Reduce Fork Travel

Forums Mountain Bike Forum Reduce Fork Travel

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This topic contains 6 replies, has 4 voices, and was last updated by  comacruz 8 years ago.

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  • #103610

    Hi All,

    New to forum – appreciate suggestions and answers. Background is road / cyclocross racing -mostly pack fodder in the 30+ races I do per year but although I do get lucky every now and then with a W – usually when all the strong guys are riding a bigger event 😃 Pretty new to the MTB scene but it should suit my skills once I learn how to ride handle this big bike.

    Recently purchased a Niner A9C – sweet ride but having some fit issues as handlebars are sitting about 2 inches higher than seat with fork locked out – less when fork is open and some sag but still some rise. Small frame (I’m 5’5) with flat bars slammed (no spacers) and negative 20 degree stem on there. Fork is a 2011 Fox 32 Float 29 100 FIT RLC 15QR. I’ve ridden it for about 3 months hoping to "get used to it" but the reality is the front end needs to come down more.

    Will the Axle to Crown length be reduced by 20mm if I convert the 100mm fork to an 80? Will it effect the spring rate? I’ve scoured the internet and seem to get conflicting answers. Any suggestions?

  • #103611

    Yes, if you reduce the travel 20mm, then the A2C will drop 20mm correspondingly.

    As to your second question. Typically, an air fork achieves travel decrease/increase with the addition/removal of spacers on the air spring assembly, respectively. This effectively will reduce the air chamber size (travel decrease, spacer added) or increase the air chamber size (travel increase, spacer removed). This has several effects. The most pronounced effect is the increase in preload for a given spring pressure. This is also an easy fix. You can reduce the pressure in the chamber to get the preload you desire. The change in the air chamber size also effects the spring rate somewhat. A reduced air chamber tends to have a more progressive rate, versus a more linear rate for a larger chamber. This, unfortunately, can’t be tuned out easily (although fine tuning of the low and high speed compression circuits can help…a company like PUSH can assist with this for a fee), but some people really like a progressive spring rate, so it’s a matter of personal taste.

    My vote: Install a spacer, drop the fork to 80mm. Drop the air pressure slightly to account for preload, possibly play with oil weights if you want to alter the behavior of the fork. If you are unhappy with the feel, you can probably tune it out with PUSH. But, hey, you might like the way it feels just fine.

    Good luck!

  • #103612

    Yes, your a2c will change by whatever you reduce the travel by. The spring rate will also be affected so you will have to add a few more psi to achieve the correct sag (according to the Fox link below). Keep in mind that reducing the travel will also change the geometry of your bike.

    Take a look at the link below. Go to Forks, 32mm, 32 Float 29, and take a peek at the suggested air spring settings for the various travel heights.

    http://www.foxracingshox.com/fox_tech_c … index.html

  • #103613

    You can achieve the proper sag two ways. Increase the negative air pressure and leave the positive air pressure static, or decrease the positive air pressure slightly and leave the negative pressure static.

    I prefer the second method. But, I recommend trial and error.

    EDIT:
    I’m not as familiar with Fox forks, but it looks like they don’t have independently adjustable air chambers, like Rock Shox. Therefore disregard my information on adjusting preload pressures and follow the Fox guidelines for increasing air pressure on a reduced travel fork.

  • #103614
    "comacruz" wrote

    Keep in mind that reducing the travel will also change the geometry of your bike.

    Changing the geometry is in fact the goal here. 😃

  • #103615

    Thanks for the replies. I’m a terrible wrench so I think I will call in the troops for the fork reduction operation. Just wanted to confirm that it will in fact change the A to C and thus, the geometry. Thanks.

  • #103616
    "maddslacker" wrote

    [quote="comacruz":28504qu7]Keep in mind that reducing the travel will also change the geometry of your bike.

    Changing the geometry is in fact the goal here. 😃[/quote:28504qu7]

    Sounded like he just wanted his bar at a lower height and didn’t want to change the HA, BB height, etc…

    OP – hope it all works out for you.

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