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PostPosted: Wed Jan 30, 2013 6:08 pm 
MacRetro rider
MacRetro rider

Joined: Fri Feb 09, 2007 4:16 pm
Posts: 8661
I plotting a home built sand/snow bike, not an alrounder like a true fat bike just an experiment in floatation cycling, already ordered some wheels and tyres. The wheels are 4" diameter lawnmower wheel rims shod with 3" cross section baloon tyres giving 10" total diameter. Thats stoopid you say and yes your probably right but I can in theory fit 3.5" high x 11" wide tyres to this rim which are still reasonably round profiled with a huge footprint. Will require bolting a very wide fork arrangement to an existing frame and elevating said frame plus lots of tortuous drive chain routing but all that looks fun. Dont expect any quick progress but do expect one ugly barsteward of a bike.

These are the cheapo wheels
http://www.northerntooluk.com/tyres-and ... 3431E.html

and these are the tyres I might be able to fit
http://www.allterraintyres.co.uk/index. ... s_id=90414

I haven't done anything this stupid since I coverted a mixte framed road bike to a short wheelbased recumbent using bits of wood and a cut up old mtb frame. Was doing great untill the pedal boom snapped right in front of a bus shelter full of jeering laughing teenagers :oops:

Keep you posted :wink:


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PostPosted: Wed Jan 30, 2013 8:00 pm 
MacModerator
MacModerator
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Joined: Fri Jul 14, 2006 8:59 pm
Posts: 20774
Location: Sol Kitts
Go for it Velo! Have you saw anything like this done before or are you winging it? I take it the hannebrink bikes are the inspiration? Oh and if I can help you with any fab work just holler!


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PostPosted: Wed Jan 30, 2013 9:35 pm 
Gold Trader / MacRetro rider
Gold Trader / MacRetro rider
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Joined: Mon Feb 11, 2008 12:03 pm
Posts: 5126
Location: held captive by baby haggis in a cave in Scotland
Here's some inspiration for you Velo!
Sounds like a challenge but I'm sure you'll get it done.
Cheers
Jamie

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PostPosted: Thu Jan 31, 2013 10:27 am 
Retro Guru
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Joined: Tue Sep 21, 2010 8:08 pm
Posts: 1939
Location: East Lothian
Looks like the new Surly 2014 prototype to me.


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PostPosted: Thu Jan 31, 2013 10:43 am 
MacRetro rider
MacRetro rider

Joined: Fri Feb 09, 2007 4:16 pm
Posts: 8661
Hanebrink is my inspiration but i have seen home bodged afairs on the web and once a site for hiring bikes in some foreign resort where some of the fleet were purpose built versions of what i propose. It will not be a 29er equivalent fat tyred mtb like a pugsley, it will not have the ability to roll over anything but hopefully it wont sink in soft sand so some beach cruising can be had 8)
Thinking for Mk1 i'll stick to 4 inch wide tyres, it seems I might be able to use some mini moto cross components such as 4.1" wide tyres, brake discs and sprockets.


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PostPosted: Thu Jan 31, 2013 12:01 pm 
MacRetro rider
MacRetro rider
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Joined: Fri Mar 09, 2007 2:11 pm
Posts: 8700
Location: DUNDEE
If you are using that size of wheel Velo there are plenty of tyre options from the kite buggy scene.

How are you going to implement the drive?


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PostPosted: Thu Jan 31, 2013 1:45 pm 
MacRetro rider
MacRetro rider

Joined: Fri Feb 09, 2007 4:16 pm
Posts: 8661
Wheel rims come in two halves bolted together by 4 bolts. i plan to replace bolts with threaded rod out to beyond the tyre width with spacers and bolt a plate to each end. May need several plates between wheel face and outer plate to prevent tortional twisting of bolts. On the plate i will bolt via spoke flanges the ends of hubs minus the hub barrel or internal bearing cups. Plan to use large flange disc brake 6 bolt donor hubs. Bolt a fixie bolt on sprocket to this and run chain up left hand side of wheel to another uncut up rear disc brake hub mounted in frame dropouts using another bolt on fixie sprocket. Then the primary drive can run from chainset to cassette in usual manner. i f I go for tyres wider than chainline allowance for a 135mm rear hub there will be more bodging. No guarantees any of this will work but should be fun.
Currently 11 inch diameter tyres look tiny but posses a width equal to on-ones new 4" wide fatbike tyre. :lol:


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PostPosted: Thu Jan 31, 2013 2:02 pm 
MacModerator
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Joined: Fri Jul 14, 2006 8:59 pm
Posts: 20774
Location: Sol Kitts
Couple of suggestions V, rather than rod try to get some threaded hex bar, it will be alot stiffer than screwed rod. Also have you considered a BMX large flange hub? For what your suggesting the slots in the large flange could be utilised and you would also have the ability to fir a freewheel. If you are going to go fixed why use a hub at all? You could bolt the fixed cog straight to the plate at the end of the screwed rod/ hex bar? I take it you 'cold set' a steel frame for dropout size?


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PostPosted: Thu Jan 31, 2013 2:15 pm 
Gold Trader / MacRetro rider
Gold Trader / MacRetro rider

Joined: Thu May 21, 2009 11:02 pm
Posts: 5253
Location: Falkirk! But I am a Fifer so that's OK...
He's only going fixed on LHS from the rear cog to the intermediate hub mounted part way up the chainstays? Free hub on RHS to rings as normal - options would be singlespeed sprocket plus spacers or cassette and some sort of derailleur bodge?

Although BMX freewheel and cranks/ring mounted on LHS would negate need for intermediate hub?

Really interesting though, looking forward to seeing how this goes and how the challenges are addressed.


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PostPosted: Thu Jan 31, 2013 2:22 pm 
MacRetro rider
MacRetro rider

Joined: Fri Feb 09, 2007 4:16 pm
Posts: 8661
Good suggestions, i shall think on those. Currently I could fit the wheel into a frame directly but locate a BB shell higher up on the frame to give pedal ground clearance, basically reduce the seat to BB distance on say a 22" frame then make up difference with longer seatpost.
I reckon with pointers from the web I could coldset a steel frame beyond its design spec, can make minor adjustments already, but not sure i want to just yet.
Cheers


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