riding with the rear shock locked out on pavement or smooth gravel it feels like I am riding a huge egg shaped wheel even if I try to spin smooth. But when I open the shock I feel no bobbing. It looks like I have the same movement in the linkage, but I donīt bob.

    Right now it is set up with 100 psi, and I love the plush feeling when riding rough trails, and that I do not bob at all when riding it open on smooth terrain. Have tried 120psi, but had the same bob, only a bit harsher when riding it open over rough terrain.

    Does not seem like a big issue, but on most of my rides I have long climbs on pavement that consists of a lot of small hills that I normally just power up out of the saddle, and it is annoying to open the shock for the flat pavement in between the small hills.

    Anyone have an idea about what to do? Donīt think I can tune it out, since it is in the locked out mode I am having issues.

    TIA
    Tori

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