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  1. #1
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    650b up front/26" rear -- ROCKS AND ROLLS!

    After 3.5 years of riding my Mojo, had no idea the design could be perfected... Onto my 2010 32-Talas-150 FIT/RLC/QR15 went a Stan's ZTR 355 650b wheel (w/Nevegal 27.5" x 2.1" DTC with Stan's solution) and immediately knew I'd never go back to 26" on front. I'll definitely keep the 26" wheel on rear, as I love the slight increase in rake angle and rearward saddle position, not to mention faster acceleration/less mass. As far as mass increase on front - the 650b wheel weighs the same as my 26" ZTR 355 wheel - maybe the newer American Classic 15QR hub weighs less, not sure - and the Nevegal tire adds (an unnoticeable) 80 grams more, total.

    I love the way this set-up rolls over rocks & roots, up and downhill, here on the endless, technical singletrack of SW NH. As well, the increase in rake angle makes it easier to manual, and the bottom bracket is slightly higher. I'd like to calculate how much more rubber from my Nevegal is contacting the ground around turns -- that must be significant -- another fraction of a knob? - my physics is too far gone - maybe someone has done this?

    ===

    Ibis Mojo (small)
    GravityDropper Turbo 2"/4" adjustable seatpost
    Formula Oro brakes
    XTR drivetrain and shifters
    2010 32-Talas-150 FIT/RLC/QR15 fork
    2007 RP23 shock (Pushed w/high volume)
    Stan's ZTR 355 650b (front)/26" (rear)
    Kenda Nevegal 27.5 / 26 x 2.1 conventional, w/Stan's solution

    etc!

  2. #2
    More Torque
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    Glad it is working out for you.

    Do you have any concern that the tire will jam under the crown during a hard impact?

    -D

  3. #3
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    impossible.

  4. #4
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    Quote Originally Posted by rshalit
    impossible.
    Impossible for you to be concerned about it, or impossible for it to happen?

  5. #5
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    The diameter of a 650b tire is just under 4% greater than the same size 26" tire. The larger volume 650b allows lower tire pressure. I'm not sure of the math, but the tire patch is probably 4% bigger in every direction from the center of the patch plus whatever the lower tire pressure can gain. The ability to lean harder when braking and cornering on the 650b adds more to the traction gain. The subjective gain in traction feel is far greater than just 4%, it feel more like 20% gain, not to mention the easier rolling.

  6. #6
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    impossible to happen - there's plenty of clearance and the wheel is fixed to axle at any rate.

  7. #7
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    Quote Originally Posted by rshalit
    impossible.
    If you let the air out of a Fox Float or Talas 140 or 150mm travel fork then a 650b sized 2.3 or greater will rub the crown. In my 3 years of closely following and participating in 650b experimentation I've never seen a report of someone actually bottoming and rubbing the tire while riding of any fork that clears the arch including Fox forks. Riders complain that they cannot access the bottom inch of travel of a Fox Float or Talas 140 or 150mm travel fork. There are modifications that can be done by a pro turner, or ambitious home mechanic to gain more usable bottom travel for these forks.

  8. #8
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    I truly don't understand - your first two sentences contradict, and the first, wrt letting the air out of the fork, why on Earth would someone do that and then ride around ?? Am I missing something? - the fork leg tubes are rigid to the axle, not to crown and stanchions, so how could a tire that has enough clearance, like mine, at more than a centimeter from tire to legs' brace, ever possibly rub anything?? Rubbing should I imagine depend strictly on the knobs, and why would someone run tires that rub - it would be obvious as soon as the tire was mounted and the wheel was put into the dropouts. While I usually run 2.1, I am certain a Nevegal 2.3 isn't going to touch anything. Perhaps you mean lateral fluctuation in the rim while cornering? I suppose there are some really flimsy rims with loose hubs out there that with a really fat 2.3 could rub in a turn.
    As to your third sentence, I have no trouble getting full travel from my fork - an inch is 2.54 cm - why would a gain in axle height of 3/4 inch (the radius) cause such a dramatic decrease in travel ? I have read more than one report in MTBR forums of people with 26" wheels not getting full travel with their Floats; I also read that, before FIT, nobody could get "full travel" due I believe to a bumper stop. I certainly never could get that last cm with my 2007 32 Float 140 RLC on my 26.
    What type of "participating in 650b experimentation" did you take part in? Are there reports and data available?
    Last edited by rshalit; 05-05-2010 at 09:18 PM. Reason: correction

  9. #9
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    What you guys may be missing is the requirement for more fork offset to corrospond to the larger tire. For nowm the best way to get there ( IMHO) is to run a 29"/100 mm fork and enjoy the benefits of a 42 mm offset vs. 38 mm offset of a 26" fork. The corrosponding A/C height is the same as a 140 mm fork/26" wheel. Best of both worlds, while eliminating the tire crown clearance issue. The better tracking of the 27" wheel minimizes the 40 mm of travel that is lost, I feel.

  10. #10
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    Quote Originally Posted by derby
    I'm not sure of the math, but the tire patch is probably 4% bigger in every direction from the center of the patch plus whatever the lower tire pressure can gain.
    The area of the tire contact patch is a function of the PSI of the tire, not its size. The size of the tire will affect the shape of the patch, but not the area. Of coarse this is all in theory and assuming that you are running a slick. Things change once you start introducing knobs on the tire.

  11. #11
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    Quote Originally Posted by buggymancan
    What you guys may be missing is the requirement for more fork offset to corrospond to the larger tire. For nowm the best way to get there ( IMHO) is to run a 29"/100 mm fork and enjoy the benefits of a 42 mm offset vs. 38 mm offset of a 26" fork. The corrosponding A/C height is the same as a 140 mm fork/26" wheel. Best of both worlds, while eliminating the tire crown clearance issue. The better tracking of the 27" wheel minimizes the 40 mm of travel that is lost, I feel.
    by "A/C" you mean axle/crown? Are you saying there's more trail and therefore the 27.5 front/26 rear doesn't handle as well? I really don't notice this for some reason - it corners quite well - should the increase in trail put more rubber in contact with ground perhaps compensating for increase trail? Isn't it a bit more complex than simply:

    trail = [(wheel radius) x Cos(head angle)] - rake/sin(head angle)

    since geometry of smaller rear wheel sets saddle back, etc.?

    "theory guides, experiment decides" -- as a chemistry professor, I often use this saying with students in the lab... it's difficult to believe a 29" fork would give me the same feel, and besides, would it stress the head tube too much? I do 1 - 3 foot drops and lots of babyheads, roots, etc.

  12. #12
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    [QUOTE=rshalit]After 3.5 years of riding my Mojo, had no idea the design could be perfected... Onto my 2010 32-Talas-150 FIT/RLC/QR15 went a Stan's ZTR 355 650b wheel (w/Nevegal 27.5" x 2.1" DTC with Stan's solution) and immediately knew I'd never go back to 26" on front. I'll definitely keep the 26" wheel on rear, as I love the slight increase in rake angle and rearward saddle position, not to mention faster acceleration/less mass. As far as mass increase on front - the 650b wheel weighs the same as my 26" ZTR 355 wheel - maybe the newer American Classic 15QR hub weighs less, not sure - and the Nevegal tire adds (an unnoticeable) 80 grams more, total.

    I love the way this set-up rolls over rocks & roots, up and downhill, here on the endless, technical singletrack of SW NH. As well, the increase in rake angle makes it easier to manual, and the bottom bracket is slightly higher. I'd like to calculate how much more rubber from my Nevegal is contacting the ground around turns -- that must be significant -- another fraction of a knob? - my physics is too far gone - maybe someone has done this?

    To come up with your handling opinion with the larger frnt wheel, are you riding tech single track with a 150 setting or dropping to a 130 setting on your Talas?

    The reason I ask is that a 150 with a 650B is very slack and slow handling I would imagine

    Mojo

  13. #13
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    I'm not dropping to 130 mm (except on some long, steep climbs) - the handling is superb at 150 ! This thing about increasing "trail" and sluggish handling with 650b - there are just too many variables - there isn't a multi-variable formula that can simulate the real world of mountain biking - besides rake, wheel diameters front and rear, etc., there's rider mass and position, frame size & geometry (ie, I ride a Small Mojo), rear wheel and tire size, handlebar length & height, stem length, not to mention riding conditions & styles - drops, babyheads, manualing... you just have to get out and ride and decide. It took one ride to the local summit and down to know the 650b front/26 rear setup was for me -- the lower mass and better acceleration with 26 in rear and the seat back farther (my height puts me between a medium and Small Mojo frame size, and Gravitydropper doesn't make a set-back seatpost -- I absolutely can no longer tolerate the thought of not being able to lower and raise my seat on the fly so I have to have this; I have btw tried a Medium 26/26 Mojo and it didn't handle as well as the Small on the technical singletrack) and the rake angle with this setup is very sweet - as I said before, it manuals better. The only possible disadvantage I notice with 650b is going up over one very technical section, crawling (a necessity due to extreme technical entry just before this part), navigating simultaneously up and around a turn and over roots & rocks and preparing to turn quickly again to roll down babyheads in opposite direction, all through narrow clevis, & all this in about 10 or 12 feet distance, that I found myself having to noticeably, consciously, turn handlebars a bit more heavily in order to clean this section. I'm still not completely convinced it's the 650b - this is a very technical section which I was used to cleaning only about 80% of the time anyway (I know only two other people that have ever cleaned this section.) Perhaps I should lower the travel to 130 for this short section, but I'd have to do it far in advance as it would be unsafe to take left hand off the grip through there. (I'm waiting for blinkable/thinkable Talas and lockout controls... actually I'd be happy if Fox would make a remote lockout for this fork! Hmmm... if both the Talas AND lockout were remotely controllable, I wouldn't have room for thumb-reaches on my bars for both of those levers AND the Gravitydropper Turbo remote ...)
    Last edited by rshalit; 05-06-2010 at 07:49 AM.

  14. #14
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    Quote Originally Posted by rshalit
    I truly don't understand - your first two sentences contradict, and the first, wrt letting the air out of the fork, why on Earth would someone do that and then ride around ?? Am I missing something?
    What you could be missing is teeth.
    What people are trying to get is:
    Have you tried letting all the air out of your fork and fully compressing it to see if at bottom out the tire can hit the upper crown? You don't do this while riding, you do it in the comfort of your garage. You'd hate to find out the hard way that the tire rubs right when you land a jump, throwing you over the bars and breaking teeth.
    Derby says he has yet to see this happen to any 650b bike, but says a 2.3 could hit. And his experiment is part of some major government 650b cover-up. It didn't happen, don't ask questions or "they" will silence you.

    So, let all the air out of your fork, put weight on the handlebars until it bottoms, and see if the tire rubs the crown. Make a note of it, and put air back in your fork. Then report back here your findings.

    kthxbi
    Quote Originally Posted by Jayem View Post
    ...People thought they were getting a good fork because it was a "fox".

  15. #15
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    Derby, Do you think Ibis would release an official version of 650b, and do you think that geometry change needed? What would you change.

    I've been happy with my 650b front so far and have not done the full conversion yet due to a couple of things. 1) slight reduction on travel, not a big deal but it means I have to send the shock in and I just had it pushed.
    2) I like the 2.3 Neomoto I think it's an awesome tire, I don't want to put a smaller tire in the rear to take away traction I need.
    Thanks

  16. #16
    meh
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    why would you need to reduce travel?

  17. #17
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    Quote Originally Posted by mimi1885
    Derby, Do you think Ibis would release an official version of 650b, and do you think that geometry change needed? What would you change.

    I've been happy with my 650b front so far and have not done the full conversion yet due to a couple of things. 1) slight reduction on travel, not a big deal but it means I have to send the shock in and I just had it pushed.
    2) I like the 2.3 Neomoto I think it's an awesome tire, I don't want to put a smaller tire in the rear to take away traction I need.
    Thanks
    Don't hold your breath for an official 650b Ibis anytime in the next few years, unless they do a metal 650b bike. The HD easily clears 2.3 x 650b now with no shock mod, and so do all the 160mm travel forks. The HD's BB goes over 14 inches topped out with 650b as it does with DH tires on 26" rims, but with the deeper sag the HD should use its about right for climbing rough trail without frequent pedal strikes.

    I should start up a RP23 bottom travel limit service. It appears to be very easy to do from the pictures I've seen. I'll try to find an RP23 to test with (I run a coil shock).

    I really like the Neo-moto tires a lot too. I wish the casing was a bit tougher against sharp rock punctures, but no heavier if that is possible.

  18. #18
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    Holy Smokes...

    ...some people in this thread (face palm smiley here)

    rshalit, nice work. Been tempted to try such a mod with my 26" bike/fork as well. Nice to see it's working for you.
    "I love the bike. It's my meditation. I think I'm bike-sexual." -Robin Williams

  19. #19
    FKA Malibu412
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    Quote Originally Posted by clewttu
    why would you need to reduce travel?
    Likely to get weight forward a bit to keep the front from lifting too much when climbing. That's what u-turn forks offer.
    "I love the bike. It's my meditation. I think I'm bike-sexual." -Robin Williams

  20. #20
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    Thanks Derby, I might just go for the HD as a replacement for my Mojo build and build it 650b since the Fox, and RS fork would clear the tire anyways. The frame weight increase is less than half a pound.

    Now I wish KP makes 2.5 Neo Moto,lol

  21. #21
    meh
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    Quote Originally Posted by Malibu412
    Likely to get weight forward a bit to keep the front from lifting too much when climbing. That's what u-turn forks offer.
    was under the impression he was talking about the shock, not the fork

  22. #22
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    Quote Originally Posted by clewttu
    was under the impression he was talking about the shock, not the fork

    Talking about "trail" and "sluggish handling" = fork, I believe. Longer post, though so maybe I missed something.
    "I love the bike. It's my meditation. I think I'm bike-sexual." -Robin Williams

  23. #23
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    On a related subject..... Who's got black 650b Blunts in stock???? Everybody that I can find is out of stock....getting tired of waiting so thought I'd go ahead with a 355, but now Stan's is out too.... Whhaaaaaaaaa.... I wanna run 650b!!!!! Anybody got any suggestions for where I can find the above, or alternatives that are wide-ish & light-ish for a 170 lb rider hitting rocky trails fast and hard 5 days a week w/ 2.35 nevegal on front at 24 psi?

  24. #24
    meh
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    Quote Originally Posted by mimi1885
    I've been happy with my 650b front so far and have not done the full conversion yet due to a couple of things. 1) slight reduction on travel, not a big deal but it means I have to send the shock in and I just had it pushed.
    2) I like the 2.3 Neomoto I think it's an awesome tire, I don't want to put a smaller tire in the rear to take away traction I need.
    Thanks
    this makes me think hes talking shock

  25. #25
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    Yes shock

    Quote Originally Posted by clewttu
    this makes me think hes talking shock
    Sorry your first comment, I was not sure if it was to my comment or others.
    yes converting the rear Derby put about a quarter thin spacer on the shock that reduce just a tad of the travel, which reduce or eliminate the chance of the tire bottom out and make contact to the back of the seat post.

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