The most common questions I get through the Contact page are related to Lee McCormack’s RAD measurement. RAD stands for “rider area distance” and it represents the 2D projected distance between the bottom bracket and the middle of the grips. It has become a common bike sizing method for many riders on modern bikes.
The Bike Geometry Calculator on this site has been developed in a way to allow a number of methods to measure bike fit, including RAD. In fact, if your inputs are good, you can calculate RAD very accurately for bikes you might be considering but can’t get your hands on to measure yourself.
Enter the frame and cockpit measurements and the calculator will calculate RAD to the 1/100th of a millimeter. The cockpit fit measurements can be found by clicking on the “Include Cockpit Fit Measurements” at the bottom of the geometry table, which is on by default.
The key to calculating RAD correct on paper is to identify a few cockpit parameters, particularly in the handlebars. You’ll need to know the handlebar rise, upsweep, backsweep, length of the swept section (sometimes called the control area). You’ll also need to know the stem length, stem rise, stack height to the center of the stem clamp to the steerer tube and handlebar roll angle. If you don’t have access to all those parameters, you’ll get in the ballpark with some estimates, but the quality of the outputs are only as good as the quality of the inputs.
With all those parameters entered into the calculators, you’ll find RAD as a calculated output.
Also included in the calculated results is RAAD or RAD angle, which stands for “rider area angle in degrees” and represents the angle of the RAD line from horizontal as shown in the figure above.