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  1. #1
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    Back pain issues & DJ sizing questions

    I just bought the Diamondback 2nd assault last week, which is my first DJ bike and seem to be having some issues with lower back pain after riding. I'm about 6'1" 165lbs, prior to this I had the Giant Rincon which fufilled most my needs but I was looking for something a little lighter I could toss around more.

    I'm worried that the bike might be too small because after riding i'm left with sharp, shooting pains in my lower back. When i'm pedaling my knees almost hit the bars and when im standing with the pedals at an equal horizontal I definitely have to reach down far to grab the bars.

    Is there anything I can do to the bike or could do myself to help with this? I just want to figure it out as soon as possible so I can bring the bike back for something a little bigger if I have to.

  2. #2
    pnj
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    I think they only have one size of this frame? 22 inch top tube.

    I suggest taller bars and a longer stem and do some stretching before/after you ride.

    I know their team rider is 6'7" or something.

    If you're new to riding this type of bike, even if it fits you, your muscles aren't used to being used in the riding position so they'll get sore.

  3. #3
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    that bike appears to have pretty low bars. taller bars will help. the website below says they are 31.8 clamp area, so be sure to check for that. Atomlab makes a 3" rise bar with 31.8mm clamp area.

    3 inch rise bars 31.8mm clamp diameter



    Diamondback Bicycles - 2nd Assault

  4. #4
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    How long of a top tube did you like on your trail bike? 22" TT seems too small for a 6'1" guy.

    The tall bars will be a bandaid if the bike is just too small for you.

  5. #5
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    I'm 6'1", and I ride a 22.5"tt (that's actual tt measured from center of seat tube to center of head tube ... not "effective" top tube.

    22" effective would be short. But 22" actual is a Medium. My old DJ bike had a 22"tt and I liked it fine (although I did end up running a 70mm stem for more room).

    I have low back issues myself. If you have shooting pains, or any numbness in your leg/toes, def get it checked out. You could have a herniated disc.

  6. #6
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    Quote Originally Posted by GTscoob View Post
    How long of a top tube did you like on your trail bike? 22" TT seems too small for a 6'1" guy.

    The tall bars will be a bandaid if the bike is just too small for you.
    Mesasured it last night and it seems to be around 23'

  7. #7
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    I'm 6'5" and ride with a 22.2" TT. I rode it the first time yesterday, I do feel my lower back a bit but not that much. 2 weeks ago I rode at a bike park with a medium rental DH bike, my back ached for a week. Conclusion: I think 23' should be ok?

  8. #8
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    Quote Originally Posted by dfuse View Post
    I'm 6'5" and ride with a 22.2" TT. I rode it the first time yesterday, I do feel my lower back a bit but not that much. 2 weeks ago I rode at a bike park with a medium rental DH bike, my back ached for a week. Conclusion: I think 23' should be ok?
    Yeah, plus raise your handlebars. Many DH bikes are set up with zero or minimal rise bars--even the size L ones, which I think is dumb. Why would the S,M,and L all have the same height bars? More for looks than bike fit.

  9. #9
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    Yeah since I rented the bike I couldn't really change the bars and I think the fact that it was a medium didn't help a lot either.
    I am considering risers bars on my dj bike after reading this thread though, my current bars only have a very small rise.

  10. #10
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    Quote Originally Posted by dfuse View Post
    Yeah since I rented the bike I couldn't really change the bars and I think the fact that it was a medium didn't help a lot either.
    I am considering risers bars on my dj bike after reading this thread though, my current bars only have a very small rise.
    I've run into that issue before, on trips to mountains and riding rental DH bikes. I've actually discovered that sometimes the Medium works better, when both the M and the L have low bars. The reason is that leaning out and down is worse for the low back than having the bars close and low. Also, I noticed that getting my stance behind the bottom bracket (even more than on my DJ) is good for DH (when the bike is angled down steep rough sections). And it also seems to help with jumping, because I pre-load the suspension with my stance behind the bottom bracket even more than normal. I don't own a DH bike, but these are some of the ones I have ridden as rentals:

    Kona Operator


    Trek Session 8


    Scott Voltage FR 10


    another Scott Voltage:


    Also have ridden the Specialized Demo 8. The only one I can say I honestly do not like is the Kona Operator. The others are rad bikes. The Scott feels the most nimble for jumping.

  11. #11
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    This is the bike that was available at my (very small) bike park:
    Back pain issues & DJ sizing questions-8544.jpg
    Can't compare though, it was my first try at DH. I sucked big time, and that's why I bought a secondhand DJ/4x bike (Dialled Holeshot) to practice jumping first.

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