You see stem angles of 17, 73, 6, 84? What gives? They refer either to the angle of the stem or 90 degrees less the angle of the stem (17 and 73 are the same). What is very confusing is how they affect the angle once they are mounted to a fork because the fork is also at an angle (the headtube angle).

Here’s how to calculate the angle of the stem in relation to the ground.

Take the fork (actually headtube) angle and subtract it from 90. That gives you the angle in relation to a line perpendicular to the ground. A 73 degree fork would result in an angle of 17 degrees.

Take the stem angle and subtract it from 90. A 73 degree stem would be 17 degrees. The gives you the number of degrees it will be off from a line perpendicular to the fork.

Next take the stem angle and add it to or subtract it from the fork angle (assuming a flip flop stem) so a 73/17 stem would either be 34 degrees upright or flat with a 73 degree fork (17+17=34, 17-17=0).

For an 84/6 the numbers are this 17 (fork) + 6 = 23, 17-6 = 11 so it is either 23 or 11 degrees up.

Thanks for reading – John Neugent

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