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  1. #1
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    Axle --> Crown Reba

    Can somebody help me with the axle crown lenght of an Reba, at 85 MM & 100 MM.
    I'm thinking of replacing my SID with an REBA , just wondering if it will affect my geometry.

    Thanks

  2. #2
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    Quote Originally Posted by Dex11
    Can somebody help me with the axle crown lenght of an Reba, at 85 MM & 100 MM.
    I'm thinking of replacing my SID with an REBA , just wondering if it will affect my geometry.

    Thanks
    458/473 +/- 5mm
    http://www.bullteksports.com/catalog...Suspension.htm

  3. #3

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    Will setting the Reba to 115 raise the front of the bike 15mm from the 100 mm setting? Will 15 mm affect geometry?

  4. #4
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    I don't mean to Hijack your thread...

    ..but I'm trying to determine the same thing regarding replacing my Marz Dirt Jam Comp with the Reba SL. The axle crown length of the Marz and Reba are 488mm at 100mm & 115mm of travel respectively. I have an email in to Kona with the same quesion but I was curious if someone here would have an answer. I guess my Q's are:

    Will the Reba work for me at 115mm?

    Or should does it need to be run at 100mm?

    Or will it not work at all?

    Thanks for any responses. My apologies to Dex for imposing on this thread, but if someone here has answers it might be helpful to someone in the future doing a search to find multiple questions/answers in the same thread .

    Patrick


    Quote Originally Posted by Dex11
    Can somebody help me with the axle crown lenght of an Reba, at 85 MM & 100 MM.
    I'm thinking of replacing my SID with an REBA , just wondering if it will affect my geometry.

    Thanks

  5. #5
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    Same thing here, my thinking is i can gain 10mm of travel with the Reba at 115mm over the Marz at 105mm both A/C measure 488.


    The fork will drop 15mm if you turn the travel down but the bars will not be 15mm lower as some of the length get lost in the rake and so on.

    I measured this on my mates and 15mm dropped on the uturn was only 7mm in bar height even tho the fork was 15mm shorter. Weird or what...

  6. #6
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    @ westin : thanks, very helpfull site.

    @ PcinSC : No problem, I see more people with the same questions. Maybe I should
    should change the topic to : How does axle-crown lenght affect your
    geometry ?

  7. #7
    MK_
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    For roughly every 20mm of A-to-C height of the fork your head angle changes one degree. Bottom bracket is affected roughly a quarter the AC change. If one fork at 100mm of travel has X AC height, and another fork has X height at 115mm, then your handling will not be affected at all, your front will simply sink deeper on big hits. Keep in mind that sag is in %, so X% of 115mm is more than X% of 100mm, so you'll have a slightly steeper head angle and slightly lower bottom bracket.

    _MK

    "The things you get fired for when you’re young are the same things you get Lifetime Achievements for when you’re old."

  8. #8
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    Quote Originally Posted by Dex11

    @ PcinSC : No problem, I see more people with the same questions. Maybe I should
    should change the topic to : How does axle-crown lenght affect your
    geometry ?
    I got an email back from tech @ kona. Here is what they wrote, verbatim:

    Go with it at 100mm. The more travel you have on a hardtail the more
    unbalanced it feels as you compress the suspension. Starts out slack when
    topped, out and then speeds up real fast when you hit a bump or the brakes.


    Soooo...it appears they feel I should run the Reba at 100mm even though the axle-crown length is a bit shorter (15mm) than what I'm currently using. It doesn't quite add up to me, though. Because if I run it at 100mm travel I'm going to make the head tube steeper by almost a degree, according to MK's numbers (and I'm taking MK's word for it that that "conversion" is correct). This will make it more squirrelly than it is now, and even more squirrelly on hits or while braking, right?

    Now, I like how the Hoss handles currently, but sometimes, when the fork gets compressed turning a turn, admittedly because my cornering technique may be bad (too much weight forward), I can feel the steering "sharpen up" and it throws me off balance a bit. Admittedly this happens not that frequently, usually on tighter (downhill) switchbacks, especially at slower speeds. This coincides with what Kona Tech said. But is seems like the shorter 100mm travel setting position of the Reba (and resultant shorter A-C height) will make this worse, not better. I just don't want to exacerbate this "condition" by running a too short A-C length.

    I want to have the Hoss set up for general trail riding (lots of rocks, ups and downs not too steep). I'm willing to lay off the light freeride stuff I do to have a fork and bike that performs well on the trail.

    Here are the numbers (I'll use MK's rough ratio of 20mm:1 degree) as worked out by me, the ignorant newbie, with my interpretation of what will happen to the handling:

    Currently with Marzocchi Dirt Jam Comp (assume sag at 20%, ~20mm)
    100mm travel
    80mm sag height
    (I don't even know if this is a term, but you know what I mean: 100mm - 20mm = 80mm )
    488mm A-C height (468mm with sag)
    69.5 deg head tube angle
    Result: bike handles ok. Fork performance sub-par.

    Projected with Reba at 100mm (assuming same sag as Marz at 100mm)
    80mm sag height
    473mm A-C height (453mm with sag)
    ~70.25 deg head tube angle
    Seat tube angle (steeper) and BB height (lower) will be altered by fractions of a unit.
    Expected result: Undesirable sharper turning.

    Projected with Reba at 115mm (with same % of sag, which would be ~23mm)
    92mm sag height
    488mm A-C height (465 mm with sag - note it's only 3mm lower then the Marzocchi)
    ~69.35 degree head tube angle
    Seat tube angle (shallower) and BB height (higher) will be altered by fractions of a unit.
    Expected result: Similar handling to current set-up; slightly extended travel; plusher, better performing fork.

    It sure seems to me that I should run it at 115mm to get the best performance. Maybe my numbers are wrong, or my interpretation is wrong, or I'm missing a dozen other variables that need to be considered. If so, feel free to let me know. Maybe I should just shut-up, put the fork on and ride the bike. OK, I will. But first, I'll take all opinions.

    Patrick

  9. #9
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    Patrick,
    I would agree with you that the reba at 115mm will be the same as a marz at 100mm.
    As you say the percentage of sag 20percent of 15mm = 3mm is nothing,so the overall feel will be the same.
    The A/C is the important thing and if it is the same it has to feel the same in terms of geometry.
    Reading the answer from Kona they seem to have neglected the fact that the A/C measurements are the same.
    There answer is correct if you were uping the A/C measurement by 15mm but your not.
    If you have the ETA on you Marz lock it down 15mm and that is how the Reba at 100mm will feel.

  10. #10
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    Quote Originally Posted by CragRat
    Reading the answer from Kona they seem to have neglected the fact that the A/C measurements are the same.
    There answer is correct if you were uping the A/C measurement by 15mm but your not.
    If you have the ETA on you Marz lock it down 15mm and that is how the Reba at 100mm will feel.

    Thanks, at least one person doesn't think I'm crazy. Regarding Kona's response, I emailed the tech the specs for the Reba. So he should've been working with the same numbers as me. But he came to a different conclusion. I should email him back and show this thread, see what he thinks.

    And unfortunately I don't have ETA on my current fork. It's a set-it and forget-it OE dirt jump fork. Beefy, but not a whole lot of finesse. Thanks for the response.

    Patrick

  11. #11
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    Quote Originally Posted by PCinSC
    Thanks, at least one person doesn't think I'm crazy. Regarding Kona's response, I emailed the tech the specs for the Reba. So he should've been working with the same numbers as me. But he came to a different conclusion. I should email him back and show this thread, see what he thinks.

    And unfortunately I don't have ETA on my current fork. It's a set-it and forget-it OE dirt jump fork. Beefy, but not a whole lot of finesse. Thanks for the response.

    Patrick
    The nice thing about the REBA is that changing the travel is quite easy and up to you. They mostly come @ 100mm travel so get it and try it at that setting - you might be amazed what a little dialed-in Motion Control on the REBA can do for your handling/diving. If you don't like it at 100mm - to quick - then take out all spacers to set it to 115mm travel. Best thing is no matter what, the REBA is a great fork with the option of 3 travel settings, You WON'T b disapointed if you purchase it!! MUCH stiffer than the SID.
    Quote Originally Posted by Harold
    You're doing mtbr wrong, you're supposed to get increasingly offended by the implications that you're doing ANYTHING wrong.

  12. #12
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    Quote Originally Posted by LyNx
    The nice thing about the REBA is that changing the travel is quite easy and up to you. They mostly come @ 100mm travel so get it and try it at that setting - you might be amazed what a little dialed-in Motion Control on the REBA can do for your handling/diving. If you don't like it at 100mm - to quick - then take out all spacers to set it to 115mm travel. Best thing is no matter what, the REBA is a great fork with the option of 3 travel settings, You WON'T b disapointed if you purchase it!! MUCH stiffer than the SID.
    Do you know if it's a pain in the neck to take out the spacers? I'm pretty sure it's going to come set at 100mm so it would be easy just to leave it there and try it out. What are your thoughts on the geometry issues? How did you like the fork when you had it?

  13. #13
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    Quote Originally Posted by PCinSC
    Do you know if it's a pain in the neck to take out the spacers? I'm pretty sure it's going to come set at 100mm so it would be easy just to leave it there and try it out. What are your thoughts on the geometry issues? How did you like the fork when you had it?
    Actually I was very fearful of performing the service myself, but since I live on a very small island with no such services I had to do it. I've had my Trance3 since Valentines Day and it came with a bum DUKE XC (bushings were knocking after only 2 weeks) so I sent it back up to the US for warranty and purchased the REBA to ride in the mean time - Also it was a planned upgrade for the Trance, but wasn't sposed to happen till about 6 months down the line. In the 8.5 months I've had the REBA I put over 2200 miles on it without any attention so it was most definitely in need of a service so I finally sucked it up and gave it a whirl - it was a bit daunting at first, but in reality was very simple.

    Best advice is heed all the "tools you will need" advice and make sure you at least have an accurate syringe (don't guess about oil levels, they are very critical to the forks performance), about 3 times more 5wt oil than 15wt ( the REBA uses both) get about an 8oz bottle of 5wt. Follow the isntructions in the PDF and you should be fine, also consider maybe getting a set of the Endyrofork seals to replace the factory ones - Chris is very helpful if you do decide and knowledgeable.

    I'm still running the REBA and it's now good as new after the service and buttery smooth. The change to me wasn't all that drastic - actuallly kinda hardly noticeable, but you do notice it Biggest thing it ads is more plushness (you can drop the pressure a bit and get a smoother, more progressive stroke). For a sub $400 fork there is none equal to the REBA.
    Last edited by LyNx; 11-19-2005 at 12:26 PM.
    Quote Originally Posted by Harold
    You're doing mtbr wrong, you're supposed to get increasingly offended by the implications that you're doing ANYTHING wrong.

  14. #14
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    70 or 71 degree head angle with 100mm Reba

    I need help...any comments are welcome-i'm looking for a MTB but i have no idea which to get. A friend told me to get a bike with 70 degree head angle for better cornering and
    stabilty going downhill. 70 degree head angle with 100 front fork will suffer from climbing,
    twitchy and wandering-correct?
    How about 71 degree head angle with 100mm Reba fork...give me the pros and cons?
    Thanks

  15. #15
    MK_
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    Quote Originally Posted by akazan
    I need help...any comments are welcome-i'm looking for a MTB but i have no idea which to get. A friend told me to get a bike with 70 degree head angle for better cornering and
    stabilty going downhill. 70 degree head angle with 100 front fork will suffer from climbing,
    twitchy and wandering-correct?
    How about 71 degree head angle with 100mm Reba fork...give me the pros and cons?
    Thanks
    The steeper the head angle the twitcher the ride quality. Climbing is a little easier. Slacker head angle gives you a more stable ride.

    _MK

    "The things you get fired for when you’re young are the same things you get Lifetime Achievements for when you’re old."

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