Stack and reach explained: compare frames and transfer your position

Frame sizes like 56 or M say little about how you sit on a bike. Stack and reach do. Here you learn what the two values mean, how to compare two frames and how much spacers, stem length and stem angle change at the handlebar.

Transfer your position to a new frame: open the bike fit calculator →

What stack and reach mean

Both values describe where the top of the head tube sits, measured from the bottom bracket. Stack is the vertical height, reach the horizontal distance forward. Since the bottom bracket is also the reference for your feet, stack and reach tell you directly how high and how far forward you can mount the handlebar.

Frame sizes, on the other hand, usually measure the seat tube or are just letters, and every brand measures differently. Two size 56 frames can differ by several centimeters in stack.

What cockpit changes do

Movement of the handlebar center in mm. Starting point: 73° head angle, 20 mm spacers, 100 mm stem at -6°. Forward means further from the saddle.

Change	forward	up
10 mm more spacers	−3 mm	+10 mm
Stem 10 mm longer	+10 mm	+2 mm
Stem 0° instead of −6°	−3 mm	+10 mm
Stem +6° instead of −6°	−6 mm	+20 mm
Stem −17° instead of −6°	+2 mm	−19 mm
Frame with 10 mm more stack	0 mm	+10 mm
Frame with 10 mm more reach	+10 mm	0 mm

Comparing two frames

Compare stack and reach of your current frame with the new one. If the new frame has 10 mm less stack, you need roughly 10 mm more spacers or a steeper stem to get the bar to the same height. If it has 10 mm more reach, a 10 mm shorter stem roughly compensates.

Roughly, because the steerer is tilted. Spacers do not just raise the bar, they also pull it back a little. A steeper stem does the same. The table above shows how much. The bike fit calculator works through all combinations and finds the best one.

Limits when adjusting

How many spacers you can run depends on steerer length, and for carbon forks manufacturers often set a maximum. Very long or very short stems change the handling. If the cockpit needs big changes, a different frame size often fits better. The calculator points that out.

And the saddle?

Saddle position depends on the seat angle. A steeper seat angle puts the saddle further forward at the same saddle height. You compensate with the saddle position on the rails or a seatpost with different setback. Because that also changes the reach to the bar, the bike fit calculator always works out saddle and bar together.