Retrofit 650b wheels onto a 29er?...- Mtbr.com
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  1. #1
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    Retrofit 650b wheels onto a 29er?...

    My first post on this forum. I came off a 26 inch hardtail and built up a Motobecane 29er Ti Fly from the frameset. The bike is great but have to say I am not enamored with the spool up of the heavier wheels. Without question the bike rides a lot better than my 26er but after owning it for a while now there is no mistake the 29er takes more energy to get up to speed. The bike does ride like a Cadillac though for a hardtail. I honestly do miss my 26er that I sold off to build the 29er...but not the harsher ride which is a key element of why I built the 29er. I am old....as in a fit 50 something guy who still likes to ride fast albeit not too rough XC fire roads.

    The BB height on my new 29er is pretty high and was thinking...instead of a complete reversion back to a 26er to get that spry acceleration back, why not split the difference and maybe mount some 650b wheels on my 29er? Do you guys think this would be worthwhile? To me hardtail to hardtail it comes down to ride compliancy relative to acceleration. Maybe I can't have my cake and eat it too.
    Your advice would be appreciated.

  2. #2
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    The BB and pedal clearance drops 3/4 inch with the lower axles of 650b (27.5") wheels on a 29'er frame and fork. For fireroad riding that lower pedal clearance could be OK, but possibly a problem pedaling out of corners.

    Have your tried lower gearing on the 29'er such as 20/30/40 rings, or the new 12-36 Shimano HG cassette? The HG cassette is heavy, I'm using it on my 650b bike and while riding I really cannot feel the added 1/4 pound over the XT 11/34 I was using before, and the spin up, acceleration, and climbing seems easier everywhere.

  3. #3
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    Actually Derby I think changing gearing is no substitute for the increased wheel mass of the 29er. I virtually never use my granny gear. Gearing is fine. I am in the middle of my cassette in the middle front ring when ripping fireroads at 15mph. I know no bike is all things. I just miss the quick acceleration of my 26er. Maybe I remember the easier acceleration of that bike more than painful memories of how it punished my body compared to the 29er. To me the acceleration difference is as striking as the ride compliancy difference....both hardtails but very different bikes. I believe the difference in 26-29 wheel diameter accounts for 2 cogs in back in gear inches. Its the inertia of the wheels that I feel....I know they keep that momentum better as well...but I miss the quick burst of the 26er.
    Thanks.

  4. #4
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    Why not run a 650b in the rear.

  5. #5
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    I'm not sure what wheels you have on your 29er - but they could be the culprit - not necessarily the wheel size mind you - but the quality level/weight of the 29er wheelset that you are currently running.

    What is your 29er wheelset? Is it high end or more of a budget set?

  6. #6
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    Quote Originally Posted by MMcG
    I'm not sure what wheels you have on your 29er - but they could be the culprit - not necessarily the wheel size mind you - but the quality level/weight of the 29er wheelset that you are currently running.

    What is your 29er wheelset? Is it high end or more of a budget set?
    No question my wheelset contributes to the problem...Mavic TN719's with Shimano XT hubs + tubes...running Nanoraptor 2.1's. Wheels aren't boat anchor heavy tho. Was thinking maybe 650b and build lighter. I am interested in how many think a 29er HT frame is conducive to a 650b transplant.

  7. #7
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    Quote Originally Posted by djembe975
    Why not run a 650b in the rear.
    Two reasons:
    - May not be enough difference.
    - Changes trail and slows steering response.

    Why not run 650b both front and rear?

  8. #8
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    If you've got the $$ - give it a go!

  9. #9
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    Quote Originally Posted by MMcG
    If you've got the $$ - give it a go!
    Give what a go? If nobody here has ever replaced their 29er wheels with 650b wheels and can report any feedback, I prefer not to be the pioneer.
    Last edited by dirtrider7; 06-09-2010 at 02:14 PM.

  10. #10
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    I've gone back and forth on one of my hardtail frames.

    the 650bs make the bike a bit more nimble and lighter overall and a bit quicker to accelerate, but at the same time the big 29er front wheel does roll over trail obstacles better.


    The bb height of the frame in 29er mode is 12.75" high (somewhat high for 29er standards - but good to avoid pedal strikes etc. here in CT)

    It dropped down to just a tad higher than 12" when I went dual 650b and I did get the occasional pedal strike - but nothing of concern.




    The set up with both wheelsizes was in single speed mode btw. 32:22 withe my 29er SS wheelset and 32:21T with my 650b hoops.

    Hope this helps you out a bit.

  11. #11
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    Quote Originally Posted by MMcG
    I've gone back and forth on one of my hardtail frames.

    the 650bs make the bike a bit more nimble and lighter overall and a bit quicker to accelerate, but at the same time the big 29er front wheel does roll over trail obstacles better.


    The bb height of the frame in 29er mode is 12.75" high (somewhat high for 29er standards - but good to avoid pedal strikes etc. here in CT)

    It dropped down to just a tad higher than 12" when I went dual 650b and I did get the occasional pedal strike - but nothing of concern.




    The set up with both wheelsizes was in single speed mode btw. 32:22 withe my 29er SS wheelset and 32:21T with my 650b hoops.

    Hope this helps you out a bit.
    Thanks MMcG. Sounds like you've tried it but were underwhelmed by the difference.
    Perhaps that explains the more binary approach to the sport...either go 26 for nth degree lightness and quickness or 29'er with improved rollover and momentum as you report... the increment of 650b in between is perhaps kind of caught in the middle of benefit versus downside...not to mention less wheel and tire availability. I thought perhaps 650b maybe the best of each but perhaps not.
    Cheers.

  12. #12
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    I think it is a bad idea just in the sense that your pedals will hit everything. You would be better off building a lighter 29er wheelset, Shimano hubs weigh a ton.
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  13. #13
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    Quote Originally Posted by ljsmith
    I think it is a bad idea just in the sense that your pedals will hit everything. You would be better off building a lighter 29er wheelset, Shimano hubs weigh a ton.
    Hubs are analogous to static weight because they are at the center of rotation. Lighter hubs don't make much difference in bike acceleration and why you have to look carefully at wheel component specs.
    You probably are right about the difference of lighter wheels ergo spokes, rims and tires sans tubes though. The light make right argument filters all the way down to 26ers. A light 26er is going to be lighter than a light 650 or 29er apples to apples. So no 29er or 650 bike will ever accelerate with a 26er.
    Only hope is the benefit of the larger wheels offsets some of the inertia of the larger wheels at start up which many believe they do. For me a 29er makes sense for training because of ride quality and injury prevention. For racing I feel faster on a 26er.

  14. #14
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    Quote Originally Posted by dirtrider7
    ... For me a 29er makes sense for training because of ride quality and injury prevention. For racing I feel faster on a 26er.
    FWIW...I have two of the almost the exact same SS race bikes (literally the same frame, geometry, bars, components, etc.). One is a 69er, the other is a B9er. Overall I am faster on the B9er. The 26 rear is great for the short steep climbs, but at the end of the day my race times are faster with the 650B rear wheel. I also have a 29er SS and I ride like poetry in motion on that big rear wheel.

  15. #15
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    I know nothing about hardtails but when I considered 650's into a 29" FS frame there were a few apparant issues : BB height too low, the rear chainstay is too long - can't correct that, the steering may quicken due to a new trail figure. 650 makes more sense for a 26" trail bike.

  16. #16
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    Looking from a rolling mass perspective, and considered with same hubs, spoke count and type (eg. 2.0/1.8 DB), rim width, tires, tubes, knob height, and spoke length difference... 650b wheels will drop rolling mass by about 5.5% from 29 inch wheels. 26 inch wheels would drop rolling mass by 9.4%. (see background notes below).

    So if you had a pretty light 29'er wheel set that weighed 2000 grams adding 1000 grams for light racer tires, 650b wheels with the same build would drop about 165 grams, over 1/3 lb. of rolling mass (3000g * .055).

    26 inch, would drop about 282 grams, well over 1/2 lb. of rolling mass compared to 29'er wheels (3000g * .094).

    You can see by the math that 650b drops almost 2/3's of the rolling mass difference to 26 inch below the rolling mass of a 29'er wheels and tires.


    Background notes:

    - 26x2.0 tires are commonly very near 26.5 inch Outer Diameter equaling near 83.252 inch circumference
    - 650b/27.5 in. OD is about 86.394 circ. and 3.8% greater than 26
    - 29 in. OD is about 91.106 circ. and 5.5% greater than 650b, and 9.4% greater than 26

  17. #17
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    Thanks guys. Perhaps at the end of the day retrofitting 650b wheels onto a 26 inch mtb does make the most sense versus mounting b wheels on a 29er frameset.
    I was curious if the latter had been done with any frequency and what the benefit if any had resulted.
    I know the biggest impediment with 650b wheels which perhaps cuts into their popularity...chicken and egg argument....is tire and wheel availability....not unlike the slow start that 29 wheels became available in mtbing.
    Thanks again.

  18. #18
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    Not underwhelmed at all. I just have a limited budget and only one good set of 650b wheels right now. When I get the $$ I most likely will go all 650b for off road duty.

    And possibly even 650b for road - especially after all the great reports on the new Pari-Moto tires from Kirk.



    I would say for me at my height - dual 650b is the optimal wheel size for mountain bike riding.

    Quote Originally Posted by dirtrider7
    Thanks MMcG. Sounds like you've tried it but were underwhelmed by the difference.
    Perhaps that explains the more binary approach to the sport...either go 26 for nth degree lightness and quickness or 29'er with improved rollover and momentum as you report... the increment of 650b in between is perhaps kind of caught in the middle of benefit versus downside...not to mention less wheel and tire availability. I thought perhaps 650b maybe the best of each but perhaps not.
    Cheers.

  19. #19
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    There was an article comparing wheel/tire diameter and width to perceived performance in a recent issue of the Bicycle Quarterly. I don't remember the exact conclusions, but it was something to the effect that a 700CX30c and 650BX40c had comparable performance (ideal for the diameter of each)

    Keep in mind that these were road bikes. It might be interesting to do a similar test offroad. If someone has a set of Stans 355 in a 29er size, I could compare to my 650Bs

  20. #20
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    Quote Originally Posted by intheways
    There was an article comparing wheel/tire diameter and width to perceived performance in a recent issue of the Bicycle Quarterly. I don't remember the exact conclusions, but it was something to the effect that a 700CX30c and 650BX40c had comparable performance (ideal for the diameter of each)

    Keep in mind that these were road bikes. It might be interesting to do a similar test offroad. If someone has a set of Stans 355 in a 29er size, I could compare to my 650Bs
    Ideal in what context?...net footprint? On the road a 23/25mm tire would be faster so not ideal relative to speed. I believe the idealization here is wheel/tire weight equivalence.

  21. #21
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    Quote Originally Posted by dirtrider7
    Ideal in what context?...net footprint? On the road a 23/25mm tire would be faster so not ideal relative to speed. I believe the idealization here is wheel/tire weight equivalence.

    I believe they were using subjective evaluation of overall performance (Comfort, cornering, stability, and speed)

  22. #22
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    if you're buying 650b wheels anyway why not toss them on the 29er and see how you like it. it's really the only way you will know how the setup feels in your trail environment. if you don't like it then swap out the frame.

    in general, i wouldn't be crazy about making compromises that are not necessary, such as the elongated wheelbase and reduced fork travel of running 650b wheels on a 29er frame. i would rather run 650b in a 26er and "gain" in both areas. personal preference though, a "gain" for me might not be for someone else.
    Last edited by salimoneus; 06-11-2010 at 03:44 PM.

  23. #23
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    Quote Originally Posted by salimoneus
    if you're buying 650b wheels anyway why not toss them on the 29er and see how you like it. it's really the only way you will know how the setup feels in your trail environment. if you don't like it then swap out the frame.

    in general, i wouldn't be crazy about making compromises that are not necessary, such as the elongated wheelbase and reduced fork travel of running 650b wheels on a 29er frame. i would rather run 650b in a 26er and "gain" in both areas. personal preference though, a "gain" for me might not be for someone else.
    Good advice but gain isn't all encompassing. Some may not like the higher BB of 650b wheels on a 26er frame. I do agree with your overall comments tho. Thanks.

  24. #24
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    mtb action just did a comparison on the 26er,29er,and 650b and the 650b was the clear winner..I dont remember what brand bike they were testing but it had frames desinged for each wheelset. I have wondered the same thing yoou are wondering but never thought about the bb height. Im glad somebody pointed that out. I to wish I had the snappy accelleration especially up hills that come right after a corner but when it comes to going down hill its hard to beat the freight train feel of the 29er. the short climbs after a down hill section isnt a problem either.
    I have a set of american classsic 29ermtb's on my epic and felt an immediate difference when I put them on but still I can tell I dont have that snappy accell. I used to have on my old hard tell 26er.. i wish I could do a comparison back to back of the 26 epic and the 29 epic and see which I would prefer but thats not likely to happen so as for now I will just enjoy my 29er and suffer throught the pain and grind out the hills.

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