Frame and fork
In order to fit 4-inch wide tires, fat-bike forks need to be significantly wider than a standard mountain bike fork. Many fat-bike front forks are built to accommodate a 135-mm front hub, wider than the standard 100-mm front hub.
Some fat bike enthusiasts will put a gear on their front wheel so if something happens to their rear hub, they can swap the front and rear wheel and keep riding.
The rear triangle also has to accommodate the 4-inch wide tire. To do this, the chainstays and seatstays are bowed out and lengthened to the point that some fat bike riders will but a 29-er wheel on a fat bike frame and ride a normal tire in the summer.
When sporting 4-inch tires, a standard bottom bracket won’t allow the chain to clear the tire through a full range of gears, thus most fat bikes have a 100-mm bottom bracket shell and bottom bracket spindles ranging 145-mm to 171-mm.
The geometries of fat bikes are similar to standard mountain bikes in terms of head tube and seat tube angles.
Generally, snow bikers prefer to be more upright than their dirt riding counter parts. Having less weight on hands is a key component to keeping blood circulating in the fingers and keeping hands warm in cold conditions and since snow bikes tend to move at slower speeds, aerodynamics play a less important roll in efficient forward movement.