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  1. #1
    MountainGoat aka OldGoat
    Reputation: pachaven's Avatar
    Join Date
    Dec 2005

    HD Effective Top Tube

    I'm looking at the HD and was in the ibis site and noticed that the ETT changes depending on the fork. If you go from 160mm fork to 180mm you lift the front end. But the ST should move also??? Why is that?
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  2. #2
    mtbr member
    Join Date
    Oct 2008
    I asked this question back in the beginning when the specs came out.

    From what I understand, the ETT is measured horizontally (parallel with the ground) from the center of headtube to the center of seat tube. With a longer fork, the headtube height moves up and so does the horizontal line used to measure the ETT. For the seat tube to intersect the horizontal ETT line, it gets extended upwards at the new angle of the seattube. The increased headtube height and slacker seattube create an overall longer "effective" top tube. Its pretty clear once you understand how the ETT is measured.

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