4-wheel friction circle and Tire vector visualizer

[hirotaka_k]

Hi everyone,
I'm an FK8 owner and I’ve been developing a smartphone app that calculates and displays individual friction circles (G‑G diagrams) and G‑vectors for all four wheels, instead of a single combined one.

This screenshot shows the moment when the vehicle goes from a left turn to a right turn in an S-curve. The vehicle's weight is shifted to the left, and the friction circle appears to be larger on the left side.

Since the early FK8 system — and most apps — do not show friction circles, I decided to build the tool I always wanted.
Video demo:

(Additional behavior demo is uploaded on the same channel)
I'm now running a closed test on Google Play and I'm looking for testers, especially FL5 and FK8 Type R owners.
Street or track — any data is helpful.
What I’d appreciate feedback on:
-Do the friction circles and G‑vectors behave correctly?
-Is the UI readable while driving or reviewing logs?



The app will be completely free. Once enough testers join and Google’s review is finished, I will release it publicly. My goal is to help drivers use more of their tire’s potential and hopefully contribute to faster lap times for everyone.


About data:
The app does not upload any personal information. Sensor data stays on the device and is used only for real‑time calculation.
If you'd like to join the test, please reply or DM me.
Also, I am Japanese and using translation tools, so please forgive any strange wording. Thank you!

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[hirotaka_k]

Thanks!! not need now.(2026/03/19)

Update for anyone interested in joining the closed beta:

Google Play has introduced new requirements for individual developers before an app can be released publicly.
To move forward to the final release, I need to reach:

• 20 testers
• 14 days of continuous participation by those testers

Once this requirement is fulfilled and Google’s review is completed, I will release the app publicly and free of charge.

If you are willing to support the project, here is how to join the closed beta:

1. Join the Google Group (used for tester management):
[https://groups.google.com/g/friction-circle-app-beta-testers]

2. After joining, please wait 10–20 seconds and then open the Google Play test link:
[https://play.google.com/store/apps/details?id=io.github.kajimae.frictioncircle]

3. Install the beta version from Google Play.

The app does not upload any personal data, and sharing logs is optional.
Even a short 5–10 minute street drive provides extremely valuable data.

Thank you very much to anyone who joins — your support directly helps the app reach public release.

 

[hirotaka_k]

Just a quick note to say thank you.
I’ve received some helpful input and the project is moving forward as planned.
Really appreciate everyone’s cooperation.

Fixed an issue where FWD cars showed rear tires contributing to acceleration.Now acceleration force is distributed based on drive-train (front/rear/adjustable), not just load transfer.

 

[hirotaka_k]

Small update for those who were following this.

The closed test wrapped up on the today, and the app is currently going through store review.
Nothing special to announce yet — just sharing progress.

My goal is still the same:
if visualizing the friction circle helps with understanding vehicle behavior, that’s all I’m aiming for.

 

[hirotaka_k]

Thanks!! not need now.(2026/03/19)

Google requires me to run an additional 14-day closed test for my app.
Please help. I need 3 more testers to join.

 

[Sorabaxton]

How does the app connect to the vehicle and receive information?

 

[Mrjustin81]

This sounds really interesting. I have iPhone, otherwise I would offer to test it.

How does the app connect to the vehicle and receive information?

And also this

 

[marcusm86]

Would it be helpful if i install this on a phone and then connect it back to the internet later? I do not have an android with cellular connection.

 

[hirotaka_k]

How does the app connect to the vehicle and receive information?

Thanks message.
It does not connect to the vehicle in any way.
The app uses only the smartphone’s built-in sensors and does not communicate with the vehicle.

I infer vehicle behavior from the phone’s accelerometer data using filtering and condition-based logic, with the gyroscope used to confirm certain states.
I avoid relying on OBD vehicle data because its latency and slow update rate often mean that what you see on-screen lags behind what you feel in real time.

 

[hirotaka_k]

Would it be helpful if i install this on a phone and then connect it back to the internet later? I do not have an android with cellular connection.

No Plobrem.
After install, the app does not use a cellular connection or Wi‑Fi.
It works completely offline and uses only the phone’s built‑in sensors.

 

[hirotaka_k]

This sounds really interesting. I have iPhone, otherwise I would offer to test it.
And also this

Thanks! Sorry though — I don’t have a Mac, so I can’t build an iOS version right now.
I’ll put it on my Christmas wish list

 

[marcusm86]

No Plobrem.
After install, the app does not use a cellular connection or Wi‑Fi.
It works completely offline and uses only the phone’s built‑in sensors.

Sounds good. Ill try to remember to bring this other device with me next time i drive to get you some data. I changed the weight, tread, wheelbase and everything in there to the proper numbers. I am not sure what you are wanting for "accel traction split". Also are you wanting something to be put in for the tire & grip saturation area?

 

[hirotaka_k]

Sounds good. Ill try to remember to bring this other device with me next time i drive to get you some data. I changed the weight, tread, wheelbase and everything in there to the proper numbers. I am not sure what you are wanting for "accel traction split". Also are you wanting something to be put in for the tire & grip saturation area?

Thanks for trying t app and feedback!

Accel traction split
From the measured acceleration, the app cannot determine whether the driving force is from the front, rear, or all wheels.
This setting lets you specify that.
Far left = FWD mode.

Tire μ
A typical value is around 1.0–1.3.
Grip saturation
This is roughly the G level where the tires start to slip (for example during braking).
Try around 1.0 g.

Drop rate
After the tire starts to slide, try about a 30% drop in grip.



These are just starting values, so feel free to adjust and see what matches your car best.

 

[hirotaka_k]

Quick update and big thank you for all.

The app has passed Google Play review and is publicly available:
https://play.google.com/store/apps/details?id=io.github.kajimae.frictioncircle
Not about data handling has changed.

I really appreciate everyone who helped with testing and feedback.
If you end up trying it and notice anything odd (or useful), feel free to comment or DM me.

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