Product
GPS + BT Reset
A distance-logging tool for rally reconnaissance. Integrates precise GPS measurement with a Bluetooth steering-wheel button for hands-free resets.
Side build · Rally app
RallyRec
A professional rally reconnaissance app combining GPS tracking and a Bluetooth steering-wheel button. Built for co-drivers to log precise distances without taking their eyes off the road.
iOS
development
2019
– Present
Overview
Hardware and software for the cockpit
Team & context
Co-designed with pros
A side project built primarily in 2019, designed closely with Olivier Brouze, a professional French rally co-driver. Stable since 2022 and still actively used today.
My Role
iOS Engineering
Implemented the iOS app from functional specs, integrated Apple's location APIs for tracking, and wired the Flic Bluetooth button SDK.
The opportunity
Bringing precise metrics to a harsh environment
The friction
Outdated or clunky tools
Good pacenotes rely on precise distances. Crews used tripmasters or manual apps, but needed an accurate, repeatable solution that didn't add complexity inside the car.
The challenge
Meter-level accuracy in motion
GPS had to hold up over multiple passes through tunnels and varied speeds. The reset interaction had to work reliably every time, without distracting the co-driver.
How it works
A frictionless loop for reconnaissance
Drive, reset between corners, and keep distances flawlessly aligned with your pacenotes.
Start
Track the stage
Start tracking before reconnaissance. The app tracks GPS distance and displays total and partial distances in large, readable digits.
Reset
Hardware integration
A Flic Bluetooth button on the steering wheel lets the co-driver reset the partial distance with a simple thumb press, no screen tapping.
Log
Write the notes
The co-driver glances at RallyRec for precise corner distances. Consistent measurements reduce guesswork and mental load during recce.
Execution
Focusing on reliability over features
Product scope
Do one job perfectly
Ignored requests for maps or live timing. Kept RallyRec strictly about distance for reconnaissance, building a simple mental model for pilots.
Field testing
Tune GPS in the real world
Validated Apple's location APIs by driving loops in a car park to check how distances behaved at different speeds and passes. Tuned for asphalt, not simulators.
Hardware integration
Flawless Bluetooth experience
Wired the Flic SDK to the reset logic, handling reconnections, debouncing, and ignoring double presses. It feels like a physical extension of the app.
UI Design
Respect the cockpit context
Translated visual specs into an interface built for one-second glances: massive numbers, high contrast, and flat interactions. Built like an instrument, not a mobile app.
Result
Trusted by rally crews across the board
800
Paid users
800 paid downloads with no free trial. Every purchase is a genuine commitment from a rally professional who needs reliable distance tracking.
8,000+
Rallies covered
Each user logs an average of 10 rallies. That's thousands of reconnaissance runs measured and validated with RallyRec in real conditions.
~120K km
Measured with RallyRec
With an estimated average of 15 km per rally stage, that's roughly 120,000 kilometres of reconnaissance tracked and measured through the app.
Since 2022
Stable & maintained
The app reached a stable, self-sustaining state in 2022. Minimal upkeep, mostly adapting to new Flic button iterations.
Retrospective
What I learned
GPS accuracy is a product decision, not just a tech one
The trade-off wasn't about raw precision. It was about consistency: the same stretch had to show the same distance every pass. Tuning for perceived reliability mattered more than chasing centimetre accuracy.
The best UI is the one you forget
In a rally cockpit, if the copilot looks at the screen for more than a second, something is wrong. Massive numbers, zero taps, extreme contrast. It's the opposite of standard mobile design.
Working with one domain expert beats surveying 100 users
A few deep-dive calls with Olivier taught more than any online feedback could. When the domain is this specialised, one deeply engaged expert gives sharper product direction than a broad panel.
Saying no to features is the feature
Users asked for maps, live timing, session logs. Refusing everything kept the app usable under rally conditions. When stakes are real, doing one job flawlessly beats doing ten averagely.