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.