A Japanese tuner transforms an Alfa Romeo 4C into a race car without modifying the engine: it beats its more powerful rivals

The TEZZO RT1 is a Japanese-made model based on Alfa Romeo 4C produced by TEZZO, a tuning company specializing in Alfa Romeo, Abarth, Fiat, and Alpine. Their cars regularly compete in the Alfa Romeo Challenge Japan championship.

What does RT1 mean?

RT1 stands for «Radial Tire No. 1.» The concept? To develop a car capable of being extremely fast on the track using street-legal tires, rather than slicks.  TEZZO emphasizes that these cars must remain enjoyable to drive on public roads. The slogan they use is literally:«A comfortable race car for the road.» 

Most of the work, therefore, focuses not on the mechanics but on dynamic behavior, with many parts developed specifically in Japan—a philosophy inspired by “Touge”-style road racing.  The Alfa Romeo 4C RT1 is not designed to increase power but rather to make the car more stable at high speeds and easier to handle. A well-balanced car is often faster than one that is simply more powerful.

“Being able to accelerate sooner without worrying”

This project began at the turn of 2015–2016. Originally, the car was not yet an RT1, but a 4C in the “luxury” trim. The goal was to enhance the production car without compromising its comfort. The first modifications included a “Quattro LXY-S» exhaust system, a carbon fiber intake, TEZZO threaded valve stems, and forged wheels.

The RT1 project was born in 2017 with the launch of the competition program. The engineers identified several issues with the original 4C: a very short wheelbase, a turbo that kicks in very abruptly, a transition from understeer to oversteer that can catch drivers off guard, and a lack of confidence at high speeds.

They then embarked on a massive project involving geometry, shock absorbers, springs, braking, electronic calibration, and tire selection—all of which remained street-legal. The goal: to make the car easier to drive at the limit.

Racing Success

Starting in 2018, the Tizzo RT1 began taking on its rivals in the Alfa Romeo Challenge Japan races. The car secured pole position across all categories—ahead of several GTAs—right from the championship opener, followed by an overall victory at Fuji. TEZZO explains that most of the advantage comes not from the engine but from the driver’s ability to stay at full throttle longer.

In 2019, the car’s exterior has changed very little. However, a great many details have been revised. We’ve revised the suspension settings, stiffness, and balance, as well as weight reduction and ECU calibration. This season is primarily focused on improving the car’s reliability. They explain that an amateur driver gains more lap time with a predictable car than with an extra 40 or 50 ch. It clinched the AR4CS title—the category specifically dedicated to the 4C, where other tuned models also compete. The engineers then concluded that the chassis had reached maturity.

The latest innovation: the RT1 wing

In 2020, the final step was the introduction of the distinctive rear wing. TEZZO engineers believe that the 4C, with its very short wheelbase, a relatively high engine center of gravity, a rather abrupt surge of torque from the turbo, and very wide track widths, is prone to twitchy handling with oversteer in fast corners. They therefore developed a true racing wing designed to generate rear downforce.

This spoiler, made of wet carbon with a hollow monocoque structure, weighs only 1.4 kg. A new internal reinforcement system has been added to Version 2 to prevent the trunk from deforming under high aerodynamic loads. Since the Alfa Romeo 4C’s trunk is not flat, TEZZO had to design custom mounts. Unlike many track-only spoilers, TEZZO wanted to ensure compliance with Japanese technical inspection standards. They present the spoiler as a tribute to their championship-winning car while ensuring it remains legally street-legal in Japan.

The results reflect this progress: 3 pole positions and 3 overall victories in 5 races of the 2020 championship, culminating in the SR (Super Race, the “elite” class) title in the Kanto Championship. To clarify, the championship is divided into regional championships (including the Kanto championship) followed by a national final. Having deemed the development phase complete, Tezzo switched to a FIAT 124 Abarth project starting in 2021.