The aesthetics of a bike are very important. A lot of customizers try to envision what a motorcycle with proper proportions would look like in their mind. Many stock motorcycles may have features that are for function, but hurt the proportions of a motorcycle. A huge example is fender height from the tire. In most stock motorcycles, the tire must move up and down within the fender to allow for suspension. This means the fender is mounted far from the tire. A motorcycle, like a chopper with no suspension, can mount the fender as close to the tire as possible. The tire cannot rub the fender because this will cause a very dangerous scenario for the rider.
Mounting a fender is something a do-it-yourself can handle as long the person has basic metal fabrication and welding skills. It is important that it is done correctly, especially if a passenger is going to be sitting on it. Weld must penetrate and materials should be the right thickness and strength.
Removing the old fender is the first step if there is one. Existing fenders are mounted with bolts to a strut or frame tube. Wiring should be removed carefully. The old fender may contain clips for taillights and turn signals (these need to be put back on). The same fender can be rigid mounted to the swing arm but it will probably not fit right.
A fender generally has a radius designed for suspension travel. If the same stock fender is mounted closer to the tire, the radius may be different than that of the wheel. However, the fender can be re-radiused with relief cuts. This is done by cutting wedge shapes of metal out of the edge of the fender. The fender can then be reworked to form a tighter radius. Keep a spacer between the tire and fender using rubber tube or an old motorcycle chain taped to the top of the tire. An aftermarket fender can also be used. When mounting to a swing arm it is important the fender have a front and back mount (even one in the middle would be ideal). The front mount which is closer to the swing arm pivot can be mounted directly to the wing arm using a bung. A nut can be welded to the fender and a sleeve be welded to the swing arm. The rear mount can be made using a strut or sissy bar. If the axle plate has room, it can be drilled and tapped to receive a bolt. Using a bolt and sleeve, a piece of flat or round stock can then be welded to the sleeve. When making a strut, the solid round or flat stock would be cut at the desired height of the fender. A bung or nut can then be welded to the fender and another sleeve welded to the newly made strut. A bolt will go through the sleeve and thread into the bung. A single seat must be used in the application because the fender will be moving up and down with the suspension. A pillion pad can be mounted to the fender for a passenger to sit. This setup may be uncomfortable for the passenger, especially going over rough terrain.
A chopper built from scratch will be more like a blank canvas. Fender options are limitless. An old trick back in the day was to use a trailer fender or a spare tire cover. Today’s aftermarket allows anyone to find anything they want. The options go from chrome, aluminum, peaked to flat to flared, etc. Once the fender is selected, it is mounted just as a fender on a swing arm styled motorcycle. Without any moving suspension, mounting a fender is quite easy. Use a spacer like a rubber hose or motorcycle chain between the tire and fender. This allows for the tire to expand under riding conditions and not rub the fender. The fender should be mounted in at least two places, but three would be ideal. The front mount can be made with bungs and sleeves welded to the frame tube and fender. The rear mount would be made with a strut or sissy bar. A custom made sissy bar can have flat stock welded to it and fit underneath the fender. Holes can be drilled through the fender and bolts thread into the flat stock. This gives a very concealed and nice looking mount. These can be hidden under the seat. Depending how close the fender is to the chain it may have to be notched to clear it. A pillion pad or 2 up seat can be mounted to the fender.
Once fabrication is done the fender can be dismounted. Some body work may be needed and final paint can be applied. Bare metals on struts and mounts can be plated or painted. All the parts will then be reassembled for the final product. Re-run wires for turn signals and stop lamps. With a little imagination and skill a rigid mounted fender can be executed perfectly.