1. The most important thing about buying a new bike is to make sure it fits. The only way you'll know if the bike is right for you is to size up the bike and make sure that the bike's geometry matches your body's geometry. Ask questions and do some research.
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2. If possible, try to find a shop that will let you demo the bike on real dirt. Five minutes in a parking lot won't cut it. You wouldn't buy a car without a real world test drive, and a bike should be no different.
3. Don't belive the hype. Just because your favorite rider or best friend rides a certain bike, that doesn't mean that's the best one for you. Have an open mind and be realistic about your needs and ability.
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  1. #1
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    Specs for Fork Upgrade

    If I want to replace a suspension fork with a better one, what do I need to measure from the old fork to make sure I get one that fits? Steer tube I know is standard (this is a new bike). That about hub size, width, OA height, anything else I don't know about? Thanks!

  2. #2
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    The only three things.....

    you need to worry other than steerer tube diameter are, axel to crown height, steere tube length (if you are buying used), and the hub/dropout interface.

    Axel to Crown height is important in that if you end up with a fork that is say 1 1/2" longer from axel to crown than your original fork your handling and the rideability of the bike will suffer. Axel to crown height is measured from the top the crown to the center of the drop out. And it can vary quite widely from manufacturer to manufacturer for a given travel fork. AC height is affected by the forks travel as well. A 100mm fork will have a shorter AC height than a 130mm travel fork. So that would be one spec that should be compared between you current fork and any new fork you consider. General rule of thumb is to try and keep the AC height between the two forks at no more than + or - 20mm. This assumes you want to preserve the current ride and handling characteristics of the bike.

    Steerer tube lenght is a critical measurement if you are buying a used fork. You can always cut a steerer tube that is a bit long, but you can't add to it if it's too short! The best way to be safe with this measurement is to measure your current fork of course. Measure from the top of the crown up along the headtube of the frame to the top of the stem. That will be the steerer tube length that you'll need plus a few mm. Like I said before, you're much better off ending up with too much steerer tube than you need than you are with too little. As for a new fork this isn't an issue as manufacturers size their steerers extra long to begin with. And the idea is to cut them to fit a given frame, stem, and spacer combination.

    And finally the axel/drop out interface. There are currently three different sizes, two are through axel desings the third is the standard quick release set up. And none of them are compatable with the others. This is easy to figure out. If your bike uses a quick release hub then that's what you need for your fork, quick release drop outs, NOTHING esle will work. Then there is the 20mm through axel design, again if thats the type of hub you have you have to have a compatable fork. Then there is the new 15mm through axel. This one you likely won't have to worry about much as the design is just starting to become available and as of yet is not speced on a currently available production bike. To get an idea of what each of these looks like, just hit up any online retailer and look up their hubs or forks. You'll be able to easily tell the difference. As far as hub spacing, don't worry aobut it. Hub spacing is standard for quick release and 15mm through axel hubs at 100mm, and standard for 20mm through axel at 110mm. It is a VERY rare front hub that is speced otherwise.

    And just a side note: don't discount steerer tube diameter. You better make sure the fork you are getting is compatable. Granted the 1 1/8" steerer tube is the most common. But there are 1" (threaded and threadless) steerered forks, as well as 1.5" steerered forks floating around out there. So do keep that in mind. While 1 1/8 is certainly the most common, there are other "standards" out there that you might run into.

    Good Dirt
    "I do whatever my Rice Cripsies tell me to!"

  3. #3
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    Thanks, Squash. I was also wondering if there were any different angle or offsets. Not sure I am using the right terms, so I'll try to explain:

    Is the angle of the steer tube always parallel to the suspension axis? I could see the steerer being welded at some angle to give more rake, although this would quickly become a weak point.

    Is there a difference in the measurement (assume parrallel in part 1) between the steer tube axis and the shock axis? I know on my bike the steer tube sits 'behind' the shocks. Does this vary as well?

    Oh, and are all V brake system mounts the same or do I need to worry about that?

  4. #4
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    "Is the angle of the steer tube always parallel to the suspension axis? I could see the steerer being welded at some angle to give more rake, although this would quickly become a weak point."

    Yes the steerer and stanchions (upper tubes) and lowers are alway parallel. To set it up otherwise would cause binding problems and reduce the effecitveness of the suspension.

    "Is there a difference in the measurement (assume parrallel in part 1) between the steer tube axis and the shock axis? I know on my bike the steer tube sits 'behind' the shocks. Does this vary as well?"

    Not usually. This is called offset, and while it does vary somewhat, not usually to any great extent. You likely won't be able to tell the difference between one fork and another. If you take a look at any suspension for out there, the steerer tube is almost always offset to the rear of the axis of the fork legs. Even ridged forks have an offset. It's just accomplished differently in many cases than with a suspension fork. On many ridged forks the offset it accomplished by arcing the fork legs forward rather than the combination of forging a bend in the crown, and/or casting the drop outs a bit forward as is done with suspension forks. Anyway, it really isn't likey to be an issue at all.


    "Oh, and are all V brake system mounts the same or do I need to worry about that?"

    No worries there. Vbrake mounts (when present) are standard.

    Good Dirt
    "I do whatever my Rice Cripsies tell me to!"

  5. #5
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    Sweet, thank you! Great info!

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