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  1. #1
    1946:2006:2066
    Reputation: FireDog46's Avatar
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    RM ETSX Head Angles Explained…

    To reiterate a previous post, one has to wonder what Rocky Mountain was smoking when they
    spec’d these bikes. The 2002’s and 2003’s came with a 100 mm fork and the geometry sheet
    listed the head angle as 71 degrees. The 2004’s come with a 125 mm fork and the geometry
    sheet lists the head angle as 70.5 degrees.

    The math doesn’t add up. A 125 mm fork should slacken the head angle by 1.2 degrees.

    Using high resolution digital images and a vector drawing program, these are my conclusions.

    Regardless of which fork is used, the head angle is .7 degrees steeper in the 4.5” travel setting.
    The 2002/03 listed head angle is for the 3.5”/4.0” travel settings. The head angle steepens to
    71.7 degrees in the 4.5” travel setting. The 2004 listed head angle is for the 4.5” travel setting
    and slackens to 69.8 degrees in the 3.5”/4.0” travel settings.

    .........3.5”/4.0”...4.5”
    2002/03..71..........71.7
    2004.....69.8........70.5


    With judicious use of rear and front sag one can balance the bike and compensate for the change
    in head angles. One recommendation I have heard ( not mentioned by any LBS I know of ) is to
    adjust the rear and front sag levels in the 4.0” travel setting. When you move to the 4.5” travel
    setting, the increased leverage ratio will increase the rear sag, compensating for the increased
    head angle.

    This is what I found myself doing intuitively when I first got mine. I was running about 30% sag
    in the rear and about 10% in the front. And never had a problem with handling in the 4.5” setting.
    It was when I converted to coil that the head angle discrepancies came to light. You can’t bleed
    a coil to get the right sag. I am waiting on a new set of springs for the rear since the 600# one
    I have now is too heavy for the 4.0” setting and could be just a touch softer for the 4.5” setting.

    To those considering an ETSX, don’t be put off by this information. The ETSX is one hell of a fine
    bike. I had been riding a GT LTS2 since 1996 and after a few years I started looking for a new
    bike…and kept going back to the GT. Nothing a tried was better. Then in 2002 I rode an ETSX.
    That was it. Bought it the next day. Have never looked back or at another bike.

    Does anyone know where I could get a hex bolt to replace that damn shock QR?

    michael

  2. #2
    1946:2006:2066
    Reputation: FireDog46's Avatar
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    followup...from the horse's mouth...

    I got a response from RM regarding ETSX head angles. The catalogue stated head angles
    are for a ladened bike, properly sagged rear and front, using the 4.0" travel setting. This
    applies to all model years. They acknowledge that the 4.5" steepens the head angle but
    keeping the same pressure/spring rate for the 4.0" setting, the increased leverage ratio will
    increase the rear sag, bring the head angle more or less back to normal.

    My previous post is accurate for an unladened bike without sag, and perhaps a little more
    useful in determing what head angle you would like to achieve by judicious use of front
    and rear sag.

    michael

  3. #3
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    Reputation: JoeDesperado's Avatar
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    does anybody know if RM changed the problem with the head angle getting steeper in the 4,5" (up to 2005) or the 5" (since 2006) travel mode?

  4. #4
    1946:2006:2066
    Reputation: FireDog46's Avatar
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    according to this post

    Quote Originally Posted by JoeDesperado
    does anybody know if RM changed the problem with the head angle getting steeper in the 4,5" (up to 2005) or the 5" (since 2006) travel mode?
    see http://forums.mtbr.com/showthread.ph...50056#poststop

    apparently was fixed for the 2006 models with the new linkage and shock for 4" - 5" travel.

    I'm also wondering why this thread didn't get moved to the Rocky Mountain forum.

    michael
    "Be not afraid of going slowly but only of standing still." - Chinese Proverb

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