2WD Christini Fatbike- Mtbr.com
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  1. #1
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  2. #2
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    Neat idea, just not sure how necessary 2WD is. As long as it isn't *hurting* her (w/added weight or drag) then no reason not to have it.

    But, in the past it has proven anything but dependable in the snow applications I've seen it used for.

    Marge lite with a 4" tire? I think a 100mm rim with a 5" tire would do a lot more to keep her riding than 2WD.

  3. #3
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    Looks nice, sounds nice ... But there's a reason this idea has been around for decades, and not universally adopted.

  4. #4
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    But on snow and fat it might make more sense than ever.
    No it never stops hurting, but if you keep at it you can go faster.

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    As a special novelty, you might be right,
    And,
    I might be wrong,
    But I expect the front drive will be disengaged/removed, before the adventure is completed.


    I'm with mikesee ... A wider tire makes more sense than 2WD and it's complexities.

  6. #6
    bigger than you.
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    They're not far from me, I may have to ride over and talk to Steve.
    Last edited by Gigantic; 04-13-2013 at 07:08 AM.

  7. #7
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    Quote Originally Posted by mikesee View Post
    Neat idea, just not sure how necessary 2WD is. As long as it isn't *hurting* her (w/added weight or drag) then no reason not to have it.

    But, in the past it has proven anything but dependable in the snow applications I've seen it used for.

    Marge lite with a 4" tire? I think a 100mm rim with a 5" tire would do a lot more to keep her riding than 2WD.
    I have often wished for a Christini 2WD snow bike for the snow conditions we have around here. And I have one of Christini's standard 2WD MTBs, so I know how the system performs.

    I'm not sure if I would want the extra complexity and maintenance on something like an Antarctic expedition. But, I don't do stuff like that.

    What other snow applications have you seen 2WD used for?

  8. #8
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    I test drove one of the original bikes a dozen (or more?) years ago at a mountain bike fest in Jim Thorpe, PA. It does work, and helped noticeably when climbing in loose dirt. As I recall, there was some drag. I always wondered what would happen if you were going fast downhill and skidding the rear wheel while the front was still rotating.

  9. #9
    How much does it weigh?
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    The front wheel freewheels forward if it's like the 2WD bike I've wrenched on.

  10. #10
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    they say the differential in gearing causes the front wheel to not be driven under normal riding. If this is true, the front wheel must be underdriven, and allowed to freewheel with a one-way clutch of some kind, so only if the rear wheel speed increases or the front wheel speed decreases, will torque be transferred.

    In the case of loss of rear wheel traction when braking, the front wheel is still overrunning the clutch, so no torque is transferred.

    On the other hand, if the front wheel skids under braking, the rear wheel will try to turn the front wheel, effectively delaying the skid until rear traction is overcome as well. But, then both will skid. It would have to be pretty darn slippery to do so, though.

    Since the front wheel is more important for steering, this works to improve control under braking at near the limit of traction.

  11. #11
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    She'd probably ride a custom Wall-Goose if they help pay for the expedition costs...

    I bet she's not all that concerned about 2WD vs. RWD.
    Safe riding,

    Vik
    www.vikapproved.com

  12. #12
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    which is more likely the case?

    did they build the bike to justify the expedition?

    or

    are they funding the expedition to justify the bike?

  13. #13
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    Quote Originally Posted by autodoctor911 View Post
    which is more likely the case?

    did they build the bike to justify the expedition?

    or

    are they funding the expedition to justify the bike?
    Their technology exists so applying to a fatty isn't a big deal. This expedition is kind of ideal as marketing. It's not a race so performance isn't being evaluated, but if she makes it a Christini will always be the first bike to the S. Pole.

    Even if the 2WD packs it in after km 20 or she disconnects it and keeps riding who would know if she doesn't say anything? Low risk for Christini.
    Safe riding,

    Vik
    www.vikapproved.com

  14. #14
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    comment on Op's link:
    "Mike - 04/12/13 - 5:54pm
    Turbine wides on a south pole fatbike, sweet!"

    what are turbine wides?

  15. #15
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    Quote Originally Posted by autodoctor911 View Post
    comment on Op's link:
    "Mike - 04/12/13 - 5:54pm
    Turbine wides on a south pole fatbike, sweet!"

    what are turbine wides?
    The Race Face crank.

  16. #16
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    Quote Originally Posted by autodoctor911 View Post
    they say the differential in gearing causes the front wheel to not be driven under normal riding. If this is true, the front wheel must be underdriven, and allowed to freewheel with a one-way clutch of some kind, so only if the rear wheel speed increases or the front wheel speed decreases, will torque be transferred.

    In the case of loss of rear wheel traction when braking, the front wheel is still overrunning the clutch, so no torque is transferred.

    On the other hand, if the front wheel skids under braking, the rear wheel will try to turn the front wheel, effectively delaying the skid until rear traction is overcome as well. But, then both will skid. It would have to be pretty darn slippery to do so, though.

    Since the front wheel is more important for steering, this works to improve control under braking at near the limit of traction.
    There is a one-way silent clutch in the Christini front hub.

  17. #17
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    Quote Originally Posted by Andy FitzGibbon View Post
    There is a one-way silent clutch in the Christini front hub.
    Ah, I was looking for it on their website,and couldn't figure out where they put it. It makes sense there, maybe just a silent clutch like on a IGH has.


    I noticed it also has a manual clutch right at the rear gear drive to diconnect the drive mechanism from the rear hub via a thumb shifter arrangement.

  18. #18
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    I'd like to try climbing a packed snow hill on a 2WD bike. Several times this winter I'd instinctively stand and lean forward while climbing, unweighting the rear tire causing it to spin out. Not leaning forward would give me the sensation that any second I could flip over backwards.

  19. #19
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    Quote Originally Posted by autodoctor911 View Post
    they say the differential in gearing causes the front wheel to not be driven under normal riding. If this is true, the front wheel must be underdriven, and allowed to freewheel with a one-way clutch of some kind, so only if the rear wheel speed increases or the front wheel speed decreases, will torque be transferred.

    In the case of loss of rear wheel traction when braking, the front wheel is still overrunning the clutch, so no torque is transferred.

    On the other hand, if the front wheel skids under braking, the rear wheel will try to turn the front wheel, effectively delaying the skid until rear traction is overcome as well. But, then both will skid. It would have to be pretty darn slippery to do so, though.

    Since the front wheel is more important for steering, this works to improve control under braking at near the limit of traction.
    it's all truth
    i was testing my awd christini in a few conditions
    it is great if You want accelerate and step hard on pedals on loose dirt, wet dirt, loose gravel ,awesome on ice with studded tires , felt good on fluffy dry snow, rolls over logs and big rocks very good
    this system is more efficient on middle ring,
    i was hoping it would be very helpful on steeper climbs on snow but when i dropped to granny gear than it becomes less efficient because more than half of crank stroke was spent for slip of rear to get front in motion and whatever was left from crank stroke was not enough to pull bike and make climb
    i tried same hill many times and didn't get any further up with awd on than when awd was off (on granny gear )
    i don't see myself doing climbs on a middle ring on deeper snow
    it work great in very specific conditions and i could tell it helped me in many situations

    some time ago i started my christini fs mod and after test on regular awd christini it cooled me down a bit, but i think i will do it
    i wish it could be 1x1 so i could use it on steep slow climb or not packing dry snow etc. trading more drag for much better traction and turn it of when not needed

    my idea was to use lou on 100mm rim as front wheel and nate on rear on 100mm rim
    that setup creates difference in height of wheels and rear smaller wheel will spin faster so will keep front engaged sooner than standard setup
    the only problem is that will interfere with steering because top tube shaft transfer power to fork via gears
    if it will get to close to 1 x 1 Steve Christini told me it will be impossible to ride

    before i will drop heavy coin for cnc crowns , and dropouts and other parts i will wait to see how much Steve Christini will ask for his rigid awd and maybe this one has modified gear ratio rear to front ?

    btw Steve Christini is great person ! and i'm amazed how his awd bikes are done
    i'm glad to see his project reborn !

    cheers
    Attached Thumbnails Attached Thumbnails 2WD Christini Fatbike-dsc_0752.jpg  

    2WD Christini Fatbike-dsc_0758.jpg  

    2WD Christini Fatbike-dsc_0759.jpg  

    2WD Christini Fatbike-dsc_0750.jpg  

    2WD Christini Fatbike-02.jpg  

    2WD Christini Fatbike-04.jpg  

    2WD Christini Fatbike-07.jpg  

    Last edited by RFX big foot; 04-12-2013 at 11:24 PM.

  20. #20
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    RFX, you might be able to experiment with front-to-rear gearing by changing sprocket tooth count on the chain inside the fork crown. Not a lot of room to play around, but you might get a sense of how it would perform with a closer ratio.

    What you've done to your Christini is exactly what I was visualizing doing to mine. One of the things I was worried about was the driveshaft angle from the rear triangle to the top tube. I remember thinking that the increased operating angle of the u-joints might lead to some "pulsing" of the front drive.

    You are right about Steve Christini, he has always been really friendly and helpful in all the years I've had my FS 2wd.

  21. #21
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    Quote Originally Posted by Andy FitzGibbon View Post
    RFX, you might be able to experiment with front-to-rear gearing by changing sprocket tooth count on the chain inside the fork crown. Not a lot of room to play around, but you might get a sense of how it would perform with a closer ratio.

    What you've done to your Christini is exactly what I was visualizing doing to mine. One of the things I was worried about was the driveshaft angle from the rear triangle to the top tube. I remember thinking that the increased operating angle of the u-joints might lead to some "pulsing" of the front drive.
    You are right about Steve Christini, he has always been really friendly and helpful in all the years I've had my FS 2wd.
    Yes Andy, You are right, this sprockets are the only place to try it with lowest costs, that crown You see on my project has more space around sprockets than original so for sure i will try.
    Rear triangle is from long travel frame and is 1/2" shorter + as You see on photo - rear is moved back a lot for tire clearance which relaxed angle and is not bad when compared to original so no worries there,
    it is hard on budget project - i don't have a friend who is machinist so no easy way
    cheers

  22. #22
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    Quote Originally Posted by RFX big foot View Post
    Yes Andy, You are right, this sprockets are the only place to try it with lowest costs, that crown You see on my project has more space around sprockets than original so for sure i will try.
    Rear triangle is from long travel frame and is 1/2" shorter + as You see on photo - rear is moved back a lot for tire clearance which relaxed angle and is not bad when compared to original so no worries there,
    it is hard on budget project - i don't have a friend who is machinist so no easy way
    cheers
    Using a FS frame should allow more rear tire clearance than the hardtail frame, because the driveshaft allows the seatstay to be farther outboard. On the HT frame, the driveshaft is a straight shot to the headtube. I just got an email from Steve saying that the rear clearance on the HT frame is around 4", so that most likely rules out BFL or Bud on wide rims.

    The bikerumor shots of the South Pole bike show a BFL on the front and a HuDu on the rear, like you were talking about in your post above- so your idea should work, or at least should be rideable.

    Steve says that there will be a suspension fork option for the bikes- so you should be able to use that, instead of having a crown custom made.

  23. #23
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    I am shocked those things don't use a flexible drive shaft!
    Whatever floats your bike, dude

  24. #24
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    Came across this today.

    Weird Bike Stuff

    Check out the 'Legacy' Snow Bird half way down the page.

    http://www.sonic.net/~ckelly/Seekay/legacy5.jpg

    Also some Alenex stuff for VB and MT
    Life IS a Beach and then you Corrode :)

  25. #25
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    Lots of great reading there...Thanks Doc!

  26. #26
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    Quote Originally Posted by Dr Feelygood ! View Post
    Came across this today.

    Also some Alenex stuff for VB and MT
    I've described the Alenax as not that great to ride, but I did leave my sons lagging behind when I rode it with them - they were on 29ers. (This was in Bunya Forest in Queensland)

    If you can get used to the system, I think it would be ok.

    It's probably the answer to the Q factor problem once we get 8" tyres.
    As little bike as possible, as silent as possible.
    Any bike, anywhere, anytime.
    Latitude: 5736' Highlands, Scotland

  27. #27
    A Surly Maverick
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    It was a crazy read

    I've just noticed that there is a SECOND page !!!

    Weird Bikes II

    That 'Hydrobike' looks a little familiar Drew !

    http://www.sonic.net/~ckelly/Seekay/HydroCycle_1.jpg
    Life IS a Beach and then you Corrode :)

  28. #28
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    I always wondered if a different pedal motion could be more efficient. I guess since they have tried a few, and none have caught on, there isn't any performance advantage though.

    Oh, and I will be getting one of those exycles for my girlfriend. It says it will increase your breast size without silicone.

  29. #29
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    Quote Originally Posted by autodoctor911 View Post
    I always wondered if a different pedal motion could be more efficient. I guess since they have tried a few, and none have caught on, there isn't any performance advantage though.....

    The Alenax action takes some getting used to, but if you weren't used to rotary pedalling, it would probably be ok.

    Using a wire drive may even work for the 2WD.
    As little bike as possible, as silent as possible.
    Any bike, anywhere, anytime.
    Latitude: 5736' Highlands, Scotland

  30. #30
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    Quote Originally Posted by Dr Feelygood ! View Post
    Came across this today.

    Weird Bike Stuff

    Check out the 'Legacy' Snow Bird half way down the page.

    http://www.sonic.net/~ckelly/Seekay/legacy5.jpg

    Also some Alenex stuff for VB and MT
    Paging Rube Goldberg...

  31. #31
    A Surly Maverick
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    Life IS a Beach and then you Corrode :)

  32. #32
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    We discussed 2wd systems here a while ago, i remain sceptic!

  33. #33
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    Quote Originally Posted by Dustin Mustangs View Post
    I am shocked those things don't use a flexible drive shaft!
    Originally they did - but the flex shaft rubs the inside of the housing pretty much full length, vs solid driveshaft with bearing support. Much more drag with flex.
    This isn't a "you're doing it wrong" topic.

    WSS/OSS: Open Source Sealant

  34. #34
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    I have always been interested in Christini's AWD system, but thought they had gone away from bicycles. They have applied the system to motorcycles, still not overwhelming demand but still in business. The system does indeed underdrive the front at 80% for the moto - so you need 20% wheelspin to activate it. Not a problem with a moto, but some users change the ratio by swapping front chain sprockets. The bicycle system doesn't seem so easily changed due to the spiral bevel drive system - maybe in the head drive? The moto also has to use dual driveshafts to the front wheel to prevent torque steer, apparently not a problem with pizza power.

    Ya'll that have a Christini bicycle - what is the % front drive? Put it in a workstand, rotate the rear wheel one full turn and see how far the front rotates?
    This isn't a "you're doing it wrong" topic.

    WSS/OSS: Open Source Sealant

  35. #35
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    Quote Originally Posted by wadester View Post
    I have always been interested in Christini's AWD system, but thought they had gone away from bicycles. They have applied the system to motorcycles, still not overwhelming demand but still in business. The system does indeed underdrive the front at 80% for the moto - so you need 20% wheelspin to activate it. Not a problem with a moto, but some users change the ratio by swapping front chain sprockets. The bicycle system doesn't seem so easily changed due to the spiral bevel drive system - maybe in the head drive? The moto also has to use dual driveshafts to the front wheel to prevent torque steer, apparently not a problem with pizza power.

    Ya'll that have a Christini bicycle - what is the % front drive? Put it in a workstand, rotate the rear wheel one full turn and see how far the front rotates?
    Torque steer on the Christini bike is fairly noticeable in greasy mud- not so much in any other terrain I've had it in. I'd guess that two shafts (like the motos) would handle better, but was ruled out in favor of saving weight.

    On mine, for a full turn of the rear wheel, the front rotates 29 of the 31 spaces between the spokes- so I'm going to say somewhere around 90-95 percent.

    Rokon 2WD motorcycles, which have been made since the '60s, don't have the front wheel underdriven. They have an overrunning clutch in the driveshaft that powers the front wheel. When the forks are turned (and the front wheel starts revolving faster) the clutch allows enough slippage to prevent binding.

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