I had knee pain for months cycling. So I built a free (AI) bike fitting tool

Elouan — Thu, 22 Jan 2026 14:30:57 +0000

Last year I started getting serious about cycling. Bought a decent road bike, started doing 50-60km rides on weekends. Life was good.
Then my knees started hurting.

At first I ignored it. "It'll pass", I told myself. It didn't. After 3 months of increasing pain, I finally looked into bike fitting.
The options were... not great:

Professional bike fitting: €150-300 for a 2-hour session. Cool, but I'm not made of money...

MyVeloFit: $75/year. Decent tool but felt expensive for what it is
YouTube tutorials: "Just measure your inseam and multiply by 0.883", yeah that doesn't work for everyone

Random online calculators: Input your height, get generic numbers that don't account for your actual body proportions

I'm a developer. You probably know whats coming.

The rabbit hole

I spent way too many evenings reading about bike biomechanics. Turns out the science is pretty well documented – knee angle at bottom of pedal stroke, hip angle, reach... there are established ranges that work for most people.

The hard part isn't the math. It's measuring yourself accurately while on the bike. That's why pro fitters use expensive motion capture systems.

But here's the thing: we all carry HD cameras in our pockets now. And pose detection AI has gotten scary good in the last few years.

So I thought – what if I could just... point my phone at myself on a bike trainer and have AI figure out my joint angles?

What I built

MyBikeFitting is basically that. You film yourself pedaling (or just upload a photo), the AI detects your body position, measures your joint angles, and tells you what to adjust.
The key things I wanted:

100% free. Not freemium, actually free
No account needed. No email, no signup, no BS
Privacy-first: the analysis runs in your browser. Your photos never leave your device
Works in French, Spanish and English (I'm French, seemed important)

It's not going to replace a professional fitting for competitive cyclists. But if you're a weekend warrior like me who just wants to stop hurting, it does the job.

The tech stuff (for those who care)

Next.js for the frontend
MediaPipe for pose detection
All processing happens client-side
Hosted on DigitalOcean

The pose detection accuracy is honestly impressive. I tested it against my own measurements and it's within 2-3 degrees most of the time. Good enough to tell if your saddle is way too low.

What actually happened
I fixed my knee pain. Turns out my saddle was about 2cm too low. Such a simple fix, and I suffered for months.

Why I'm posting this
Honestly? I'd love some feedback. The tool works well for me but I've only tested it on like 15 people.
If you cycle and have 5 minutes, I'd really appreciate if you tried it out and let me know:

Did the detection work on your setup?
Were the recommendations helpful?
Anything confusing in the UI?

Link: mybikefitting.com

No tracking, no analytics that spy on you. I literally can't see what you're doing on the site. So if something breaks, please tell me in the comments 😅

DEV Community: Elouan

I had knee pain for months cycling. So I built a free (AI) bike fitting tool