Steering Geometry Anyone?-
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  1. #1
    Professional Crastinator
    Reputation: Fleas's Avatar
    Join Date
    Jan 2006

    Steering Geometry Anyone?

    I figured this group might be able to put meaning to some random numbers.

    I am trying to compare bikes.
    I have done my best to measure and calculate head angle and steering trail.
    Rigid forks on both.

    I noticed that one bike seems to handle skinnies better (trail ~108mm, HA 68.5*, wheelbase=1144mm). The other bike corners better (trail ~98mm, HA 69+*, WB=1095mm). I rode them back to back to back several times, and the "skinnies bike" seems to like to go straight and seems to require a little more steering effort away from center. The "cornering bike" feels slightly unstable on-center, but almost takes a set with very little steering input when it's leaned over in a turn and just carves.
    I like doing skinnies, but I like the cornering bike better for all-around riding so I am swapping in an external lower headset race for the zero-stack that's currently in there. That should bring the HA and trail to around the same as the "skinnies bike", but still with a shorter wheelbase. I am expecting the steering to "slow down" a tiny bit.

    Do these trail numbers sound right? Does it sound like the numbers jive with what I think I'm experiencing and expecting in handling? The bikes are fairly recent models - not old, steep-angled XC rigs.


    It's never easier - you just go faster.

  2. #2
    Moderator Moderator
    Reputation: Walt's Avatar
    Join Date
    Jan 2004
    Too many other variables involved to say anything certain. And the feelings you're describing are fairly subjective, too. Welcome to the magical (sometimes infuriating) world of bikes...


  3. #3
    Professional Crastinator
    Reputation: Fleas's Avatar
    Join Date
    Jan 2006
    New external lower cup installed and parking lot tested. It seems to have made only a very tiny difference. The bike seems less twitchy on-center. Probably the more noticeable thing is that when turning sharply, the front doesn't seem to want to dig/tuck/oversteer. That's a cool feeling.
    So, I didn't lose, but the "win" is barely perceptable. I'd guess chainstay and/or wheelbase might have a greater impact, so maybe I'll slide the rear axle back and see how that feels.

    It's never easier - you just go faster.

  4. #4
    mtbr member
    Reputation: Eric Malcolm's Avatar
    Join Date
    Dec 2011
    Wow, I keep coming back to this thread and think 108 and 98mm trail.
    You know, I started my cycling Road race career on bikes with only half those figures. And with wheel-bases under 1000mm - we thought we were cool. This was on the road so it is a different environment. I mention it only as a pointer to the progress being made today. Also of note is the motorcycles that I rode in the 1970's used similar trail that you mention. Progress.
    My own bike has 82mm and I feel that this is favoring to the under-steer end of the spectrum. Maybe there is a new 'normal' for MTB that is more akin to MX motorcycles than a 'bike'. I would analyse the numbers given by the OP to offer a heavy to steer bike in both forms that is inclined to track in the straight ahead with a solid running on rails feel. Steering is by the use of wide H/Bars for leverage and if you are to ride down a trail requiring a quick left to right to left rapid directional change the bike wants to run straight ahead. Body language and some force makes the bike turn. As Walt said, welcome to the world of bikes....

    If I don't make an attempt, how will I know if it will work?

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