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  1. #1
    "The Dude abides."
    Reputation: MBzip's Avatar
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    New question here. Geometry questions

    Well a coworker of mine just offered to build me a frame free of charge, and i obviously jumped on the offer. Unfortunately i don't know much about geometry so i had nothing to say when he asked what i might want. He suggested just using some tried and true bontrager geometry, which seems like a good idea, but i thought id ask anyway. What would you all wise SSers recommend for some XC geometry for someone with an aggresive riding style. Size wise im gonna go 18.5. I also have long arms but i like to ride fairly far bike. Im glad i have found someplace with people wiser then myself that i can nag about questions that are extremely uninteresting to respond to and actually get feedback. Thanks,
    Sam

  2. #2
    Out spokin'
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    Geometry 101

    Quote Originally Posted by MBzip
    What would you all wise SSers recommend for some XC geometry for someone with an aggresive riding style. Size wise im gonna go 18.5. I also have long arms but i like to ride fairly far bike. Sam
    Sam,

    I've been riding off-road for 19 years. I own two custom frames and have made the study of bike geometry a pastime to some degree. That doesn't mean that you'll like what I like, but I'll tell you anyway. It's someplace to start.

    I'll start at the back of the bike. I like short chainstays. Something in the 16" range. Short stays hook up better when you're out of the saddle and make the bike handle quicker. The framebuilding challenge is getting adquate tire clearance with very short stays. There's only so much room for chainrings, the chainstay and the tire.

    Think about which length cranks you'll use. If you plan on using 180s (or longer), make the bottom bracket higher. One common misconception about relatively high bottom brackets is that they raise your center of gravity so the bike won't handle as well. Not so. Everybody bends their knees. Five or ten millimeters won't matter one iota. I have several high BB bikes and they handle every bit as well, in some cases better, than my low BB bikes.

    I like a long top tube. I'm 6'3" tall and I like to stretch out. My XXL Vulture and Co-Motion custom frames have 25.5" top tubes. I'd rather run a long TT and short stem than the other way 'round.

    If you're utilizing long cranks, spec a steep seat angle. You want to maintain KOPS (Knee Over Pedal Spindle).

    Personally, I like quick handling bikes so I'll take a ~71 head angle. But some folks like 70 and still others like 72. Know your fork's axle to crown measurement in advance of building the frame.

    I like a steeply angled top tube and long seatpost. This makes the frame lighter and gives you some cush for your tush (with a boingy post).

    I'm sure there's more but that's about all I can think of right now.

    Enjoy your new frame.

    --Sparty
    disciplesofdirt.org

    We don't quit riding because we get old.
    We get old because we quit riding.

  3. #3
    Bikes not Bombs.....
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    Good comments Sparty....

    I agree with Sparty on the BB and most of the rest. Makes for a good handling bike. Keep in mind if you run a front shock to take into consideration the sag of the shock when compressed, i.e. when you jump on and start riding. This will often sag the front end of the bike 1/2 to 1 full degree. A compentent builder will ask what type of fork and travel you will be using and build accodingly.

    There is nother finer than a custom built ride.....except maybe two or three of them.....

    Best of luck on your new ride.

    JS
    Thanks to all of you for your friendships on this board..... -

  4. #4
    "The Dude abides."
    Reputation: MBzip's Avatar
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    Thanks

    thanks guys, thats given me some good direction, im gonna compare what youve said to notable ss builders too. The frame will be suspension corected, thanks for the reminder. Im excited, new frame at no cost makes johnny a happy boy. Thanks again
    - Sam

  5. #5
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    16" stays? damn, that's shorter than what my Imperial is running at the moment.

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