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  1. #1
    mtbr member
    Join Date
    Feb 2011

    100 v 125 mm Fork / Geometry

    Hey guys, I ride a 2004 Specialized Hardrock which I've been upgrading quite a bit. I currently have a Fox Vanilla R fork on it set up at 100mm travel. I am going to pull it to do the seals / oil and am considering increasing the travel to 125mm since it is internally adjustable. The head angle is currently 70 degrees with a 100mm fork, and the frame is rated for up to a 140mm, so no worries about strength.

    I mostly ride flowing, equal up and down, rooty trails, and have been getting a bit more aggressive lately with natural jumps and drops, etc. I am wondering if I lengthen the fork, what effects it will have on the bike. It would be nice to raise the BB slightly since do often have problems with pedal strike on tall roots and logs, I know that is a product of timing the cranks but sometimes it is unavoidable. Also when landing small jumps at speed the bike feels a little twitchy and I was hoping slackening it out a bit would help that. I do a decent amount of climbing though as well as tight, winding trails, and don't want to lose out there, and I don't often bottom the fork, suggesting that I don't really need an extra inch of travel.

    Any opinions if I am going to like it or not? I know I can always try it and then swap it back if I dislike it, but it is a decent amount of work so I'm trying to figure it out up front. Thanks!

  2. #2
    Picture Unrelated
    Reputation: zebrahum's Avatar
    Join Date
    Jun 2005
    Where did you get that the frame is rated to 140mm? That sounds suspect.

    Your bike with 125mm is going to ride like a tractor, if the headtube is rated to 140 then you should probably give it a try just so you know. You might like it or you might not, it's a personal preference thing. My bike is pretty unusual to ride with 15mm travel increase, I'm not sure I would suggest it to most people but it works.

    Travel adjust on a Vanilla isn't too hard so don't be stressed about changing it back and forth.
    Don't you hate it when a sentence doesn't end the way you think it octopus?

  3. #3
    mtbr member
    Join Date
    Jan 2004
    Is that 140mm rating from a reputable source? I agree with zebrahum that sounds fishy. Especially because 140mm was not a standard travel rating for that year. At that point most forks were 80/100/125. I believe 2007 was the first year Fox did 140mm for their normal Float/TALAS/Vanilla lineup. I think RockShox was somewhere around the same time.

    As a general rule of thumb 25mm of axle to crown height will equal 1 degree of head angle. So assume you go to 125mm from 100mm it will:

    * Slacken head angle by 1 degree. The result of the slacker head angle will increase the bike's trail measurement slowing down steering but making it track better.
    * Increase bottom bracket height by about half an inch
    * Relax seat tube angle by 1 degree moving you further behind the pedals

    This is just to give you an idea. Obviously it is going to change all the measurements. There are some smart folks at Specialized who figure all this stuff out. Personally, I've found that most bikes ride better using the recommended settings. How did I figure that out? Trying stuff that wasn't one of the recommended settings. Anyway, just some food for thought.

  4. #4
    mtbr member
    Join Date
    Feb 2011
    Just giving an update after a few rides in case anyone else is considering switching up their bike. Going from 100mm to 125mm fork travel made a HUGE difference, almost completely for the better IMO.

    It shifted my weight rearward, slackened the head angle noticeably, and raised the BB height. All of this together made the bike a ton more fun to ride and playful, much easier to lift the front end off the ground, and so much more confident and planted on downhills and jumps. Technical uphill climbs are actually easier as well, as shifting the weight back helps maintain traction, and the rearward weight shift and higher BB height lets me plow and spin straight up very rooty climbs that used to require more finesse.

    The only negative change I encountered was a bit less steering precision when seated on very tight switchbacks, it's not a big problem and when standing up with a bit more weight on the bars it isn't noticeable at all.

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