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Adjustable Front Susp.

The Northern MonkeyThe Northern Monkey Posts: 19,174
edited July 2008 in MTB workshop & tech
Alrite :)

I have a question that might seem a bit...simple...but its something thats confusing me/that i'm unsure about.

On my GT Aggressor XCR i have rock shox recon 351 forks that can be adjusted between 85-130mm travel and also has lock out.

I basically want to know in what conditions would you use the different lengths of travel. I mean theres no point in me having the ability to change something, if i don't fully understand the benefits/reasons for changing it.

Also, while i'm on the subject of my front susp, i'm having a bit of trouble understanding what the sag of the suspension should be.
I'm a heavy fecker...bout 16.2st so i understand that the sag will probably be more that it says it should be in the manual, but it seems to be sagging around 15mm if i have the forks set to 130mm travel. Would you say that thats sounds correct and will probably be the best i will get it for my weight?

Cheers for any input and help,
Ben

Posts

  • dave_hilldave_hill Posts: 3,877
    Adjusting fork travel changes the geometry of the frame and thus the ride characteristics of the bike.

    Setting the travel short (in your case to 85mm) will make the head tube angle steeper. This sharpens the steering and puts more of your weight over the front of the bike. You would use this setting for riding or tarmac or fire roads, or when climbing.

    If you set the travel long, you slacken the head angle of the bike. This means that the bike will become more stable at high speed and throws your weight further back - ideal for descending. If you try climbing with the forks set long, you will find that at very low speed the front wheel wants to lift all the time and the bars will probably "flop" from side to side.

    As an example, I have RS Pikes with U-turn - if I'm climbing for any length of time (or riding on tarmac or smooth surfaces) I set them to their shortest travel. For descending I wind them right out to 140mm. For general use, I set them mid way to about 125mm.

    15mm of sag sound like a good starting point. It could perhaps be a bit more but how you set the sag up is more about personal preference and how you ride than a defintive measure. Again as an example, I have about 20mm of sag set on my Pikes, but on my Orange which has 160mm Fox 36 forks, I have a bit more, about 35mm because I want the ride to be plusher and the forks more sensitive to small bumps.
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  • Excellent reply, cheers for that dave, was exactly what i was looking for :)

    I've spent the last week playing around with my susp, trying different settings etc and think i've got it how i like it now...just need to raise some funds so i can get back to the North Face.

    Being a student sucks :(

    One more question though, on the bottom of the right fork, there is the rebound setting. Am i correct in saying that this adjusts the speed at which the fork will "bounce back"? When would you set the rebound to a slower setting? I think i have mine set around midway, leaning more towards a quicker rebound. Would a slow rebound benefit lighter riders?

    Cheers Again.
    Ben
  • AnonymousAnonymous Posts: 79,667
    for general trail riding i set my fork for about 25% sag, so on a 150mm fork, that equates to about 38mm, for you that would be about 32mm. if you run too little sag, the fork will be too stiff and you wont get full travel and if you are carrying it, you might as well be using it. also, too little sag= poor small bump compliance.

    travel adjust is a personal thing, i actually like to ride my bike in the longest setting on the flat, the bike feels pretty stable but the flip side is that it turns slightly slower .so if that becomes a problem, i drop the front travel down to make the bike steer quicker. for the most part, shorter travel on the front is better for climbing as the bike tends to wander less and wont be so likely to wheelie.

    rebound is another experimental thing, too slow and the fork will pack down on repeated hits as the fork extends too slowly, if you set it too fast, the bike feels like a pogo stick. a general rule is to set the rebound slow enough that when you compress the fork when stood to the side of the bike, the fork is extended by the time you snap the fork off the ground, but only just. if you lift the wheel and the fork hasnt extended, speed it up a tiny bit more, until it is just fast enough
  • hmm cheers for that sheepsteeth gives me something else to think about. gonna have another play around with it tomorrow and see what i can come up with :)
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