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Discussion Starter · #1 · (Edited)
Current Issues in this Thread:

Rear Cassette: I'm looking for something with 3-6 cogs. I need something that will allow the cogs to be spaced out a lot! My dropouts are about 175mm wide.

DH Bash plate and Chain guide: I'm planning on fitting a bash plate, and possibly DH style chain guides. But I'm not sure how this would work/fit the crank sought after above?

Intro:

I'm building a fatbike and on this downhill frame:
Bionicon Ironwood

Bicycle tire Wheel Bicycle wheel Bicycle wheel rim Bicycle part


The purpose of this bike will be purely downhill riding, probably on ski slopes ;) Other than that I just want it cheap as possible. So Weight is of zero concern.

It has a two piece swingarm, Pics Below, so I'm figuring out how to widen the pivot with spacers. I will post pics of the pivot when I can.


Swingarm Pictures:


In first pic you see on the upper ride corner of the Swingarm(black part), is the Shock Mount, below that is the Large Stiffener tube, and below that is the Pivot, Towards the left side of the Swingarm, stuck to the bottom is the Small Stiffener:

Bicycle accessory Bicycle part Metal Composite material Aluminium


Blue Bicycle accessory Bicycle part Carbon Azure




Bearing Cups sitting in frame tube:
Blue Azure Electric blue Cobalt blue Plastic


Pivot axle and bearings:
Finger Nail Thumb Engineering Steel



Parts List:

Have a shot at adding to/editing my parts list.

Rear Swingarm:

  1. Wide Shock bolts and spacers
  2. Wider Stiffener tube
  3. remove small stiffener tube close to tire
Rear Swingarm Pivot:

  1. Bearing Cup spacers,
  2. Stiffener to hold spacers for the Bearing Cups in place,
  3. Pivot Axle stiffener,
  4. 5/16?" All thread to clamp the whole Pivot Axle together.
Fork: ? rebound adjustable would be nice

  • Risse Trixxxy, Specs: 7" Travel, tire size 26" x 4.8", Overall Tire diameter 30.8", max casing width 121mm,

  1. intl brake mount,
  2. fork guards or boots?
Rear shock:

  • Risse Astro-5, Specs: set for downhill riding, strong rebound/light damping for heavy wheel + DH swingarm,

  1. bushings for eyelets,
  2. boot
  3. hardware.
tires/tubes:

  1. Surly 4.8s
  2. tubes: Surly toob? Anything tougher out there?
  3. ultra low pressure/run flat System?: two 26x1" foam tubes (bell no mor flats) on each wheel.
Headset: standard zero stack 44mm (ZS44 standard), second hand.
Brakes: mechanical discs, ~200mm rotor, floating? Most bang for the buck?
hubs: already have 160mm rear and 120mm front
wheels: the toughest 80mm wide wheels? Surly Marge?
bottom bracket: 73mm wide shell. Whats the widest spindle? cotterless candidate
cranks: Drive side crank that places gear further out, otherwise second hand.
Bashplate/chain guides: DH style chain guide and Bash plate compatible with Cranks, for biggest possible front Gear.
Front cog: Largest possible, second hand

Rear derailleur: second hand

cassette: second hand

chain: second hand
Brake Levers: second hand
Shifters: second hand
4' brake housing: second hand
pedals: second hand
seat post: second hand
stem: second hand
handlebars: second hand
 

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I'm going to be following this with interest. I've being eyeing off Bionicon at the local dealers for the last year. It looks ideal for a fatty conversion. Be good if you can use the Bionicon front fork and the integrated system.
 

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A few things:

The Trixxxy fork doesn't have much clearance. No way 4.8" tires will fit. On the Carver Trans Fat they have on their site, clearance is tight with a 3.8" tire on a Marge Lite: Carver TRANS-Fat Full Suspension Fat Bike

Adding fat tires to a 26" wheel bike is going to raise the bottom bracket and standover. Probably won't be an issue for what you plan to do with it.

I would not remove the stiffener tube in front of the rear tire if at all possible. You are increasing the sideways leverage on the rear triangle quite a bit by increasing tire diameter, and your spaced-out pivot and shock bolts will be weaker than stock.
 

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not FAT free
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high bb on fs fat bike is not a big problem
my bb is 16" high and bike looks high but suspension is set plush so when it sags it's not 16" anymore
from my experience - no worries

as far as stiffener removing -- i agree with Andy, You should leave it
if that is 26" wheel frame i think You are facing rear dropout mod to move axe out for needed clearance
if You want to remove stiffener to get clearance than probably tire will have contact with seat tube and You will end up with shortening travel - which is nonsense imho
cheers and keep going !!
subscribed :)
 

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Discussion Starter · #5 · (Edited)
I'm pretty excited about this build! RFX Big foot I remember reading some of your build thread when I was whipping up this idea. Did you have a trixxxy fork? I need to know the clearance for the tire width... if it can't fit the 45nrth dillinger 4" tires this fork is a no go. In which case I don't know what to do because the German A flame is only 130mm travel and $1500+... Fork ideas? Andy this might be a picking on a detail but that description about the trans fat only says 100mm rims are a no go... just cling on to hope I guess

Swingarm Stiffness: I might have to do some custom dropouts to move the rear wheel back a bit, in this case I would probably set it up with some heavy duty rear axle to give me stiffness. A much beefier "Large Stiffener" (above the pivot) could also make up for removing the Small Stiffener. Otherwise I would swap the stock small stiffener with a bent stiffener, not sure how I would do that though.

Seat tube clearance: Again maybe custom dropouts... Unless I can get away with just dropping the suspension a bit, then letting it sag a lot when I sit on it.
 
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Sandman is also testing a soon to be released fat fork which I believe mimics the Flame A unit but no idea of cost comparison.
 

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Contact Risse and ask about clearances. As I recall they had made some wider clamps for the Trixxxy at one point. White Bros. also had some wider clamps for their Groove forks, so they would be worth contacting too.

Sandman is testing a new fork, but it is very similar to the German-A and the price is not a whole lot lower.
 

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not FAT free
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I'm pretty excited about this build! RFX Big foot I remember reading some of your build thread when I was whipping up this idea. Did you have a trixxxy fork? I need to know the clearance for the tire width... if it can't fit the 45nrth dillinger 4" tires this fork is a no go. In which case I don't know what to do because the German A flame is only 130mm travel and $1500+... Fork ideas? Andy this might be a picking on a detail but that description about the trans fat only says 100mm rims are a no go... just cling on to hope I guess

Swingarm Stiffness: I might have to do some custom dropouts to move the rear wheel back a bit, in this case I would probably set it up with some heavy duty rear axle to give me stiffness. A much beefier "Large Stiffener" (above the pivot) could also make up for removing the Small Stiffener. Otherwise I would swap the stock small stiffener with a bent stiffener, not sure how I would do that though.

Seat tube clearance: Again maybe custom dropouts... Unless I can get away with just dropping the suspension a bit, then letting it sag a lot when I sit on it.
what i use is White Brothers DH2 ( GROOVE is 10mm narrower still can take fat tire but not as god as older forks )
You may also use dh2, dh3, dh2.0 there is plenty of clearance for nate on 80mm rim in mud
i have no idea how wide trixxy is but it runs 120mm wide hub also so i think should be very close
best way is call Kevin Risse 541 5267242

lou fit on 80mm rim but is to tight to use usd fork have flex so under cornering and braking it would rub !
i've had no time to try lou on 65mm rim , i guess it would bring more clearance but i think not enough
cheers
 

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Discussion Starter · #11 · (Edited)
best way is call Kevin Risse 541 5267242
That sounds good... he seems pretty bad with emails.
Nice pics! you ever think of shaving the nobs slightly and filing the fork wall slightly hehehe (...sure its inadvisable)

I will be email groove brothers, that is one place i haven't searched at all.
 

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Discussion Starter · #13 · (Edited)
Contact Risse and ask about clearances. As I recall they had made some wider clamps for the Trixxxy at one point. White Bros. also had some wider clamps for their Groove forks, so they would be worth contacting too.

Sandman is testing a new fork, but it is very similar to the German-A and the price is not a whole lot lower.
Well no wide clamps from Groove Brothers... If I could get some drawings or a CAD file for some clamps I could probably get them machined at some online machine shop like: CNC Machine Shop | Custom Waterjet, Plasma, Laser Cutting | eMachineShop.com

Bottom Bracket: Anyone know of some real low priced ones wide enough to make the chain clear a 4.8" tire? I'm going with one cog in the front and I am willing to sacrifice cogs in the rear if it means I could use a more widely available BB that I might be able to find second hand.
 

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TMS in France used to make a very wide ISIS BB.

In a 68mm BB you'd have clearance for a few gears - not sure how many. I've got one in my workshop, I'll measure it up later.

Otherwise by going for an old fashioned cup and cone square taper with separate spindle, you can get a wide enough chainline. If you're just using it for downhill this should present no problems. In the UK you can get these parts from http://www.sjscycles.co.uk/cotterless-axle-7r-134mm-prod22175/. They have a 134mm axle which should do the trick.
 

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Well no wide clamps from Groove Brothers... If I could get some drawings or a CAD file for some clamps I could probably get them machined at some online machine shop like: CNC Machine Shop | Custom Waterjet, Plasma, Laser Cutting | eMachineShop.com

Bottom Bracket: Anyone know of some real low priced ones wide enough to make the chain clear a 4.8" tire? I'm going with one cog in the front and I am willing to sacrifice cogs in the rear if it means I could use a more widely available BB that I might be able to find second hand.
It's WHITE Bros., and the Groove is the fork model. A few years ago they had some extra-wide clamps they made for the Groove. There was a thread here about it. Maybe they sold them all since then, or maybe you just didn't talk to the right person.
 

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not FAT free
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It's WHITE Bros., and the Groove is the fork model. A few years ago they had some extra-wide clamps they made for the Groove. There was a thread here about it. Maybe they sold them all since then, or maybe you just didn't talk to the right person.
those wide crowns were just stock crowns made for fork ( not something special ) and they were 120mm spacing - because they thought DH will go in this direction , there was no wide or narrow option , all upside down WB forks till 2005 were 120 spacing, DH 2.0 was last model with 120mm, when they change spacing to 110mm they changed name to GROOVE so older models - UD 150 etc.. and DH2, DH3, DH2.0 are 120 mm
cheers
 

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Discussion Starter · #18 ·
Good stuff chaps, I will look further into the white bros situation. That was just a typo before, I meant white bros.

...
Otherwise by going for an old fashioned cup and cone square taper with separate spindle, you can get a wide enough chainline. If you're just using it for downhill this should present no problems. In the UK you can get these parts from http://www.sjscycles.co.uk/cotterless-axle-7r-134mm-prod22175/. They have a 134mm axle which should do the trick.
This sounds kinda like the thing for me! I should be able to find something similar at the old bike parts stores here. I just gotta figure out the diameter of the shell, he said it was "standard"...

The other thing I was wondering is if I could install some kind of chain guide like most DH bikes. Or if it will need special cog/crank/whatever. I'm definitely installing a bash plate.
 
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