The problem I considered was one of drive train alignment. With the fat tire, the chain had to shift too far outside of the normal bottom bracket to rear wheel alignment, in order to clear the tire width. I also wanted to make this work with gears, as I knew the large tire would weigh a lot.
Originally I wanted to spoke up a fat tire rim with a standard bicycle hub, but this proved impossible due the the small rim size with the large tire.
After seeing one of the most creative bike ever (see Ode to the Chupacabra on
I got the idea of using a standard geared rear hub as a jack shaft or transfer hub between the front (bottom bracket) alignment and the rear tire alignment. This also solved the problem of gearing the bike, since I didn't have to mount the gears on the wheel itself. Thanks to The Atomic Zombie for instruction on one of his bike for the widened hub concept and for much other inspiration.
It weighs a lot, but it is a blast to ride and you never saw a bike get so much attention.
It took me a few months of noodling this around in my head and on paper before I started in earnest to create the "Fat Bastard" extreme fat tire sand bike. Hope you enjoy it as much as I do.
Let me also just say, for the record:
I did not set out to make the most efficient, or lightweight, or highest performance bike I could. It was all about maximizing tire size and working out the drivetrain issue. This was for fun! And also to learn how to weld and to see where this project might lead.
IF YOU LIKE, PLEASE GIVE THIS INSTRUCTABLE A GOOD RATING. THANKS!!
Step 1: Getting started - what you will need
1. The ability to weld. I never welded before this, but wanted to learn. I bought a $99 120V stick welder from Sears and taught myself on this project. It was painful, since the stick welding was pretty dirty so I had to do a lot of chipping (away the slag) and grinding and rewelding. Eventually, body putty covered all the rough (but strong enough) welds.
2. Some steel donor bikes and rigid electrical conduit. I cut up quite a few bikes to get the parts I needed. What parts you use and exactly how you configure the overall frame design are not critical. What is critical is placement and alignment of critical components. I
3. Wheels - I ended up using rear wheels from a Yamaha Blaster atv, because that is what I could find on Craigslist locally. It turns out they were a good choice because of the 4 bolt pattern which I will explain in later steps. Also, you can finda decent selection of used ones on ebay or other places online with tire sizes up to 11x22 (yeah baby!). I started with the wheels and designed the bike out around those. You need to know how wide to make the frame. I actually started with giant blue knobby tires and ended with rounder black knobbies (the first ones were a bit too square and messed with the handling)
4. A bunch of purchased (motorized) go-kart components from BMI Karts. More about those later. And some purchased bike components.
5. Basic knowledge of bicycles and power tools. I bought a 4" angle grinder and used a ton of cut-off wheels, flap wheels and grinding stone to cut and shape almost every component on the bike in some manner. This was a critical piece of equipment. I used my welding gloves and a face shield. I used flap wheels to remove galvanizing from conduits prior to welding. Do not weld galvanized steel. Also used conduit benders for curved framing members.
6. A big piece of cardboard for layout
7. Patience and some creativity