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  1. #1
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    Gary Fisher Cobia question

    Looking at getting a used GF Cobia.

    The bike has normal wear around most parts, however, noticed 2 issues.

    1. Cosmetic- The chainstay has quite a bit of wear/rubbing around where the front largest chain ring seems to have rubbed it. While there is no contact between the frame and the chain ring during normal condition, could this be a sign of more than natural flex in the frame leading to rubbing while riding?

    2. Functional - When exerting force on the pedals, the chains slips, is very evident on the 8th and 9th gear.

    Is this typical of used bikes, or should I be weary?

  2. #2
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    1. Probably NOT the chain ring. Probably chainsuck, dropping off or possibly chain slap although chainslap usually is not so close to the chainrings. The chainstay also often gets rubbed by the rider's heel that wipes off paint.

    2. Drivetrains wear out. If you can borrow the bike and take it to a shop for checking out it might be a good idea.

    The chain stretches over time / rollers and pins wear as do the teeth in the chainrings and cassette and the rear derailleur cogs. Typically you replace the chain once or twice a season. Skipping is often caused by worn chainrings holding onto the chain beyond where it should release and then dropping off unexpectedly. Depending on how much you ride, what components you use and how you ride and shift you can go through cassettes once a season or three and chainrings may last two or three seasons. I went through my first set of chainrings after 3 years and replaced the cassette although it gauged ok. One of my buds rides a lot more but more smooth terrain and he is just replaced his chainrings on his 4+ year old bike. Skipping on the rear may mean the rear derailleur just needs adjustment or it may mean the derailleur hanger (~$15 part) or rear deraileur is bent.

    Cassettes:
    http://www.pricepoint.com/thumb/3-Pa...ettes-True.htm
    Year models mean next to nothing on parts:
    http://www.pricepoint.com/detail/129...sette-2009.htm

    Chainrings:
    http://www.pricepoint.com/thumb/3-Pa...uards-True.htm
    These are the ones I installed on my last bike:
    http://www.pricepoint.com/detail/163...-Rings-Set.htm

    Chains:
    http://www.pricepoint.com/thumb/3-Pa...hains-True.htm
    SRAM 971 or 991 seems to work well, avoid hollowpin IMO.

    Rear Derailleurs
    http://www.pricepoint.com/thumb/3-Pa...leurs-True.htm

    The bike might need an inexpensive tune or it might need some parts replaced.
    On my hardtail I have a N-Gear jumpstop to help prevent the chain from dropping off and typically use a lizard skin chainstay protector although wrapping with an innertube might be slightly more bulletproof.

  3. #3
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    Appreciate the answer and recommendations archer. I'll try and get it checked out at the LBS. Hopefully, its just the chain or some minor tuning.

    Also will post a picture of the wear spot just to confirm what you think it may be. The are of the rub is directly under the large chainring, so not sure if the foot rubbing can cause it unless the foot is rubbing against the chainring causing it to leave the scratches on the stay.

  4. #4
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    Usually the foot rubbing is going to be in the middle of the stay.

    I'm guessing here...
    Right at the chainrings, where the big ring is closest to the stay is possibly chainsuck or a worn chainring. The chain dropping off the chainrings will probably score the bottom bracket.

    Chainsuck can be minimized by a clean drivetrain that's adjusted right and possibly the Jumpstop I mentioned. I had some with my Big Sur right after I got it but with a little tweaking and keeping it reasonably clean it went away.

    I had a worn middle ring that caused skipping under load. As the chainring wears it forms little hooks on the teeth. The hooks hold onto the chain and it starts to go up the backside of the ring until the tension pulls it loose. I guess it might continue until it hit the chainstay near the ring if it was bad enough. I replaced the rings as I said above and have zero complaints with the new parts. I could have replace just the one ring but decided to change the whole ball of wax at one time.

  5. #5
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    Quote Originally Posted by archer
    Usually the foot rubbing is going to be in the middle of the stay.

    I'm guessing here...
    Right at the chainrings, where the big ring is closest to the stay is possibly chainsuck or a worn chainring. The chain dropping off the chainrings will probably score the bottom bracket.

    Chainsuck can be minimized by a clean drivetrain that's adjusted right and possibly the Jumpstop I mentioned. I had some with my Big Sur right after I got it but with a little tweaking and keeping it reasonably clean it went away.

    I had a worn middle ring that caused skipping under load. As the chainring wears it forms little hooks on the teeth. The hooks hold onto the chain and it starts to go up the backside of the ring until the tension pulls it loose. I guess it might continue until it hit the chainstay near the ring if it was bad enough. I replaced the rings as I said above and have zero complaints with the new parts. I could have replace just the one ring but decided to change the whole ball of wax at one time.

    Heres a shot that may help explain where I'm seeing the damage. The highlighted area just under the largest chain ring...
    Attached Images Attached Images  
    Last edited by Giskarded; 06-09-2010 at 04:20 PM. Reason: adding image

  6. #6
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    Probably chainsuck. The skipping might be related.

    Clean drivetrain, make sure the chain and chainrings are not worn out replacing components as required, shift the front rings before you are under heavy load and rely on the rear shifting when climbing.

    http://www.fagan.co.za/Bikes/Csuck/

    http://www.gvtc.com/~ngear/chainsuck.html

    http://www.sheldonbrown.com/gloss_ch.html

    http://www.ehow.com/how_14193_avoid-chain-suck.html

  7. #7
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    Just checked and this is pretty much what it looks like.. only worse.



    Have been warned that Trek will not warranty due to chain suck damage

  8. #8
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    Actually Trek won't warranty due to second owner.

    As for chain suck damage, they might consider that the same as a crash or normal wear and tear especially on an older bike.
    My Big Sur pretty much stopped sucking chain after the first few rides so I suspect the origional rings might have been burred a little or the chain stiff.

  9. #9
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    This lines of Gary Fisher frames are notorious for chainsuck. I'm a fanatic with my bikes and clean the drivetrain/chain after every ride. In odd conditions, changing from granny ring to middle ring will cause chainsuck. Trek dealer said the only thing I can do is put a smaller middle ring, or a wider bottom bracket to get the chainrings away from the chainstay since it is such a tight fit. Backpedaling to situate feet also causes chainsuck cluster****s on this class of frames from what I hear.

    All I know is that it is a design flaw that Trek isn't willing to accurately call a flaw, just so they could have a few more mm width on the chainstays, Shameful.

  10. #10
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    Actually while there is a reputation for chainsuck problems I've not found that to be overblown.

    I had a little chainsuck when the bike was new but got pretty good at adjusting the deraileurs and cleaning the drivetrain every couple or three rides.
    I also added a N-gear jumpstop and although I've dropped a chain maybe twice in four years on that bike had no real additional problems. The only REAL recurring chainsuck problems I had was when the middle ring was worn completely out. Putting new chainrings on the bike (same size with the same number of teeth) and in the year and a half I rode it after that I had no chainsuck problems.

    Four riding buddys with Fisher hardtails and no real reports of chainsuck issues.
    I'm not saying you aren't having a problem but nororious may be too strong a word.

  11. #11
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    Quote Originally Posted by archer
    Actually while there is a reputation for chainsuck problems I've not found that to be overblown.

    I had a little chainsuck when the bike was new but got pretty good at adjusting the deraileurs and cleaning the drivetrain every couple or three rides.
    I also added a N-gear jumpstop and although I've dropped a chain maybe twice in four years on that bike had no real additional problems. The only REAL recurring chainsuck problems I had was when the middle ring was worn completely out. Putting new chainrings on the bike (same size with the same number of teeth) and in the year and a half I rode it after that I had no chainsuck problems.

    Four riding buddys with Fisher hardtails and no real reports of chainsuck issues.
    I'm not saying you aren't having a problem but nororious may be too strong a word.
    I would be very very happy to believe that I am the exception, and quite possibly wrong. My previous post was sort of rage motivated too. I still believe the >4mm should have been addressed with the bike in design stage. (Superfly has Trek addon rub plates to prevent carbon-wear in this area, I use a glued piece of beer can.)

  12. #12
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    Another Cobia quiestion...

    I bought a 2007 cobia when I was getting back into riding. I still love the bike but I'd love to drop some of the weight... I don't really just want to turn it into a Paragon becasue I feel like that would cost me more than needs be. Where will I get the most bang for my buck to drop some of the 31 lbs?

  13. #13
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    Quote Originally Posted by lalahsghost
    I would be very very happy to believe that I am the exception, and quite possibly wrong. My previous post was sort of rage motivated too. I still believe the >4mm should have been addressed with the bike in design stage. (Superfly has Trek addon rub plates to prevent carbon-wear in this area, I use a glued piece of beer can.)
    I can relate to your frustration.
    Been there done that with a lot of other stuff over the years.

  14. #14
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    I had the same problem with my 2010 Cobia till I upgraded to all 2x10 x7 components. Now it is extremely rare to have a chain issue. However, I would upgrade bikes instead if I had to do it again.
    2012 Stumpjumper FSR Expert Carbon 29er

  15. #15
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    I still own mine, and don't enjoy it. I don't know whether it is the bike, or the riding conditions in my area. I don't want to lay tons of cash into this thing, but at the same time I'm worried that I'll still end up not enjoy riding the local ATV trails if I get a new bike. (seriously, 26201 is a sad place for MTB)

    I guess I have a pretty conflicted relationship with my MTB...

  16. #16
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    Smile

    Quote Originally Posted by lalahsghost View Post
    I still own mine, and don't enjoy it. I don't know whether it is the bike, or the riding conditions in my area. I don't want to lay tons of cash into this thing, but at the same time I'm worried that I'll still end up not enjoy riding the local ATV trails if I get a new bike. (seriously, 26201 is a sad place for MTB)

    I guess I have a pretty conflicted relationship with my MTB...
    What causes you to not enjoy it? The only time I didn't enjoy mine was while I had all the mechanical issues. Perhaps if it is working good you might consider upgrading to a full suspension. I did that and now I like riding even more. It makes riding more comfortable for me.

    Never rode out there but have heard the east coast is great for MTB. Maybe not exactly where you are, but maybe if you did some weekend road trips to some better trails you might find your pleasure there. Our trails here in eastern NE are OK, but I also must travel for the really good ones. So far the Black Hills in SD has been the best but KS has some really good ones as well.

    If I had to do my Cobia over again I would not have upgraded its components, I would have upgraded to a better bike. Search Pinkbike.com and craigslist and even ebay for a good deal on a used bike. Also the local bike stores might have classifieds to search.

    Hope that helps somehow.
    2012 Stumpjumper FSR Expert Carbon 29er

  17. #17
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    Quote Originally Posted by Stumpy12 View Post
    I had the same problem with my 2010 Cobia till I upgraded to all 2x10 x7 components. Now it is extremely rare to have a chain issue. However, I would upgrade bikes instead if I had to do it again.
    When you did the upgrade, which front der did you get? I've read the few comments that a high mount 34.9 wont fit on these frames. Any help would be appreciated!

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