1. The most important thing about buying a new bike is to make sure it fits. The only way you'll know if the bike is right for you is to size up the bike and make sure that the bike's geometry matches your body's geometry. Ask questions and do some research.
mtn. biking 101
2. If possible, try to find a shop that will let you demo the bike on real dirt. Five minutes in a parking lot won't cut it. You wouldn't buy a car without a real world test drive, and a bike should be no different.
3. Don't belive the hype. Just because your favorite rider or best friend rides a certain bike, that doesn't mean that's the best one for you. Have an open mind and be realistic about your needs and ability.
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  1. #1
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    Cockpit length relative to a road/cross setup?

    I was given a 29er framset and some parts to help facilitate getting on the trails with friends of mine. most of my riding is done on a cross bike with a 53cm top tube and a 100mm stem. This fits me perfect, and I spend alot of time on the tops opf the bars, rather than the brake hoods, when just riding around.

    THe 29er has a 59.9 effective tt length, and has a ~120mm stem on it. I am alot more streched out (too the point where i can't support my upper body) and for the most part, my front wheel feels unweighted. Will a shorter stem fix alot of this problem? How much weight do I really want over the front end? What other factors am I missing here that I should consider?

  2. #2
    mtbr member
    Reputation: Kaba Klaus's Avatar
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    I can see that a 599mm TT plus a 120mm stem will stretch you out... In essence your MTB has a reach that is 89mm (530+100 - (599 + 120)) = 3.5' longer (horizontally) then your cross bike.

    This is a lot.

    Other considerations:

    - Width of the bar. MTB bars are typically wider than cross/road bars. A wider bar pull you out even further.
    - Sweep of the bar. Road bars are typically straight. MTB bars have up to 12 degree backsweep, moustache bars even more. Backsweep eliminates some streching out.
    - Vertical difference between seat and bar. The lower the bar, the more you get pulled out. A rising stem, spacers betwenn headset and stem, a riser bar can all be used to bring the bar up.

    Making up for 89mm sounds like a lot. Things you can try:

    The first thing would be a 60mm or a 80mm stem and potentially a more narrow bar. This will make a huge difference but might not be enough.

    A stem that rises, a bar with pronounced backsweep and or a riser bar come next. Hope is that lifting the cockpit eliminates the rest of the pull out factor.

    Playing with stem and bars also alters the handling of the bike. So you might end up with a bike that fits but doesn't feel good on the trail. So you better try before you buy. Either you get a professional fit session from a bike shop ($ service) or you hope to borrow parts from friends and play on your own. If you have a super bike shop you might be able to borrow components from them (old spares).
    "Lorem ipsum dolor sit amet, consectetuer adipiscing elit." - And I agree.

  3. #3
    Fat-tired Roadie
    Reputation: AndrwSwitch's Avatar
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    Quote Originally Posted by lordconqueror
    What other factors am I missing here that I should consider?
    A smaller frame?

    I'm anal retentive enough to have a file on my computer with measurements from my various bikes. I ride a 'cross bike with a 541mm top tube and 90mm stem and a mountain bike with a 590mm top tube and 90mm stem. My fast road bike has a 545mm top tube and a 100mm stem. You're trying to make up for a much bigger difference in size, and it doesn't sound like your 'cross bike really fits you to begin with - the hoods position should really be the most comfortable spot, at least if you're pedaling at your normal cadence.

    Looks like while I was clicking "reply," Kaba wrote a post covering most of the same material.

    Before you go to the time and expense of building up your 29er frame, consider buying a frame yourself. Go to some bike shops and test ride some mountain bikes, so you can figure out a good top tube length and reach for you, and get a frame to match that. Have you been off-road on your 'cross bike?
    "Don't buy upgrades; ride up grades." -Eddy Merckx

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