Stack and reach are the two numbers that actually decide how a bike fits you. Stack is how high the front of the frame sits; reach is how far forward it puts you. Get these two right and the bike suits your body; get them wrong and no amount of stem or spacer fiddling fully rescues it. You work directly with me, Lloyd Thomas.
What stack and reach mean
Measured from the bottom bracket, stack is the vertical rise to the top of the head tube and reach is the horizontal distance to it. Because both ignore seat tube length, they describe the frame’s real shape — how tall and how long it is where your hands and body go — in a way that transfers across brands.
That is why they matter more than a size label. A “56” from one brand and a “54” from another can fit the same rider if their stack and reach line up, and two frames with the same size sticker can fit completely differently.
Why they beat frame size for fitting
- A size label is a marketing shorthand, not a fit measurement
- Stack and reach are millimetre numbers you can compare directly
- They predict how high and how far the bars will sit before you buy
- The cockpit (stem, spacers, bars) then fine-tunes on top of a frame that is already close
How stack and reach translate to your position
The frame gives you a starting stack and reach; the cockpit adjusts the rest. Spacers and stem length shift effective bar height and reach within a range, but that range is limited — which is why the frame needs to be close first. When the frame is wrong, you end up with an ugly stack of spacers or an extreme stem just to reach a position the frame was never going to give you comfortably.
Where this fits your decision
If you are buying a bike, stack and reach are how you check it will fit before it arrives — that is what a sizing session produces. If you already own the bike and the position feels too long, too short or too low, a fit works within the cockpit range to get you as close as the frame allows.