This Instructable explains how I modified my single wheel bicycle trailer to work with my Fat Bike.

See original trailer build here: https://www.instructables.com/id/Single-wheel-bicyc...

The rear axle is wider on my Fat Bike than on my other mountain bikes. In addition, the diameter of the wheel/tire is greater than on a standard 26" mountain bike.

The solution was to create dropout extenders (mounting plates with spacers) which increased the width of the trailer mount dropouts as wheel as increased the length of the dropout arms/legs. The dropouts insert onto sleeves built onto the quick release axles.

This would allow relatively easy conversion back and forth between my Fat Bike and my other bikes.

Step 1: Parts and Tools

The project required the following parts:

(1) Bob trailer quick release axle (available here):

https://www.biketrailershop.com/bob-trailer-parts-...

(1) quick release axle for sacrifice (cutting up)
(2) aluminum plates. Thickness to match Bob trailer quick release axle sleeves, or slightly thicker, which then requires some grinding to suit
Spacers and bolts

I used the following tools:

Jigsaw with metal cutting blade
Drill/drill press
File
Wrenches

Step 2: Fabricating Trailer Axle and New Drop Out Extenders

Measure Fat Bike quick release axle length. Cut Bob trailer quick release axle in half. Cut piece out of sacrificed quick release axle to length required to match existing fat bike axle. Weld, or have professionally welded, the two Bob trailer axle halves with the piece of axle between to make a new longer Bob trailer axle.

Draw out the profile of the aluminum plate as required to suit the added length needed to clear the tire.

Drill a hole to match the diameter of the axle sleeve onto which the dropout will fit.

Cut the aluminum plate to create a slot up to the above noted dropout hole.

Drill a hole in the trailer dropout plate, just ahead of the existing dropout mounting slot. This provides two bolt holes for mounting the trailer dropout to the new dropout extender plates.

Drill two holes in the new dropout extender plate to align with 1) the existing trailer dropout slot and 2) the new hole in the trailer dropout plate.

Drill small hole through front end of extender plate for inserting a retainer pin to secure dropout on axle sleeve. See original Instructable for information on retainer pin installation and fabrication.

Drill hole through plate for small machine screw to be used for securing the retaining pin.

Bolt extender plates onto trailer dropouts with plastic spacers (Lowes/Home Depot) as required to suit width of modified (widened) trailer axle.