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  1. #1
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    Anybody ever mount 26" wheels on a 29er full suspension frame?

    Recently I'd snapped my frame and while I was waiting for word on a warranty replacement, I started shopping for a new or used full suspension frame in the 4-5" travel range to match my fork.

    While shopping, I found several nice looking frames for 29er's and just wondered how they would handle with smaller wheels on them. Would it be slacker or even steeper geometry?

    Turns out GIANT is giving me a new frame; but I would like slacker geometry than I currently have [71* HTA] so this question is still on my mind....Does anybody know?

  2. #2
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    No, running 26 inch wheels on a 29 frame is just dumb. I started to list reasons but...

  3. #3
    Trail Ninja
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    I don't think the angles change, unless you don't run similarly sized tires. The BB would be lower and the bike may likely twitchier. The bike may still feel stable at speed, accelerate a bit faster, but you lose out on all those 29er benefits that make it more capable like roll-over, extra traction, etc.

    Try a fatter tire up front, more travel up front, and a skinnier tire out back.

  4. #4
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    Re: Anybody ever mount 26" wheels on a 29er full suspension frame?

    You need to understand "trail". The steepness or fork offset of a 29er is all about compensating for the growth in trail you get with a larger wheel.

    A small wheel on a 29er geometry will put your trail in the realm of excessive twitchiness and instability. It is not a combination that will reward traditional mtb use. While you may compensate, conventional wisdom says you will be some distance from optimal behaviour. The pessimist will assure you it is downright dangerous.

    Sent from my GT-N7105 using Tapatalk 2

  5. #5
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    Quote Originally Posted by petercarm View Post
    You need to understand "trail". The steepness or fork offset of a 29er is all about compensating for the growth in trail you get with a larger wheel.

    A small wheel on a 29er geometry will put your trail in the realm of excessive twitchiness and instability. It is not a combination that will reward traditional mtb use. While you may compensate, conventional wisdom says you will be some distance from optimal behaviour. The pessimist will assure you it is downright dangerous.

    Sent from my GT-N7105 using Tapatalk 2
    Thank you...such is as I expected. I have no real training or understanding of rake/trail and how they affect things directly; but have tried to digest enough reading to guess that it was not a good idea.

    I kinda figured if anyone was going to try it, as large as this community is here, I might hear about it.

  6. #6
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    Crash course on trail

    Quote Originally Posted by SeaHag View Post
    I have no real training or understanding of rake/trail and how they affect things directly
    A little info on trail from wiki:

    Trail

    Bicycle head angle, rake, and trail
    A factor that influences how easy or difficult a bike will be to ride is trail, the distance that the front wheel ground contact point trails behind the steering axis ground contact point. The steering axis is the axis about which the entire steering mechanism (fork, handlebars, front wheel, etc.) pivots. In traditional bike designs, with a steering axis tilted back from the vertical, positive trail tends to steer the front wheel into the direction of a lean, independent of forward speed.[26] This can be simulated by pushing a stationary bike to one side. The front wheel will usually also steer to that side. In a lean, gravity provides this force. The dynamics of a moving bike are more complicated, however, and other factors can contribute to or detract from this effect.[1]
    Trail is a function of head angle, fork offset or rake, and wheel size. Their relationship can be described by this formula:[36]
    \text{Trail} = \frac{(R_w \cos(A_h) - O_f)}{\sin(A_h)}
    where R_w is wheel radius, A_h is the head angle measured clock-wise from the horizontal and O_f is the fork offset or rake. Trail can be increased by increasing the wheel size, decreasing or slackening the head angle, or decreasing the fork rake.
    The more trail a traditional bike has, the more stable it feels,[37] although too much trail can make a bike feel difficult to steer. Bikes with negative trail (where the contact patch is actually in front of where the steering axis intersects the ground), while still ridable, are reported to feel very unstable. Normally, road racing bicycles have more trail than touring bikes but less than mountain bikes. Mountain bikes are designed with slacker head angles than road bikes to improve stability for descents, and therefore have greater trail. Touring bikes are built with small trail to allow the rider to control a bike weighed down with baggage. As a consequence, an unloaded touring bike can feel unstable. In bicycles, fork rake, often a curve in the fork blades forward of the steering axis, is used to diminish trail.[38] Bikes with negative trail exist, such as the Python Lowracer, and are ridable, and an experimental bike with negative trail has been shown to be self-stable.[1]
    In motorcycles, rake refers to the head angle instead, and offset created by the triple tree is used to diminish trail.[39]
    A small survey by Whitt and Wilson[26] found:
    touring bicycles with head angles between 72 and 73 and trail between 43 mm and 60 mm
    racing bicycles with head angles between 73 and 74 and trail between 28 mm and 45 mm
    track bicycles with head angles of 75 and trail between 23.5 mm and 37 mm.
    However, these ranges are not hard and fast. For example, LeMond Racing Cycles offers [40] both with forks that have 45 mm of offset or rake and the same size wheels:
    a 2006 Tete de Course, designed for road racing, with a head angle that varies from 71 to 74, depending on frame size, and thus trail that varies from 51.5 mm to 69 mm.
    a 2007 Filmore, designed for the track, with a head angle that varies from 72 to 74, depending on frame size, and thus trail that varies from 51.5 mm to 61 mm.
    The amount of trail a particular bike has may vary with time for several reasons. On bikes with front suspension, especially telescopic forks, compressing the front suspension, due to heavy braking for example, can steepen the steering axis angle and reduce trail. Trail also varies with lean angle, and steering angle, usually decreasing from a maximum when the bike is straight upright and steered straight ahead.[41] Trail can decrease to zero with sufficiently large lean and steer angles, which can alter how stable a bike feels.[10] Finally, even the profile of the front tire can influence how trail varies as the bike is leaned and steered.
    A measurement similar to trail, called either mechanical trail, normal trail, or true trail,[42] is the perpendicular distance from the steering axis to the centroid of the front wheel contact patch.

  7. #7
    Trail Ninja
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    Stability at speed comes from wheelbase length. Steering stability comes from mechanical trail.

    Your wheelbase length is basically how far the axles are apart from each other, which shouldn't change from swapping 29er wheels to 26 wheels, without changing something else.

    More mechanical trail gives your steering more of a "self-righting" effect, which makes the wheel straighten itself to point forward at speed. More offset/rake reduces trail, reducing that self-righting effect, and allowing wheel to turn more directly. A slacker HA increases trail and makes that "self-righting" effect stronger, making steering feel lazier, but it also increases wheelbase, especially when combined with a longer fork. A steeper HA reduces trail. And as said before, the different wheel sizes affect trail.

  8. #8
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    Years ago when I still subscribed to MBAction they did a laughable comparison when 29ers started coming out. They took two gary fisher 29ers, and one of them they swapped on 26 inch wheels. Well, it doesn't take a genius to figure out that it didn't work too well. Not that I really care but are they still around?
    To appreciate the flowers you must also walk among s**t to know the difference

  9. #9
    T.W.O.
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    Yes I have on both full suspension and HT, both are Niners. It was awesome corners like it was on rail with the low bb. That said, it would never work on the trail as you'd hit every thing in it's path, and/or pedaling out of corners

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