# Fox + Son Jetmax — Rotax jetting calculator

> Rotax engine jetting and tuning calculator with gear chart. (iPhone/iPad app by Trophy Inc..)

- Source: https://appshunter.io/ios/app/fox-plus-son-jetmax/id6748326003 (this page in markdown: same URL + `.md`)
- Developer: [Trophy Inc.](https://appshunter.io/developer/1752591571)
- Category: Sports, Utilities
- Price: Free with in-app purchases
- Rating: 5.00/5 from 2 App Store ratings · 1 written reviews indexed
- Age rating: 4+
- Requires: iOS 15.1 · 16 MB
- Languages: English
- Released: 2025-09-29
- Data updated: 2026-07-04
- Monetization: subscription
- User reviews in markdown: https://appshunter.io/ios/app/fox-plus-son-jetmax/id6748326003/reviews.md

## What is Fox + Son Jetmax?

Precision jetting made easy — This app helps you calculate jetting for Rotax engines based on weather and altitude.

Now every Rotax racer has access to the same jetting Fox + Son has used to power our engines to countless Rotax National wins and Grand Finals tickets. After many months of development and testing, we have successfully brought the same jetting algorithms we use on our dyno to a quick, easy-to-use app. We have also included all of our popular Rotax tuning tips that are found on our website, along with a handy interactive gear chart for your convenience. As we do with our website, we will continually update the app as we discover new tuning information. Anytime a new cylinder or part is introduced, all of the testing we do at the shop will flow directly to Jetmax.

Jetmax will also calculate the relative horsepower for that atmospheric condition. The relative horsepower percentage is helpful information to have when selecting your gear ratio. In certain situations you can benefit from increasing your gear ratio when HP is low & decreasing your gear ratio when HP is high.

Whether you're competing at the track or fine-tuning your kart for practice, Jetmax gives you accurate, reliable recommendations so you can focus on performance.

Features:
- Jetting calculator for Rotax engines
- Calculates relative horsepower
- Includes an interactive gearing chart

Engineered by racers, for racers — Fox + Son Jetmax App delivers the tools you need to stay competitive on race day.

*You must have a valid subscription in order to use this app.

## Key features

- Rotax engine jetting calculator
- Weather and altitude adjustments
- Relative horsepower calculation
- Interactive gear chart
- Rotax tuning tips

## Pricing and in-app purchases

Base price: Free.

**Subscriptions**

| Subscription | Price | Period |
| --- | --- | --- |
| Premium Yearly | $7.99 | per year |


## Recent user reviews (1 of 1)

All indexed reviews: https://appshunter.io/ios/app/fox-plus-son-jetmax/id6748326003/reviews.md

### 5/5 — It’s a must

*2025-10-20*

It is the new must have if you have a Rotax at the track

## Frequently asked questions about Fox + Son Jetmax

### What is Fox + Son Jetmax?

Fox + Son Jetmax is a mobile application designed to calculate precise jetting for Rotax engines. It uses weather and altitude data to provide optimal tuning recommendations for racers.

### How does Fox + Son Jetmax help with performance?

Jetmax calculates relative horsepower, which is crucial for selecting the correct gear ratio. It also provides accurate jetting recommendations to ensure your engine runs at its best.

### Is Fox + Son Jetmax free to use?

No, Fox + Son Jetmax requires a valid subscription to use. The Premium Yearly plan is available for $7.99 per year and includes a 7-day free trial.

### What devices does Fox + Son Jetmax support?

Fox + Son Jetmax is currently supported on iPhone and iPod devices.

### How often is Fox + Son Jetmax updated?

The app is updated regularly to incorporate new tuning information and testing results from new cylinders or parts. The latest version is 1.0.3, last updated on April 2, 2026.

### Does Fox + Son Jetmax have ads?

No, Fox + Son Jetmax is ad-free. The application is designed to provide an uninterrupted user experience for racers.

### What is the age rating for Fox + Son Jetmax?

Fox + Son Jetmax has an age rating of 4+, making it suitable for a wide range of users.

### Can I cancel my Fox + Son Jetmax subscription?

Yes, users can typically cancel their subscription through their device's app store settings. The app offers a 7-day free trial for the Premium Yearly plan, allowing users to test it before committing.

## Version history (last 3 releases)

### 1.0.3 — 2026-04-02

-Added "US Spec Micro" engine type
-Optimized jetting for longer tracks

### 1.0.2 — 2025-10-01

Improved bug report

### 1.0.1 — 2025-09-29

No release notes.

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*Data collected daily from the US App Store and indexed by [AppsHunter](https://appshunter.io/). User reviews are verbatim App Store reviews. Ratings, prices and chart positions refresh continuously; this snapshot is from 2026-07-04.*