Free AI Bike Fit for Indoor Trainers — Analyze Your Cycling Position at Home
What is bike fitting?
Bike fitting is the process of adjusting your bicycle's geometry — saddle height, handlebar reach, and riding position — to match your body's proportions and riding goals. A proper bike fit reduces injury risk, improves power transfer, and increases comfort on long rides. Research shows approximately 80% of cyclists ride with at least one measurement outside the optimal range, often contributing to knee pain, back discomfort, or reduced efficiency — especially on smart trainers where static position compounds small misalignments.
I ride on my smart trainer and wanted to verify my position was actually optimized for indoor cycling. So I built AxyZ. You record a short video on your Zwift, TrainerRoad, or smart trainer setup, upload it, and it measures your saddle height, hip angle, torso lean, and pedaling stability against the same targets professional fitters use. Then it tells you what to fix first.
It will give you a science-backed read on where you are today — and that's worth a lot when you're trying to figure out why your knee started aching after you put on a new saddle.
Read the story →Why Bike Fit Matters (And Why It's Hard to Get Right)
Bike fit is the #1 cause of cycling knee pain. A saddle positioned just 1cm too low or too high creates biomechanical stress that accumulates over weeks of riding—anterior knee pain, IT band pain, or lower back strain.
Most cyclists respond by adjusting the saddle and hoping it helps, reading conflicting advice online, or paying for a professional fit ($150–$400, 2–3 hours, travel required). For many, that option isn't realistic. So they guess. And many keep guessing for months.
Here's the opportunity: The measurements that matter most—saddle height, hip angle, torso lean, pedaling stability—are measurable, standardized, and reliable. These four variables account for 80% of common fit problems. They can be measured from a phone video using the same computer vision technology used in professional sports analysis.
AxyZ does that in 2 minutes, free. It's not a replacement for a professional fit. It's the answer to the question you have at 11 PM when something doesn't feel right.
Free to try · No credit card required
Cycling Position Metrics AxyZ Measures
Saddle Height
Knee angle at bottom dead center
Target 35–40° of knee flexion at BDC. Too low over-flexes the knee (above 40°) causing anterior knee pain; too high under-flexes it (below 35°) causing hip rocking and IT band strain.
Check your saddle height →Hip Angle
Hip flexion at top dead center
Target minimum 60–69° at TDC. A hip angle below 60° indicates hip flexor compression from saddle height or reach; above 69° suggests an overly upright position for the discipline.
Torso Lean
Upper body angle relative to the bike
Scored against your bike type — road, gravel, mountain, or triathlon. Asymmetry and excessive hand-loading are flagged as secondary indicators.
Pedaling Stability
Hip drop variance across a full pedal cycle
A saddle set too high forces the hip to dip on each downstroke to reach the pedal. AxyZ measures this vertical hip variance across multiple pedal cycles — the most reliable side-view indicator of saddle height overshoot.
AxyZ covers the X axis (sagittal angles — knee, hip, torso) and Y axis (vertical hip stability). The Z axis — lateral knee tracking and cleat alignment — requires multi-camera 3D capture and is the domain of a professional fitter.
Bike Fit for Indoor Trainer Riders
Indoor trainer and smart trainer cycling puts unique demands on your fit. Unlike outdoor riding where natural bike movement compensates for small position errors, a stationary trainer magnifies saddle height mistakes. The same 35–40° knee flexion target applies, but trainer tilt affects your effective saddle height — even 1–2° of tilt can shift your position by 3–5mm.
Many Zwift and TrainerRoad riders set their saddle 3–5mm lower than their outdoor position to account for the absence of bike sway on a static trainer. AxyZ measures your actual knee angle and hip stability on your trainer setup, accounting for tilt and static position. Upload a video of yourself riding on your indoor setup, and we'll tell you exactly what to adjust.
How AI Bike Fitting Works
- 01Set your phone level with your pedals, 6–10 ft away. Film 10 seconds from the right side with your full body in frame.
- 02Enter your height, crank length, and bike type. AxyZ uses these to calibrate angle measurements to your specific geometry.
- 03The AI tracks every joint frame-by-frame across a full pedal cycle, scores each fit variable, and ranks the adjustments by impact.
How Accurate Is AI Bike Fitting?
AxyZ uses Google MediaPipe Pose, a computer vision model that tracks 33 anatomical landmarks at 10 frames per second. Across a 10-second video, it analyzes approximately 100 frames and averages measurements across multiple complete pedal cycles — reducing the effect of any single noisy frame.
For sagittal-plane variables — saddle height, hip angle, torso lean, and pedaling stability — a stable, level, side-on video reliably identifies whether your measurements are within target range and by how much they deviate. These are directional measurements: they tell you the right adjustment and its magnitude.
Lateral variables (cleat alignment, knee tracking, fore-aft saddle position) require a front or rear camera and 3D motion capture. AxyZ does not report on these — reporting on variables a single side-view camera cannot measure accurately would produce incorrect recommendations.
AI bike fit vs. professional bike fit — full comparison →Try first — no account needed
Free Saddle Height Check
Two photos and a playing card. We measure your inseam and current saddle height and tell you exactly how much to raise or lower it.
Check my saddle height →Last updated: · Built by a competitive Zwift racer and software engineer · Analysis engine: Google MediaPipe Pose · Methodology