Need advice on getting 27.5+ bike to handle like an old 26er- Mtbr.com
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  1. #1
    Ambivalent Luddite
    Reputation: Retro Dude's Avatar
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    Need advice on getting 27.5+ bike to handle like an old 26er

    I have a question on heat tube angle / fork rake and handling.

    Working on a design to get the same handing traits as an old Wicked Fat Chance (71deg HT / 1.75" rake) on a rigid 27.5+ bike.

    I ran some numbers(Bicycle Trail Calculator | yojimg.net), and to get the same trail/flop/mech trail numbers I can keep the 71deg head angle and increase the rake to 2.25"

    Would this give me the handling I'm looking for? Or are there other factors I'm not taking into account?

    Thanks
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  2. #2
    mtbr member
    Reputation: Eric Malcolm's Avatar
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    I am not going to give you any advise as I have not done this yet, guess I will in the future though.

    I will share this thought with you though. I built a bike that I use for multiple purposes. It has disc brakes that allowed me to use the same hubs and rimmed up a set of 26", 700c in both CX 35 and Road 23mm. My fixed HT angle is 70.5 degrees. The tyre width and resultant variations of wheel diameter give different trail figures and I have used rigid forks of 39 and 45mm off-set. The wheels don't make any real difference to the finished feel to be honest. It always rides/responds in familiar fashion whichever option I fit. I found that the fork offset made a greater difference to the final result and since you are going to make a fork?, then I suggest you make 2 or 3 at various off-sets and find the ideal for youself.

    Regards and good luck

    Eric
    If I don't make an attempt, how will I know if it will work?

  3. #3
    mtbr member
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    I can't speak to the calculations. I have built two 29er bikes using carbon frames imported from China. I have been riding an old Cannondale CAD3 on which the RockShock finally gave out so it became an excuse to spend money to play around with the 29er carbon frames.

    What I have found it that one carbon frame that has a longer rake (wider head angle) is similar to the impact of riding a raked-out motorcycle: since more of the weight is distributed further back of the axes of the front wheel, you get a lighter feel.
    I have just put these bikes together but have enough time on them to have some opinion: I do not recommend a longer rake if you are wanting the bike to ride similar to a 26er. The shorter axes of the 26er mean that when you are riding on trails/all-mountain or downhill you have your weight distributed so that you have tighter control. You also have a firmer feel to the front shock because it is not angled... the physics of the compression on the forks is more direct. You can probably find discussions of motorcycle raking of the head/forks that is similar.

    One impact of the shift to 27.5 and 29er wheelset frames is that it provides a more tolerant and 'Cadillac' like ride. However, that also can result in less agility. I think that makes a carbon frame useful because it keeps the weight down while providing good rigidity. However, I think there is a tendency of the 29er frame to rake the front fork. The carbon frame that I have set up as an all-mountain rider has a slightly lower angle of rake making it ride a bit more like my old 26er. Because the weight is lower and the component selection of the drive train is 1x10 or 11, the overall experience is delightful.

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