Check Your Bike Position and Fit

No — pose detection happens right in your browser. Only the resulting body-position numbers get sent to our server; your photo or video itself never leaves your device.

No. There are no accounts and no database — nothing about you or your measurements is saved on our side. Your browser keeps your last result and the measurements behind it only until you close it.

The LeMond/Hinault formula (inseam × 0.883) plus a small discipline offset (from −6 mm for cyclocross to +8 mm for TT/triathlon). It assumes a reference 170 mm crank; if you enter your crank length, the result is corrected 1:1 by (170 − crank length) — e.g. a 165 mm crank raises the saddle by 5 mm, a 175 mm crank lowers it by 5 mm. Kids' bikes are the exception: a more conservative version of the formula with no crank correction, and a parent should confirm the child can touch the ground with their tiptoes while seated.

From two bike-fit sources that give ranges for different ways of measuring the knee, so we use the one that matches how you capture your position. For a single photo, where you sit still with the pedal at the bottom, we use 25°–35° of knee bend (as widely cited from Holmes et al., 1994). For a video or several photos taken while pedaling, we use 30°–40° (Ferrer-Roca et al., 2012), a range measured on video during pedaling. Each range only applies to the kind of measurement it came from, so we never mix them. On screen they are shown as the angle between thigh and shin: 145°–155° and 140°–150°.

Each discipline has a typical torso-angle range based on general bike-fit convention. If you pick a riding position level and flexibility, we narrow that into a band personalized for you — this part is our own engineering judgment, not sourced from an external reference.

From the static fit norms Dan Empfield published on Slowtwitch. Road: handlebar drop is 11% of saddle height (an average measured on professional riders), and saddle nose to hoods is 0.72 × height − 0.78 × saddle height, ±25 mm. TT/triathlon: a 79.5° seat angle, saddle nose to the end of the extensions of 0.72 × height − 0.67 × saddle height, saddle nose to armrests of 0.58 of that, and an armrest drop from a published equation of saddle height and seat angle (±15 mm). The author calls these numbers checks for a position, not rules for setting it — treat them as a starting point.

It's a starting point, not a replacement for a professional bike fit — always double-check and fine-tune on the actual bike.

Only Height, Inseam, and Discipline are required — everything else is optional and just improves accuracy.