TUESDAY TECH TALK: WHEN DOES STACK & REACH CHANGE?

Q: I read a recent bike review, and it said that the stack and reach changed on the frame. How is that possible, and in what circumstances would that apply?

A: There are a few ways people measure stack and reach, and of the two, it’s the reach measurement that seems to confuse people the most. There is frame-reach measurement used by most companies and is not reliant on the bar and stem. Then there is a bike’s fit reach, which is normally the measurement that extends past the center of the head tube to the shifter hoods and helps a consumer choose the correct bar and stem combination for their specific fit needs.

Reach and stack are related because they rely on each other and are an invisible point where they meet. For reach, imagine there is a vertical line straight up from the bottom bracket; reach measures from that point to
the center of the head tube on a horizontal plane.

Stack measures the vertical distance from the center of the bottom bracket to the horizontal intersection for the top of the head tube. In short, if the frame’s horizontal level changes because of axle placement, then the relationship between where the vertical and horizontal lines meet changes slightly.

That being said, there are a few circumstances when the frame reach does technically change, but it is not that common. The most common circumstance is when a bike uses a flip chip to move the axle of the bike vertically. This doesn’t have to be straight up and down, but even a slight modification changes the frame’s relation to the ground, thus altering the stack and reach ever so slightly. 

The other circumstance would be if you ran a mullet wheel setup (mismatched wheel or tire sizes front to rear) and the outer circumference of the tires was not the same. This is fairly rare and something a consumer would do, not normally something that a manufacturer would sell. 

At the end of the day, these slight changes will have very little effect on how the bike actually fits and more on how the bike handles. For anyone with a flip chip on the vertical axis, I would say your fit should not be altered or changed when you swap positions.