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  1. #1
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    Fork Change - Will this screw up bike geometry?

    I am looking at swapping out my 80mm Manitou Axel Comp on my 2004 Trek Fuel 70 for a Marzocchi MX Pro Eta/Tas 100/120. How bad will this mess with the bikes geometry/steering. Is this a good idea? BTW...I mainly use the bike for adventure racing and training. So a lot of long up and downhills. Thanks.

  2. #2
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    Put a Talus RLC (80-130mm) On my fuel ex7 and did not notice too much of a difference, actually I like it more.

    I mainly ride XC with an All mountian tendency.

  3. #3
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    Thanks atenciole. What year is your ex7? and what were the original forks (size)?

  4. #4
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    It is an '06. It had a Reba SL. 100mm We al put my old Z.1 (130mm) on my buddies 2004 fuel 70. It is a good upgrade over the Judy that was on there and not too much of a geometry change.

  5. #5
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    Thanks again atenciole. I appreciate your help. Anyone else want to weigh in?

  6. #6
    Lionel Hutz, Esq.
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    A longer travel fork will make the head angle slightly slacker. Something like a degree difference per inch (I think). So you'll end up with something like a 1 deg slacker head angle - assuming you use the 100mm travel. That's not incredibly accurate, but that's not really the point here.

    A steeper head angle yields a more snappy ride. Easily steered and maneuvered, but twitchy and fairly unstable on descents. A slacker head angle is the opposite. Lazier steering but very stable.

    If you're doing a lot of long descents, it would probably help you to get a longer travel fork. However, you'll need to adjust to having more weight on the back end of the bike when climbing. If the steering is too sloppy, you could liven it up with a shorter stem (which would put even more weight rearward) or a narrower handlebar (more trouble than it's worth, in my opinion).

    Personally, I'd go for the 100mm unless I found myself running out of travel for a descent. Then again, I'm coming off a hardtail with 63mm of travel and now riding a full suspension with 130/120 front/rear travel.
    2007 Trek Fuel EX 8
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  7. #7
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    Quote Originally Posted by Dart77
    I am looking at swapping out my 80mm Manitou Axel Comp on my 2004 Trek Fuel 70 for a Marzocchi MX Pro Eta/Tas 100/120. How bad will this mess with the bikes geometry/steering. Is this a good idea? BTW...I mainly use the bike for adventure racing and training. So a lot of long up and downhills. Thanks.
    Dart - running the new fork at 100mm will slightly relax the geometry/handling, probably not a bad thing for your described use....running it at 120mm would possibly be excessive (I believe Trek recommends 105mm max travel on the Fuels, if I'm not mistaken. I'm not saying you can't/shouldn't run it at that length, just keep warranty considerations in mind if your frame fails - I believe 120mm exceeds the original design of the frame....tis up to you to decide)

  8. #8
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    What many people don't realize is that for every inch you go up in travel, the dropout to crown lenght is often 2 inch longer to accomodate the increased travel. I tried putting a vanilla 125mm on my fuel just to see what it was like, but it really screwed with the geometry. Then i dialled the fork down to 100 mm, which was much better, but the legs of the fork were still the same lenght and still an inch longer than my old manitou 100 mm fork.

  9. #9
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    One other consideration is that you should look at the axle-to-crown length of each fork, then subtract what kind of sag you usually set--i.e. 25% of travel.

    This will give you a more accurate idea of front-end travel change, rather than just measuring travel alone.

    But yeah, typically longer travel forks = longer axle-to-crown.

    One final note, as a precaution, make sure the axle-to-crown length on your new fork doesn't exceed the maximum that the mfr states can be used on your frame. Otherwise you might void the warranty.

  10. #10
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    Wow...all great info. I ended up going with the Reba Team at 100mm which I can set down to 85mm. I am running it at 100mm, at the moment, and it is not too bad. I notice it being a little looser on the steep uphills but, wow, what a difference that shock makes smoothing out the trails. And much more confidence going downhill. Again...thanks for all the help.

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