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  1. #1
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    DIY Fat Bike fork from junk

    I been hovering around the decision to build a fatbike for a couple of years, so to get me going I ordered the tyres and also 100mm rims.

    The tyres arrived and so I'm sitting around twiddling my thumbs impatiently because I have just realised I want to be riding on them right now. Then I had a brainwave - there's enough clearance at the top of most suspension forks for the width of the tyre. Cue the chop of a pair of Bombers. That didn't work, so even more impatient by now, I nipped out and bought a MIG welder to knock up a set of forks.

    Got it home and when I put it down in my shed I spotted some more old forks for sacrifice.

    This is what happened next:


    Fork chop completed by epicyclo, on Flickr" width="549">



    Drilling stress relief hole by epicyclo, on Flickr




    Fork lowers ready to put on by epicyclo, on Flickr




    Completed fork 3 by epicyclo, on Flickr

    The clamps are Giant seat clamps.



    Weight of fork by epicyclo, on Flickr


    So I've now got a rigid fork. The weight of the steel lowers is a bit high and I could cut them in half, but I figure it's better braced like that.

    Advantages of this are that I can vary the ride height to find the optimum level. I can even vary the offset by reversing the fork and swapping the lowers to the other side. (It's quite likely that this fork will be too narrow once I fit the 100mm rims.)

    So then the next step will be to make a better and lighter fork, but first I need some frame modifications to fit the fat back wheel.
    As little bike as possible, as silent as possible.
    Latitude: 57º36' Highlands, Scotland

  2. #2
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    Brilliant. Love it.

  3. #3
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    Thanks Brant.

    What would be even better would be a fatbike from your hands.
    As little bike as possible, as silent as possible.
    Latitude: 57º36' Highlands, Scotland

  4. #4
    A Surly Maverick
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    Quote Originally Posted by Velobike
    Thanks Brant.

    What would be even better would be a fatbike from your hands.
    1+ on that

    Hey well done VB

    Once you get the Fatbike bug you've got to scratch it no matter what it takes !
    A Fatback'd Lefty for who life IS a Beach

  5. #5
    Natural Born Killer
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    In the words of Darth Vader, "Impressive, most impressive".

  6. #6
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    you build and dont look back

    here is some motivation for you. these are 4 inch slicks. there are close up pics of the rear drop outs if you want.
    Attached Thumbnails Attached Thumbnails DIY Fat Bike fork from junk-b39.jpg  

    2013 mongoose Fat bike
    2012 Moonlander.

    http://undergroundvelo.proboards.com/

  7. #7
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    Quote Originally Posted by Velobike
    Thanks Brant.

    What would be even better would be a fatbike from your hands.
    Well... you'll see something pretty soon, probably before February.

  8. #8
    A Surly Maverick
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    Quote Originally Posted by brant
    Well... you'll see something pretty soon, probably before February.

    Woohoo !

    If possible please make it component swap compatable with the Pug and Alfine friendly
    A Fatback'd Lefty for who life IS a Beach

  9. #9
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    If you want it ridden in the 'Puffer, I'm available
    As little bike as possible, as silent as possible.
    Latitude: 57º36' Highlands, Scotland

  10. #10
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    Quote Originally Posted by Velobike
    If you want it ridden in the 'Puffer, I'm available
    It might well be there. If Shaggy is.

  11. #11
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    Brant if it was 1939 we would all be asking you tobuild an aircraft with a rolls royce merlin engine to save us all here in Blighty...now were all asking you to build us a fattbike frameset for our country to enjoy ourselves
    go on you know you want to!...
    Hope would make a wide rear hub for sure and we have Middleburn for cranks/possible 100mm BB, hope and DMR build,brooks saddle...its all possible here,
    just seems right a British made fatbike for our shores,and the rest of Europe, i may be looking for several in the future

    as a matter of interest how many inquire`s would you need before taking a serios interest?
    plan it...build it....ride it...love it....
    http://coastkid.blogspot.com/

  12. #12
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    What about the 100mm rims?

    It's doubtful that your 100mm rim and a Larry will fit between the lower legs. Plus, you'll have to remove the front brake to add/remove the wheel.

  13. #13
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    Figured that the 100mm rim may not work, but this is a temporary fork. I intend to build something a bit fancier/lighter once I work out what ride height and offset I prefer.

    I usually ride with bolted on wheels anyway, so removing the brake would be a doddle.
    As little bike as possible, as silent as possible.
    Latitude: 57º36' Highlands, Scotland

  14. #14
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    Quote Originally Posted by coastkid71
    Brant if it was 1939 we would all be asking you tobuild an aircraft with a rolls royce merlin engine to save us all here in Blighty...now were all asking you to build us a fattbike frameset for our country to enjoy ourselves
    go on you know you want to!...
    Hope would make a wide rear hub for sure and we have Middleburn for cranks/possible 100mm BB, hope and DMR build,brooks saddle...its all possible here,
    just seems right a British made fatbike for our shores,and the rest of Europe, i may be looking for several in the future

    as a matter of interest how many inquire`s would you need before taking a serios interest?
    This frame will be a Lynskey USA made one.

  15. #15
    That Unicycle Guy
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    Nice. Next time I am in the mall (garbage dump) I will see if I can find a suitable fork to try this with.

  16. #16
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    Impressive work, Velobike!

    Exciting news from Brant, too

  17. #17
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    Off to test it now. I'll try it at its minimum height first in the interests of testing, but then I'll lift it 50mm to 75mm. The normal ride head height is about 90mm higher usually.


    Fat Scandal side by epicyclo" width="549">
    As little bike as possible, as silent as possible.
    Latitude: 57º36' Highlands, Scotland

  18. #18
    Harrumph
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    That's a terrible hack job and probably dangerous..............

























    I love it!
    Slowly slipping to retrogrouchyness

  19. #19
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    Looks Bonkers! and brilliant!
    plan it...build it....ride it...love it....
    http://coastkid.blogspot.com/

  20. #20
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    Back from testing it. Twice. No doom befell me. No parts shifted, bent or failed.

    Quote Originally Posted by G-reg
    That's a terrible hack job and probably dangerous...
    Bear in mind that your front wheel has less clamping area and tension holding it in than I have on those fork legs.

    Handling - nice and sharp in the tight stuff also good on descents. Ran the tyre at 15lbs but I think I'll drop that lower.

    It just rides over everything. Pick a line? Why bother? It will be even better when I sort out the back wheel. That 29er RR 2.35 is just so skinny now

    I have been round the StrathPuffer course which contains most of the riding conditions you get around here. I didn't time myself, but I will not be surprised to find it equal to my 29er times, and gut feel is that it is faster because the climbs on rocky and loose stuff felt easier.

    Here's a pic at the top of View Rock just before I put my life in my hands for the descent


    Scandal at top View Rock by epicyclo" width="549">
    As little bike as possible, as silent as possible.
    Latitude: 57º36' Highlands, Scotland

  21. #21
    Single Speed Junkie
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    I like it. Really well done.

    BTW what is the tube overlap with the custom fork? I'd try to have as much as possible mitigating the risk of it folding. Once you find the optimal setting might want to consider some epoxy or red locktite bonding the two, or anti-seize if you want to have long term adjustability.

  22. #22
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    force input

    Be ginger with that hack fork. It may not slip, but those fork parts aren't designed to have any radial compression forces applied. If you were to look at a pure FEA model of a tube under compression (axially aligned) it may be fine, but there may be a finely balanced force set lurking about.
    Not saying you will run into problems, just don't plan on using this set-up long term...

  23. #23
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    There's loads of overlap. The original intention was to bond it, but I'll just use this setup to test various ride heights and offsets, and once I've found what I like I'll knock up a proper fork.
    As little bike as possible, as silent as possible.
    Latitude: 57º36' Highlands, Scotland

  24. #24
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    All this is great
    just like the early days of mountainbiking, experimenting with home brew stuff...
    then going out and seeing just what you can ride over/through,
    plan it...build it....ride it...love it....
    http://coastkid.blogspot.com/

  25. #25
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    This is great! what a brill idea. I've got some old suspension forks knocking about that are shot, I might try it with those.

    Do you reckon it would work with magnesium/alloy lowers?

    Feck it I'll give it a go, may have to wear a full face helmet and some body armour when out on the first test ride.

    Cheers

  26. #26
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    Quote Originally Posted by Mattbike
    This is great! what a brill idea. I've got some old suspension forks knocking about that are shot, I might try it with those.

    Do you reckon it would work with magnesium/alloy lowers? ...
    You may have to shim the gap between the stanchion and the lower. Old coke cans make nice precise thickness shims

    I'd be cautious about using the clamp technique on magnesium, but I see no reason why it wouldn't work if you used a bonding agent instead. Obviously you need to be sure to have everything in line and be aware you are venturing into the unknown.

    I've been looking around for a worn out pair of downhill forks. With their long stanchions and greater width, they'd be ideal for this sort of bodge, especially as the stanchions are clamped in the fork yoke.
    As little bike as possible, as silent as possible.
    Latitude: 57º36' Highlands, Scotland

  27. #27
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    If your worried about the legs slipping down/up - could you 'lock them out' with a suitable full length dowel or tube inside?

  28. #28
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    I did this with a pair of old Rockshox Psylos with mag lowers. I've had no probs with slippage (been riding it for 6 months including some gnarly stuff including rocky sections steps etc.). Two seat post clamps and some shims did the job. Don't forget one seat clamp is designed to clamp the seat post in place with whole body weight on it. With this you have 2 clamps without whole body weight on it all of the time.
    Sorry I can't post a pic but check out the Fat bike threads on singletrack world, there's a pic on there.
    Thanks for the inpiration/idea Velobike

  29. #29
    bikeboatbrewski
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    OPBTTT

    I would second the old RS fork idea, got one on my 92 Moongoose IBOC which is now a hybird. My buddy who is a frame builder told me if I ever wanted a rigid fork that it would convert no problem. I will do that one day when the forks no longer hold air.

  30. #30
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    Quote Originally Posted by scottybinwv View Post
    OPBTTT

    I would second the old RS fork idea, got one on my 92 Moongoose IBOC which is now a hybird. My buddy who is a frame builder told me if I ever wanted a rigid fork that it would convert no problem. I will do that one day when the forks no longer hold air.
    If this is a '92 rockshox Mag21 or similar model, there is insufficient clearance between the stanchion tubes to fit a fat tire.

  31. #31
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    Great idea! That's what I need for my bike! Thanks

    However I've got a question, do you used two kind of forks? One for the lower stanchion and one fot the upper part? This was done for tollerances (for blocking) between the stanchions on the original fork or what?

    Thanks.

  32. #32
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    Quote Originally Posted by bricke View Post
    Great idea! That's what I need for my bike! Thanks

    However I've got a question, do you used two kind of forks? One for the lower stanchion and one fot the upper part? This was done for tollerances (for blocking) between the stanchions on the original fork or what?

    Thanks.
    I did use 2 forks for the fork shown here, but it's quite possible with one*. Remove the bushes and make up some shims. You'll find a Coke can about the right dimension. Then epoxy is your friend.

    I'm afraid there's no perfect recipe, it is DIY after all


    *I'm about to make another with just one fork, but it will be for very short term use while I try out some theories on offset/trail.
    As little bike as possible, as silent as possible.
    Latitude: 57º36' Highlands, Scotland

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