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  1. #1
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    27.5 front 26 rear

    Hiya

    Anyone running a 27.5" front wheel on a 26" bike?
    I'm in the early stages of considering doing this to a ReignX with the existing 36 fork.

    I'd appreciate any advice or thoughts.

  2. #2
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    I just converted my Ventana Ciclón to 27.5/26 (posted in the Ventana forum). It was already overforked with a Fox 36, so I stepped down to a 150mm Magura Thor to keep the head angle reasonable. Even with the reduced travel, I've been very impressed with the improved front end traction and rollover, and I'm not going back to 26" up front.

    27.5/26 is a great combo, IMO (maybe better than 27.5/27.5), but one thing to keep in mind is that the offset of the Fox 36 is just 37mm, so you may end up with more trail than you like.

  3. #3
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    Thanks albeant. Solid advice.

  4. #4
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    the 27.5 will make far more difference in rolling resistance in the rear, as most fo your weight is centered over the rear of the bike. But it can't hurt to put one on, provided your fork arch will fit one.
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  5. #5
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    Thanks for the advice guys. Albeant's post on his Ventana Ciclón build was helpful. I dug up some other posts going back a couple of years and the consensus seems to be that the 27.5/26 combo is a good move.
    Once I've worked out how the fork will handle the 27.5 wheel and my preferred tire, I'll get me a wheel built.
    Thanks for taking the time.

  6. #6
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    I'm really interested in trying this on my NomadC

  7. #7
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  8. #8
    How much further ???
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    Quote Originally Posted by albeant View Post
    I've been very impressed with the improved front end traction and rollover, and I'm not going back to 26" up front.
    Wow really? You can really feel a difference in rollover with an additional 0.75 inch increase in radius? I must not be that good or in tune with my bike because Im still not sure my 29er truly rolls over anything better or if I just want to think it does. Kudos to you if you can detect such subtle differences.
    “Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did." Mark Twain

  9. #9
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    Quote Originally Posted by Douger-1 View Post
    Wow really? You can really feel a difference in rollover with an additional 0.75 inch increase in radius? I must not be that good or in tune with my bike because Im still not sure my 29er truly rolls over anything better or if I just want to think it does. Kudos to you if you can detect such subtle differences.
    I think rollover improvement on my 29er is very noticeable. It doesn't surprise me that it would be noticeable on a 650B wheel as well.

  10. #10
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    I thought about a big wheel in the front for my Superlight, but there really isn't anything about the handling of the bike that I think needs improvement. Of course I could do the experiment for less than $200 just to see, since I know my fork has room.

  11. #11
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    Im gonna subscribe to this thread. I think its a great idea. I agree with chargin rinos point about roll-over; however, some guys that want to retain the handling characteristic of a 26" rear wheel may view this as an acceptable compromise.

    Personally, I think you could do it on just about any 26" bike, but ideally, you'd get a 650B specific fork that has the same total stack off the ground as your old setup (so reduce your fork's A2C by the increase in axle height).

    The one thing I can't wrap brain around, and this is probably super picky, is: is there any disadvantage from a handling perspective of having two different axle height's off the ground?

  12. #12
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    Ride the Biscuit - Please see previous thread which mentions some of the handling aspects. I don't know much about geometry - i just ride - but I expect the increase in rake will effect steering and the a slightly higher bottom bracket will negatively effect cornering.

  13. #13
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    With respect to rear/front rollover, there's something else to consider. Granted, the rear wheel bears more weight, but the front wheel is the one that is getting "pushed" up and over obstacles. Think of it this way: when you're rolling your trash can out to the street (or wheeled luggage through an airport, etc.), it's much easier to get it over an obstacle if you pull it behind you instead of pushing it ahead of you. (And with respect to weight bearing, the stronger 26" wheel stays right where it's needed.)

    BTW, Syntace/Liteville seems to be building most of their new bikes this way:

    27.5 front 26 rear-liteville601.jpg

  14. #14
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    great post, been thinking about doing this for a while on my new bike, evil uprising with 650b 150mm Pike sounds pretty funtastic. a buddy of mine who's one of the best riders i've met used to ride a 29'er stumpjumper with a 26 rear wheel and absolutely destroyed steep technical trails on that set up and sweared by it.
    nothing witty here...

  15. #15
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    It is possible, just look at the Trek 69er. 26 rear, 29 front
    Also a lot of the old Cannondales had 24s in back and 26s up front.
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  16. #16
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    Hmmm. Now I'm going to have to try a 650b rear on my 29rd

  17. #17
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    Quote Originally Posted by toycrawler View Post
    Hmmm. Now I'm going to have to try a 650b rear on my 29rd
    Going backward usually doesn't work too well because it will drop your bottom bracket too much.

    For example, to make a 29/27 its better to start with the 27 add a big wheel up front.

    That's especially true with 69ers, but with 79ers it might not matter as much.

  18. #18
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    Quote Originally Posted by smilinsteve View Post
    Going backward usually doesn't work too well because it will drop your bottom bracket too much.

    For example, to make a 29/27 its better to start with the 27 add a big wheel up front.

    That's especially true with 69ers, but with 79ers it might not matter as much.
    Good point. Might just size one up and see what the measurements look like.

  19. #19
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    Since we're drifting toward a 27.5/29 discussion, I've been thinking about converting my 27.5 Kona Explosif to a 120mm 29er fork. But the cost of entry is fairly steep (fork + wheel), so it'll be a tough pill to swallow if it doesn't kill it on the trail.

    Thoughts on this? (setup, etc.)

  20. #20
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    The misnomers are misleading

    Quote Originally Posted by Douger-1 View Post
    Wow really? You can really feel a difference in rollover with an additional 0.75 inch increase in radius? I must not be that good or in tune with my bike because Im still not sure my 29er truly rolls over anything better or if I just want to think it does. Kudos to you if you can detect such subtle differences.
    The misnomers are misleading. The difference in radii between a "26er" and the "27.5er" is roughly ~0.5_inch, not ~0.75_inch.

    The ISO/ERTO rim diameters:
    "26er"= 559_mm
    "27.5er"= 584_mm
    "29er"= 622_mm

    584_mm - 559_mm = 25_mm = 0.98_inch

    So if comparing the two wheel sizes using tires with similar cross section, the radius of the "27.5er" is approximately 0.5_inch larger than the radius of the "26er".


    edit: The effect of position of a point mass in the moment of inertia of a disc is proportional to the square of radial distance of that mass from the center of rotation. The effect of a change in mass is directly proportional to that change in mass. So the radial distance has much stronger effect in the sum. Thats why it is difficult to feel a difference in hub weights but easy to feel a significant difference in tire weights. A larger wheel diameter would be far more significant by moving that tire and rim mass outward from the center of rotation. And because the larger wheel diameter also has a larger circumference, mass is not just moved outward but is increased as well. What the rider feels is more closely correlated to his effort needed to change angular momentum. Angular momentum is the product of angular velocity and moment of inertia, so while the larger wheel increases mass and moves that mass further out on the disc, it also turns slower at comparable speed over the ground, and the reduced angular velocity mitigates a small portion of the increase in moment of inertia.

  21. #21
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    Here's my 67.5'er!

    This thing manuals like a dream! I offset the bigger wheel with a shorter seat stay, shorter rockers and lowering the fork. It was sitting at roughly 15" which is way too tall. I did not expect that, but I hadn't checked the spec on the Vengeance beforehand. It's freegin' tall! Anyway, I have a set of offsets coming and I'll prolly lower the fork another 5mm or so.

    The handling through regular terrain and obstacles is noticeable, which is mainly what I was looking for. This is the first air fork I've owned in some time, so I'm still getting used to it in more technical situations. Overall, the improved geometry has been a nice surprise as I wasn't expecting much.

    27.5 front 26 rear-lil-ripper-3-.jpg

  22. #22
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    Quote Originally Posted by JRT_in_WMass View Post
    The misnomers are misleading. The difference in radii between a "26er" and the "27.5er" is roughly ~0.5_inch, not ~0.75_inch.

    The ISO/ERTO rim diameters:
    "26er"= 559_mm
    "27.5er"= 584_mm
    "29er"= 622_mm

    584_mm - 559_mm = 25_mm = 0.98_inch

    So if comparing the two wheel sizes using tires with similar cross section, the radius of the "27.5er" is approximately 0.5_inch larger than the radius of the "26er".


    edit: The effect of position of a point mass in the moment of inertia of a disc is proportional to the square of radial distance of that mass from the center of rotation. The effect of a change in mass is directly proportional to that change in mass. So the radial distance has much stronger effect in the sum. Thats why it is difficult to feel a difference in hub weights but easy to feel a significant difference in tire weights. A larger wheel diameter would be far more significant by moving that tire and rim mass outward from the center of rotation. And because the larger wheel diameter also has a larger circumference, mass is not just moved outward but is increased as well. What the rider feels is more closely correlated to his effort needed to change angular momentum. Angular momentum is the product of angular velocity and moment of inertia, so while the larger wheel increases mass and moves that mass further out on the disc, it also turns slower at comparable speed over the ground, and the reduced angular velocity mitigates a small portion of the increase in moment of inertia.
    **** yeah!

  23. #23
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    Quote Originally Posted by JRT_in_WMass View Post
    edit: The effect of position of a point mass in the moment of inertia of a disc is proportional to the square of radial distance of that mass from the center of rotation. The effect of a change in mass is directly proportional to that change in mass. So the radial distance has much stronger effect in the sum. Thats why it is difficult to feel a difference in hub weights but easy to feel a significant difference in tire weights. A larger wheel diameter would be far more significant by moving that tire and rim mass outward from the center of rotation. And because the larger wheel diameter also has a larger circumference, mass is not just moved outward but is increased as well. What the rider feels is more closely correlated to his effort needed to change angular momentum. Angular momentum is the product of angular velocity and moment of inertia, so while the larger wheel increases mass and moves that mass further out on the disc, it also turns slower at comparable speed over the ground, and the reduced angular velocity mitigates a small portion of the increase in moment of inertia.
    with short stems and wider bars the angular velocity would be even less a negative factor on the larger 27.5 wheel with more upside on rollover characteristics than the 26, sounds like a reason to give it a shot.
    nothing witty here...

  24. #24
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    Quote Originally Posted by 2w4s View Post
    with short stems and wider bars the angular velocity would be even less a negative factor on the larger 27.5 wheel with more upside on rollover characteristics than the 26, sounds like a reason to give it a shot.
    Next I'm going to hear that short stems are going to solve the Middle East problem.

  25. #25
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    Quote Originally Posted by JRT_in_WMass View Post
    What the rider feels is more closely correlated to his effort needed to change angular momentum. Angular momentum is the product of angular velocity and moment of inertia, so while the larger wheel increases mass and moves that mass further out on the disc, it also turns slower at comparable speed over the ground, and the reduced angular velocity mitigates a small portion of the increase in moment of inertia.

    Actually, the reduced angular velocity completely mitigates the increase in moment of inertia. It takes no more effort to accelerate a large wheel of the same mass as a small wheel. I can prove that mathematically if you like.

    But, large wheels are usually somewhat heavier. But they also have a smaller approach angle to roll over obstacles, and also have a lower rolling resistance directly attributed to the larger diameter. Overall, there are pluses and minuses to any wheel size (I personally like them all for different reasons), but the bottom line is not going to be found in an equation, its going to be decided in public opinion, and you can't argue that a lot of people are riding big wheels and appreciating what they have to offer.

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