Rigid Forks - 2 Questions- Mtbr.com
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  1. #1
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    Jul 2010

    Rigid Forks - 2 Questions

    Let me preface that this question is driven by my owning a Titanium Fat Bike, but I believe it is relevant for all platforms excepting rear suspended bikes.

    Question 1. Why do most, if not all, Titanium frame builders/manufacturers not offer titanium fork options with their frames. You always see carbon forks mounted on titanium frames. One would think that since one of the main virtues of titanium is compliance, a titanium fork would be one of the most useful areas when running full rigid.

    Question 2. Why are the rigid options almost always shorter from axle to crown than the corresponding suspension fork at 20% sag that the frame is designed around? Do rigid forks perform better with steeper head tube angles? If not, this makes no sense to me.

  2. #2
    pvd is offline
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    Jan 2006
    Most rigid forks are 'designed' by people that don't know the answers to your questions. You may need to dig a lot deeper.

  3. #3
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    Dec 2012
    I can answer your question #1 from personal experience with a 470mm ATC steel fork unicrown fork that I built for my plus bike and the fork that I built to replace it.

    You don't want flex (compliance) on a rigid MTB fork, if you ride in any sort of aggressive manner. That flex turns into a nightmare when trying to negotiate a bumpy downhill turn under braking. The fork legs flex backwards under hard braking until the front tire loses traction after hitting a bump, rock, root, etc. and then it rebounds forward. This process happens over and over causing a feeling that you don't have control of the front wheel and causing arm pump from trying to hold on and keep it going where you want it.

    To replace the unicrown fork, I built a faux truss fork similar to the Oddity Squidfork and there was no more skittering front tire, bucking bronco feeling on those hard braking downhill turns.

    There is a reason why Oddity and Jones make their Ti forks in the Truss or faux truss style.

    In response to your question # 2, frames are usually designed for a specific fork axle to crown and offset. Any other fork that you choose to put on it will be a compromise.

  4. #4
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    Jan 2004
    Titanium forks are notorious for cracking. This could be a shortcoming of the "designers" and/or their material sources. Should the truss forks show long-term survival rates then that may indicate that compliance and durability are mutually exclusive for titanium in this application.

  5. #5
    will rant for food
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    Jan 2010
    I figured the carbon forks thing was a question of molding simplicity. It's a single shape based more or less on a plane. That's about as easy as carbon molding really gets for a hollow shape.

    The idea of vertical compliance in a structure where it's just two sticks in between two points. That's not going to squish. Marketers can develop a persistent skin rash over this trope as far as I'm concerned. I think I probably believed it at one point. What a lie.
    Disclaimer: I run Regular Cycles (officialy in 2016, functionally in 2020).

  6. #6
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    Dec 2006
    Engineering wise the ďcomplianceĒ in titanium tubing is largely what you donít want in a fork, it will manifest in aft flex and spring like recovery under heavy braking. You will then get chatter/vibration and ultimately bad handling. Titanium is not best suited in a cantilever style application.

    Sales wise people buy Ti because itís light, carbon forks are light, so thatís the match. At least, thatís my take on it.

  7. #7
    Professional Crastinator
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    Jan 2006
    The Ti fork question has been answered.

    Carbon forks are generally available up to 490mm (with some possibly longer ones somewhere). That corresponds to a sagged 120mm sus. fork. On my fatbike, it works really well as it came with a 120mm Bluto. On many other fatbikes, I'm pretty sure it's too long.

    If you are talking about Motobecane, their steering geo. is not exactly set in stone. I'm pretty sure the longer the better, like 490mm.

    It's never easier - you just go faster.

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