The stack-to-reach ratio (STR) is the stack divided by the reach: a unitless number that sums up whether a bike is relaxed or aggressive. Lower = more stretched out and aggressive; higher = more upright and comfortable. It serves to compare two bikes at a glance — but it misleads across sizes and brands, so it doesn't replace looking at the absolute stack and reach.
It's the quickest way to read a bike's "posture" in a single number. Useful, but with traps worth knowing before you trust it.
It's a simple division:
For example, a bike with 620 mm of stack and 470 mm of reach has an STR of 620 ÷ 470 = 1.32. Because it's a quotient, it carries no units: it just compares the height with the length.
A high STR signals a bike designed to ride more upright and comfortable (long rides, mellow trail); a low one, a more crouched and aggressive bike (XC racing, aero road). It's a good first filter when comparing two models: if one is 1.30 and another 1.45, you already know they'll seat you very differently even if the size says the same.
The STR has three important blind spots: (1) it doesn't scale well across sizes — the STR usually drops on large sizes because the reach grows faster than the stack, so comparing an M with an XL by their STR misleads; (2) it ignores the components (stem, spacers, handlebar angle) that change your real posture; (3) it's static: it says nothing about how the position changes under load (see dynamic geometry). That's why it's a summary, not a verdict.
Stack divided by reach. A number that sums up whether the bike is upright (high) or aggressive (low).
In MTB, ~1.3 or less tends to be aggressive; ~1.4–1.5 more upright. References, not laws.
Only between bikes of the same size and type. Across different sizes or brands, use absolute stack and reach.
Tell us the model or your stack and reach and we'll tell you its STR, what it means and whether it fits your body and style. Message us on WhatsApp
© 2026 BikeLab Studio. Content under CC BY 4.0: you may copy, translate and publish it, even for commercial purposes. Citation is mandatory. Without attribution, the license terminates automatically (CC BY 4.0, §6.a) and the use becomes copyright infringement: we request the removal of the content and its deindexing. · Design and ownership: Carlos Ravello Joo