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Suspension advice on mismatched travel?

RelaxitscoolRelaxitscool Posts: 103
edited June 2009 in MTB workshop & tech
Hi all, I've purchased a BeOne Nirvana frame from CRC and built it up using my old hardtail. This includes my RS Revelation Dual Air with 140mm of travel. The rear shock on the frame is 100mm travel.

I've compensated for the extra height at the handlebars by removing a spacer, but will the extra travel of the fork completely mess up the geometry, and if so what can I expect?

Is there anything I can do to get around this until I have the money for some forks whose travel is batter matched?

Regards

Rob

Posts

  • bomberesquebomberesque Posts: 1,701
    shame you don't have the u-turn rev. I'm not sure if the "All Travel" 140mm revelation fork can be adjusted down using internal spacers? Maybe check your LBS as it'd need to be done professionally I suppose, if it's possible (I'm sure someone will be along in a minute to clarify that)

    As for the effect of running it as it is; most likely you will end up with a very slack head angle, however CRC says it has a 71 deg HA with a 100mm fork, so that will leave you with (I think) about 68 deg HA. Slack but not hideous. My Evil Sovereign is a HT but is similar geometrically and I have a RS pike 95-140mm uturn on it. I find 140 mm rideable but really too slack for normal stuff, especially climbing and slow speed maneuvouring are affected.

    You can run the fork with more than average sag (lower pressure in the chambers) but it'll likely feel odd and bottom out on you.

    finally, and I'm fairly sure it'll be OK, but you should check with CRC about using a longer than specc'd fork, as this does increase the lever arm on the headtube. Looking at the pics teh Nirvana has a gussetted tube and anyway looks like a pretty quality piece of bike but it is worth checking with them I think.
    Everything in moderation ... except beer
    Beer in moderation ... is a waste of beer

    If riding an XC race bike is like touching the trail,
    then riding a rigid singlespeed is like licking it
    ... or being punched by it, depending on the day
  • RelaxitscoolRelaxitscool Posts: 103
    Many thanks for the reply. I'll see if there are internal spacers, otherwise I guess its a new fork at some point.

    So the less head angle (slack) the less maneuverable it is at slow speed and climbing, why is that?

    Regards

    Rob
  • NorthwindNorthwind Posts: 15,475
    The other question is always whether the frame can take it, your forks are a lever so the longer they are, the stronger the frame has to be. I like the idea of mismatched travel myself, like the Orange Whateveritis, seems to me that there's no reason at all that both ends have to have the same travel, after all my hardtail has 130mm more travel front than rear :lol:

    But, this is a pretty big difference from standard and I'd be very cautious of it tbh. Even if it handles fine, which it might do, no guarantee it won't damage it.
    Uncompromising extremist
  • Steve_b77Steve_b77 Posts: 1,906
    I'm pretty certain you can drop the dual airs down to 120mm or 100mm with the aid of internal spacers.

    Damm site cheaper than a new fork.

    Is it a new Rev Dual Air or an older one?
  • RelaxitscoolRelaxitscool Posts: 103
    Well I just measured the stanchions, the visible bits when I'm not sat on the bike are 120mm, with 20mm of sag that brings it down to 100mm. I suppose that makes things a bit better.

    I think the forks are either 2007 or 2008. I bought them in th sale from JE James, def not this years model.

    By the way, thanks for the replies so far.

    Regards

    Rob
  • nicklousenicklouse Posts: 81,520 Lives Here
    prepare for a bike that feels like a tank and does not climb well.

    either get the fork sorted or changed.

    what is the frame designed for? a 100mm fork? so 80mm with sag. you are still a degree too slack and every time you hit a bump you will have a very stressed fork, headset and bushes.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • RelaxitscoolRelaxitscool Posts: 103
    Just back from my first ride on the bike. First impression, full suspension, how did I live without it, its juts so so smooth! I was expecting it to be hard work on the road section with pedal bob, but none, not a bit. I'm well chuffed.

    As you've probably gathered I'm not expert, but the bike seems to handle ok, its stable turns ok, feels ok, but then I don't really push it as much as some.

    Just to be safe though I'm going to contact Be One for advice with a view to altering the internal spacers and lowering the travel.

    Thanks for the replies.

    Regards

    Rob
  • Steve_b77Steve_b77 Posts: 1,906
    If it's an '07 or '08 Dual Air Rev it'll be 130mm travel, I'd say it'll be too much for the frame RE: warrantied fork travel.
  • RelaxitscoolRelaxitscool Posts: 103
    Thats interesting, so its not necessarily the travel but the overall length of the fork. So, do frame builders take this into account and recommend a fork for the frame or build in a degree of tolerance to allow for the different fork lengths?

    Regards

    Rob
  • RelaxitscoolRelaxitscool Posts: 103
    As a make shift solution I've reduced the pressure in the positive chamber to allow more sag. The forks are now around 90 to 95 mm when I'm on the bike, around 10-15mm to long but nothing to bad to funds permit.

    To try and reduce bottom out I'll increase compression.

    Thanks for all the replies so far.

    Regards

    Rob
  • bomberesquebomberesque Posts: 1,701
    Thats interesting, so its not necessarily the travel but the overall length of the fork. So, do frame builders take this into account and recommend a fork for the frame or build in a degree of tolerance to allow for the different fork lengths?

    Regards

    Rob

    most forks have a similar A2C (Axle to crown) length for the same amount of travel when unloaded
    Frame manufacturers generally recommend a fork travel based upon these common lengths accounting for "normal" sag with rider aboard, which I'm going to say is 25-35% depending on use although I'm sure someone here has a more accurate range....
    naturally the A2C changes as you ride the bike, which is what can make longer travel bikes tough to ride in technical stuff where you can be loading up the front end a lot
    I'd still write and ask their advice about a longer fork, but 30mm extra; I'm guessing they're not going to call the cops on you (although they might give you some "well, that's not covered under warranty" guff)

    if it feels OK to you and the BeOne CRC dudes don't cry about it, then enjoy! 8)
    Everything in moderation ... except beer
    Beer in moderation ... is a waste of beer

    If riding an XC race bike is like touching the trail,
    then riding a rigid singlespeed is like licking it
    ... or being punched by it, depending on the day
  • Matt 24kMatt 24k Posts: 186
    I have two mates with Beone Nirvana's bought new from CRC. One, a medium size, came with RS Tora 318's with 120mm of travel. The other, a large, was supplied with the same forks but set at 100mm of travel. After speaking to CRC they said it was not a problem to change the travel to 120mm which he did. Maybe 140mm is pushing it a bit but check with CRC before you try and adjust the travel of your forks.
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