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Bicycle Frame Geometry: Wheel Flop

Staying on the subject of steering and the general front end of the bike, it’s time to address wheel flop. Wheel flop shares similarities to trail, as it is set by fork rake and head tube angle. How it differs however is that it relates to how the front axle position changes as a rider turns the handlebars. What occurs nearly ever instance is that the axle height lowers as the handlebars are turned. This phenomenon is more prominent on a slacker head tube as well as forks with less rake.

What this means in plain language is that wheel flop allows a bike to turn with less effort at low speed. A bike with more flop will make a sharp turn far easier at slow speed than one with less flop. Optimal wheel flop is therefore a balance. While it enhances maneuverability, too much means a bike that is difficult to keep in a straight lline.

Opposing forces

When it comes to application, wheel flop effectively neutralizes trail. With that said, the two are interlinked. Increase one, and the other increases to suit. Bicycle design must contain both of these and it is impossible to construct a bike with little trail and high wheel flop. The inverse also holds true.

Where wheel flop can be used to recognize the steering behavior of a range of head tube angle and fork rake combinations that may share the same amount of trail. Various combinations may yield the same trail, but the amount of flop can differ. This is where wheel flop is useful in determining the difference in steering response. 

An example

A bike with a slack head tube and higher rake may have the same trail as a bike with a steep head tube and lower rake. The wheel flop of each bike will be different, however. The bike with a slacker head tube will yield a higher wheel flop, offering more nimble steering at lower speed. The more aggressive bike with less rake will have a lower wheel flop. This will aid in high speed stability at the cost of low speed maneuverability.

Wheel flop may be a bit further down the rabbit hole of bike geometry than most people are willing to go. I think it’s a fascinating aspect of how a bike behaves while ridden. I think those of us who know exactly how we want a bike to ride will find it important. This is especially important when it comes to a specific kind of bike and it’s application. We’ve all ridden bike that feel perfect, and others that just didn’t work properly for our riding style or the terrain. Wheel flop is just another one of those contributing factors. Stay safe out there, and as always, keep the rubber side down!