FatBike front suspension- Mtbr.com
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  1. #1
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    FatBike front suspension

    I'm curious about the fatbike collective's thoughts on this ActionTec suspension setup (http://actiontec.us/proshock.htm). I figure it would be compatible with most forks, but have absolutely no experience with it.

  2. #2
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    They require a 1 1/4" head tube, so are not compatible with most MTB frames, and no current production fat frames. It is a neat idea, though, and if you wanted to have a custom frame built with a 1 1/4" head tube Action Tec would probably build you an extra-wide version of the fork.
    I have no idea how well they work, though.

  3. #3
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    Quote Originally Posted by intheways View Post
    I'm curious about the fatbike collective's thoughts on this ActionTec suspension setup (http://actiontec.us/proshock.htm). I figure it would be compatible with most forks, but have absolutely no experience with it.
    It is an integrated part of a custom fork. Totally doable for a fat tire.

    And you will need the custom frame to match.
    mtbtires.com
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  4. #4
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    Thanks for the replies. I don't know how doable it is, but I was considering having the headtube of my Pugsley hacked off and replaced with a 1 1/4. Ditto with the fork and suspension unit.

  5. #5
    Dr Gadget is IN
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    Waltworks used to build custom forks with these - along with the frames to match. IIRC there were issues with the bushings wearing out quickly when used seriously. If I was going to that much trouble, I'd just use a Headshok unit as the base and have frame and fork built around it.
    This isn't a "you're doing it wrong" topic.

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  6. #6
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    Quote Originally Posted by wadester View Post
    IIRC there were issues with the bushings wearing out quickly when used seriously.
    Thanks for the info. That's the kind of thing I need to know before I get too mentally invested into a project like this.

  7. #7
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    Quote Originally Posted by wadester View Post
    Waltworks used to build custom forks with these. If I was going to that much trouble, I'd just use a Headshok unit as the base and have frame and fork built around it.
    I have a customer who's having this done right now. He hacked out the guts of a Headshock for his builder to work around. I guess it was pretty simple work, just had to get over carefully hacksawing off brand new, perfectly good legs, but they are press fit/bonded onto the Headshock upper at the crown....

    Can't recall, but I do believe it's Walt who's doing the work.

    Go for it, 80mm of lock out and rebound control would be a really nice compliment to the fat front.
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    If you should want to build a fork from scratch, Magura makes (or at least use to) a hydraulic cartridge for the fatty system

    http://www.magura.com/en/products/older-products/suspension-forks-2008/prod/magura-ccs.html

  9. #9
    bikeboatbrewski
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    They should just step it up to 1.5" tubing. Still need to have the custom frame to keep the head angles where you want them. Might as well go full out and put one in the rear seat stay for the back end too.

  10. #10
    Hybrid Leftys aren't real Moderator
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    Quote Originally Posted by docBol View Post
    If you should want to build a fork from scratch, Magura makes (or at least use to) a hydraulic cartridge for the fatty system

    http://www.magura.com/en/products/older-products/suspension-forks-2008/prod/magura-ccs.html
    Don't know if they still do, and I'm not being a wanker, but those were a total flop on this side of the pond. Can't say as I'd put energy into tracking one down but YMMV.....
    This is a Pugs not some carbon wannabee pretzel wagon!!

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  11. #11
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    Here is my low budget attempt at on suspension for a fat bike. I am trying to put together a fatbike on a shoestring budget so thought I would forgo buying a fatbike fork. I found a very old manitou 1 suspension fork for $10 at local bike co-op and first thought I would use just the crown as a the basis for a fat fork. On this fork, the stanchion legs are clamped into the crown with just a couple of pinch bolts, not permanently press fit to the crown. I planned to remove the suspension legs and replacing with solid fork legs. After I tore the fork apart and analyzed it, I realized it just might be possible to re-work the manitou 1 to fit a fat tire and still work as a suspension fork.
    The two immediate obstacles are that the stock arch has insufficient clearance for a fat tire and that the entire fork needs to be extended further than stock in order to be long enough for a fat tire.

    Here is the result of my fiddling;
    FatBike front suspension-fatmanny1.jpeg

    The manitou 1 fork it really, really primitive. This was the very first fork design offered by Manitou. I now can strip it down blindfolded with just an allen wrench in about 1 minute. No comparison to modern fork performance but there are few modern forks that you could easily modify to add a taller arch since they all seem to have the two lower sliders cast together with the connector arch (or use archless design like the DUC and Lefty with proprietary hub connection). On the Manitou 1, the connector arch is just a flat piece of aluminum that bolts onto the lowers. Below is a comparison of the stock arch (left) and an arch I fabricated (right) to provide additional clearance. It is just made from a piece of 1/4" alu plate that I cut out with a hacksaw and a electric jigsaw and then drilled out to match the 4 mounting bolts.
    FatBike front suspension-fatmanny7.jpeg

    Here is a shot demonstrating clearance between fork legs and a 87mm wide Larry tire when mounted on a 44mm snowcat rim.
    FatBike front suspension-fatmanny3.jpeg


    To lengthen the fork and provide sufficient clearance between the tire and the fork crown, I used a longer skewer bolt I found from another junker shock. On the manitou 1, each of the lower legs are held onto the upper stachion tubes by a single long bolt that also retains the elastomer stack (below the stachion). By using a longer bolt, it allows the fork to extend further at rest position and allows for ability to increase fork travel beyond stock 40mm up to 70mm. The lower leg and stanchion still overlap at the two bushings by 110mm at rest, seem to still provide enough lateral stiffness.
    FatBike front suspension-fatmanny4.jpeg


    This fork originally used elastomers for the suspension spring. The original elastomers were shot and needed replacement. I intend to ride this bike during Alaska winter and elastomers have a pretty bad habit of becoming non-fuunctional when cold so I substituted a steel coil spring I sourced from another cheap junker fork to provide most of the suspension travel in place of elastomers. (Elastomers still help with the bottom-out)
    FatBike front suspension-fatmanny5.jpeg


    I actually got ahold of a couple similar manitou forks. The one I started with had the lower length of the stanchion legs externally butted . Lengthening a manitiou like I did would not work with the externally butted tubes as the butted section would need to travel past the bushing and dirt seal due to the raised travel height. I first intended to lengthen the butted stanchion tube by brazing a extension on the top (with a reinforcing sleeve) to raise it up but then I found another (even older??) manitou 1 with non-butted stanchions so it needed no lengthening modification with the longer skewer bolt I used. Comparison of the butted and unbutted stachions follows:
    FatBike front suspension-fatmanny6.jpeg


    FatBike front suspension-fatmanny2.jpeg


    Pros of this approach is that it can allow addition of suspension to a fatbike build using old junk parts for very little $. I have been riding it for a week as a 1/2 fat (conventional rear wheel) and it definitely works and provides useable suspension. With the far tire and suspension, I am able to get through severely rocky trail sections I cannot imagine getting though with a narrow tire. At just a touch over 3 pounds, it is a fairly lightweight suspension fork, does not add too much weight.

    Admittedly the Cons of this approach are numerous. The fork only works with cantilever brakes, no disks unless you were to devise a clamp to attach a caliper mounting bracket. The fork only has 45mm of rake so on my old frame designed for a shorter fork, it slackens the headtube angle probably 3 or 4 degrees, way to much resulting fork trail makes the steering less than ideal. This probably would not be so bad on a frame designed for a tall fork. The fork is laterally flexible in comparison to modern forks but it really is not too bad. Larry tire on my 44mm rim is around 87mm wide. The manitou measures 92mm between the stanchion tubes so clearance is tight, probably would not work easily with a much wider rim. However, you could probably dimple the inner side of the stanchion tubes where the tire would contact (above where the seal and bushing travel) to provide a bit more clearance if needed for wider rims/tires. Getting the tire into the fork is also a bit of effort, need to deflate to <5PSI to pinch the soft tire past the cantilever studs. Without the elastomer suspension, there is minimal rebound dampening (just dampened by bushing friction) so is a bit of a pogo- stick on big hits.

    I originally started my fork project with an old rock shox Mag 21 which also uses a crown that pinch clamps the removable stanchion tubes. Unfortunately, the early rockshox use an even narrower spacing between the stanchions that is far too narrow for a fat tire. I know some of the later RS Judy forks still used a removable arch but I have not found the dimension for spacing between the stanchions for a Judy. I would be curious to know what this measurement is for the Judy to see if perhaps it could also be adapted for a fatbike.
    I have not had my hands on a later Manitou 2,3,or 4 to see if they could be adapted either. These later forks were further development and more advanced design but may be more difficult to adapt due to other differences in stanchion butting, aluminum stanchions and different brace design?
    Last edited by GrayJay; 06-25-2011 at 08:47 AM.

  12. #12
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    GrayJay, that is some really great work !

    We all LOVE a bit of experimentation and fettling on this board , well done
    Life IS a Beach and then you Corrode :)

  13. #13
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    Quote Originally Posted by Dr Feelygood ! View Post
    GrayJay, that is some really great work !

    We all LOVE a bit of experimentation and fettling on this board , well done
    Agreed! Awesome innovation.

  14. #14
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    All the best bodgers are on the fatbike forum
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  15. #15
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    Quote Originally Posted by antpal01 View Post
    Gray Jay, thanks, Bud! I did see and read a few times your thread! I was actually trying to find a Manitou, but have not yet had any luck. If you have any suggestiosn on where to source one, please let me know!

    Also, a few other questions:
    1) Where did you get the aluminum for the custom cut out you did for the brakes? And did you need a special blade on the jigsaw?
    2) Any suggestions for getting the springs and other longer bolts used in the fork? Woudl a local shop have/ be able to order these or would I need to get them from an old shock? If old shock, any suggesitons as to the best candidate?
    3) For the longer stanchions, do you have any specifics on what model fork they came from? Seems like these are critical, and I might have a harder time finding them. (I am still new to mountain biking, so sorry if this is a silly question.)
    4) With the different rim, what is the width of the Larry? Is it the same, as say on a Large Marge or is it narrower becasue of the narrower rim?
    5) What is the total travel? Almost 4"?

    If it's easier to call me, please do so.

    thanks agian for sharing the results of the project! Awesome ingenuity! :-)

    Anthony
    973 449 3110
    I seriously doubt you will find a new Manitou Fork for sale from a regular retail source, these things are anchient and obsolete. Search e-bay for manitou forks and then sort through the results to find the earlyist ones that use the cantilver boss as one of the 2 bolts per side retaining the arch. The later Manitou 2 onward forks used an arch mounted above the brake boss, retained by two separate bolts per side (done in part to help increase overlap between the slider seals for a more ridgid fork).
    Here is an example Manitou 1 on e-bay
    http://cgi.ebay.com/MANITOU-ANSWER-E...item2a120b14c4

    Only diffuculty is that it is setup for 1" steer tube but for $15 on e-bay you can buy a 1-1/8" crown and switch out the fork legs. I am pretty sure that the pictures Manitou 1 with flat grey graphics are the ones that used non-butted stanchion tubes. The sliders with anodized colored graphics in my picture were probably from a slightly later model and did come with butted stanchions.

    1) 1/4" aluminum plate can be sourced from a welding material supply store. I used a scrap I got from a neighbor that fabricates aluminum boats. Easy to just with a regular metal hacksaw blade. For the tighter corners, an electric jigsaw with a standard metal cutting blade (from home depot) works well.

    2) the shock I robbed the springs and longer bolt from was an absolte POS junker, probably from a wal-mart grade bike. Damm fork probably weighed 10 pounds. Manufacture was too ashamed to put thier name on it so I dont really know what it was. Might also be possible to buy just the bolt from a fastener supplier but if you can dissasemble a few junker forks it gives you plenty of parts to play with. One possible source for springs is;
    http://wings-suspension.com/rockshox.html

    You can also probably just use much cheaper generic springs from a hardware store. Note that I only used a spring in one fork leg, using both of the springs I had was much too stiff but two springs would work if they were softer.

    3) see above, non-anodized version.

    4)Larry on a 44mm snowcat was between 87-88mm, I suspect that it might still be narrow enough on a 65mm rim but probably no wider.

    5) I set the travel to 70mm (just under 3") it could done with slightly more travel but would jack up the front end even more and it would be even less laterally ridgid.

    I would be very interested to hear from any other fatbike bodgers about other possible vintage forks that might make suitable fat conversions. Something with even wider inside stachion spacing (and a removeable arch) would be even more desireable.
    More idealy, it would also be possible to braze/weld togehter a custom segmented steel fork crown built with pinch clamps to retain each of the suspension legs. (Stubby little 2" fork tubes that raise up the fork height.) I have an old rockshox mag21 fork that might someday become a leg donor for such a project.

  16. #16
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    Update- after riding my fattened-up manitou 1 fork for a year now, it has held up fine and proven reliable. Great for summer trails but I have also found it very nice to have a bit of front suspension when riding winter snow after trails get hammered from hikers and moose postholing soft trails that then freeze hard and rough. Only difficulty I have had with this fork is that the stanchion seals are worn-out and ineffective so the internals can get contaminated from sand/dirt/mud/water fairly easily which causes it to develop too much friction, gets notchy feeling until I disassemble and clean it out .

    My fat manitou fork fork was made from a very early style only made through 1991 in which the cross-brace is in part bolted on by the cantilever brake bosses. I recently liberated a slightly newer manitou 2/3/4 style fork from local bike co-op. This later style of manitou fork manufactured by ANSWER was a improvement of the original 1991 design, the pretty CNC cross brace was shorter & stiffer looking and it bolted on above the cantilever bosses and positioned the upper stanchion seal and slider bushing higher for more overlap between the stanchion and lowers. I would suspect that these later style manitou forks were much more numerous and more readily available to find now than the early style.

    I took the manitou 3 (hereafter M3) fork apart and found that it was even easier to modify for fat use than the early style. The M3 style fork moved the elastomer stack from below the stanchion tubes (as in the manitou 1 forks) up inside top of the stanchion tubes. My M3 fork had the elastomers replaced long ago with steel coil spring (coil spring location is same as the elastomers.) The M3 fork uses a long, thin plastic resin spacer tube that runs from just below the spring stack, down to bottom of the fork lower slider. Modifying the fork internals just involved shaving a top-out spacer off the plastic tube (allows the fork to extend further to accomidate fat tire), adding a spacer below the coil spring or elastomer stack to make the spring stack effectively taller for more extension (I added an extra piece of elastomer as spacer). The bottom-out for the fork is controlled by a round metal clip with a u-shaped cutout, this clip slips into slots on the plastic spacer rod below the stanchions. Just needed to cut a couple of new slots in the plastic rod to position the clip up higher, so that bottom-out occurs before fat tire contacts the fork crown. All the internal modificaions take no more than a hacksaw and file to perform and there is no need to chase down parts from several forks as I originally did on the manitou 1.

    FatBike front suspension-img_5808.jpg

    FatBike front suspension-img_5809.jpg

    The manitou 3 fork came with a very nice looking CNC fork cross-brace, unfortunately it cannot be used fat, too short for fat tire. It would be fairly easy to fabricate a new bolt-on brace as I did with my fat manitou 1 fork, but I noticed that the original fork brace from the manitou 1 was tall enough the clear the fat tire on the manitou 3 which has the brace mounting location higher. The outer bolt holes in the M1 brace and the M3 fork lined right up, brace holes just needed to be beveled/countersunk to match the beveled M3 mounting screws. The inner M3 brace mounting holes are further apart compared to the M1 brace but I was able to drill and countersink new holes in the M1 brace so it bolted right up to the M3 fork. The OEM M1 brace I used on the M3 is stiffer and nicer looking than the brace I fabricated from aluminum plate for the M1 fork, and modifying the M1 brace was much simpler than fabing an all new brace to suit the M3 fork. Picture below shows both the M1 and M3 style braces.

    FatBike front suspension-img_5810.jpg

    I've ridden the fat M3 fork now for a week and it works great. Seems that it is perhaps a bit stiffer and it has aluminum stanchion tubes (M1 were steel) so is a bit lighter. No catastrophic failures yet from my test-riding. Same 92mm spacing between inside of the stanchion tubes so it wont clear a 3.8" tire on a rim any larger than 45mm. Still restricted to just cantilever brakes, no disks though there are a few rare examples of M4 forks that did come with mounts for early sachs disk calipers (not current ISO mount compatable).
    Last edited by GrayJay; 08-15-2012 at 03:13 AM.

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