Building a Better FXR Swingarm

Ex the flex

harley fxr swing arm fabrication

We are pulling the tubing in the bender to make the “Horseshoe,” which will add some lateral stiffness to the stock swingarm.

Words and Photos: Kirk Taylor

Although they haven’t made the Harley-Davidson FXR for quite some time, it is now as popular as it ever was with folks who want a great-handling bike for not a ton of money. There are even a few guys putting brand-new Twin Cam motors in them and superbike forks in search of the ultimate in handling, but one of the issues that has always plagued this model bike is rear-end flex.

One of the best things you can do for your rubber-mounted FXR is to prevent that lateral flex, or wiggle, they are known to have. An old trick that the flat-track racers would use is to build a U-shaped bend that could be welded up to the trailing arms on a swingarm. The racers found out that doing this greatly minimizes the lateral flex. For most racebike engineers it’s an understood principle that when you triangulate the framework it becomes stronger, and this principle was used a lot in both production bikes and racebikes a few decades ago.

With this principle in mind we decided to make up an FXR swingarm to mimic the old flat-track and roadrace swingarms and see how it worked. Follow along as we build a tracker-style swingarm for an FXR.

harley fxr swing arm fabrication

Then we tweaked the bends in the fixture a bit so everything was square.

Words and Photos: Kirk Taylor

harley fxr swing arm fabrication

Here is the finished “U” bend loop, which was perfect to our specs.

Words and Photos: Kirk Taylor

harley fxr swing arm fabrication

We test fit the loop and then made up some “bridge tube” braces with the same size tubing as our U-bend.

Words and Photos: Kirk Taylor

harley fxr swing arm fabrication

We chucked up the bridge tubes in our lathe and added a bit of coping (or chamfering) so they fit the space between the U-bend and the swingarm.

Words and Photos: Kirk Taylor

harley fxr swing arm fabrication

We made a few gussets where the U-bend met the stock material of the swingarm and welded it all up. (RM, Also use this image for the lead photo)

Words and Photos: Kirk Taylor

harley fxr swing arm fabrication

Here it is back from the powdercoater and ready to go! We found that this fab work actually stiffened up the ride very well.

Words and Photos: Kirk Taylor