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SEBRING, Fla. — Alexander Rossi piled up 134 laps in the Dallara IR28 on Tuesday, Nov. 18, at Sebring International Raceway, capping the busiest day of on-track work for IndyCar's 2028 prototype since its development program began. The run followed a fuel system issue that had limited Alex Palou to 43 laps the previous day.
The IR28 has now completed three testing rounds spanning seven days. In its first two appearances, on the Indianapolis Motor Speedway road course and oval, the objective was simple: prove that the car's basic systems functioned as intended. Sebring was a different kind of assignment. This time, IndyCar and Dallara told the drivers to stop treating the machine like a showpiece and start driving it like a race car.
"The messaging we get is run the car as if it's your race car," Rossi said. "From there, we'll see what issues, problems, surprises come out of that."
Rossi, the 2016 Indianapolis 500 winner, said the early checklist items had already been completed in the preliminary tests. The Sebring outing, he explained, was about practical application: how does a prototype behave when asked to perform like a proven, race-ready machine for hours at a time?
"I think all the test list items were really accomplished in the first two tests," he said. "Just making sure things worked as you would expect. This test is more of a practical application of: 'Does it perform over a two-day test as the current car does? Does it do what it is expected to and kind of what little things could come out of that we need to address before the series produces a bunch of these?'"
Sebring is a deliberate choice. The old airfield circuit has long been viewed as the most brutal permanent road course in North America, with rough concrete joints, abrupt pavement transitions and the kind of bumps that can shake a car loose from its setup. IndyCar does not race here, but the circuit is a cherished testing venue for teams from IMSA — which stages the legendary 12 Hours of Sebring — and other major series.
Rossi, who knows Sebring from sports car racing, offered a blunt assessment of why the track belongs in this development program.
"What's good about this place is it's the poorest-quality surface that you can have in a permanent road course," he said. "It mimics a street course kind of. Because it's a permanent road course, it gets used a lot, so it's a higher grip level than a street course. In terms of bumps, pavement changes, difficult changes in the asphalt, that's why everyone comes and tests here. It's somewhat of a preview that you're going to get in street courses."
The workload alone made Tuesday a useful stress test. Multiply Sebring's 3.74-mile circuit by Rossi's 134 laps, and he covered roughly 501 miles — nearly the distance of two standard IndyCar road or street course races. Every one of those miles came over a surface that punishes brakes, dampers, gearboxes and backs. The prototype's ability to complete the day without a major failure is a meaningful early sign of structural integrity.
The Florida heat and humidity added another layer of difficulty, and that is where the IR28 scored its clearest win of the week. Both Rossi and Palou came away impressed with a new cooling package for the cockpit. The change, Rossi said, was immediately apparent.
"Cooling-wise, we made a pretty big step in this test, in particular," he said. "It's night-and-day different in terms of comfort and drivability in the cockpit."
That praise matters beyond comfort. Cockpit heat has been a recurring complaint in the current generation of IndyCar machines, which carry more weight and generate more heat than their predecessors. Driver fatigue in high-temperature street races is a genuine performance consideration; a car that is cooler to drive is, by extension, faster at the end of a long stint.
The fact that two drivers with different teams and driving styles reached identical conclusions about the cooling arrangement gives the engineers a cleaner signal to work with. Driver ergonomics can be subjective, but when feedback overlaps, the design direction becomes more definitive.
The IR28 arrives with far greater institutional weight than a typical mid-cycle update. The current DW12 chassis has been racing since 2012, evolving through the IR18 bodystyle in 2018 and later gaining hybrid power. By the time the IR28 debuts in 2028, that old warhorse will have carried the sport for 16 seasons — an extraordinarily long lifecycle in top-level motorsport.
The name itself signals the program's timetable, following the same convention that produced the IR18 for 2018. Consistent naming across chassis generations is rare in open-wheel racing, where platforms often carry multiple monikers over their lifetimes.
The next big checkpoint is already on the horizon. Dallara is scheduled to deliver additional IR28 chassis to Chevrolet and Honda in late 2026 or early 2027, allowing each manufacturer to begin integrating the next-generation engine and hybrid components with the new platform. Once those production-representative cars are in the hands of Chevy and Honda, fundamental alterations to the chassis become far more difficult and costly.
That makes every test day before that handover precious. The IR28's record through seven days of running is an encouraging one: no significant component failures beyond the fuel system issue that interrupted Palou's Monday running. By the standards of prototype development — a discipline in which early test cars frequently spend as much time in the garage as on track — that is a rapid maturation rate.
There is also a practical reason the series wanted a long, rough day at Sebring specifically. The street course rounds in Long Beach and Detroit present many of the same surface irregularities that Sebring does, and a car that survives Florida's shattered tarmac is a car that can cope with downtown streets. Rossi called the session a useful preview of the hardest races the IR28 will face in its first season.
For now, the priority is data. Dallara and IndyCar will spend the coming weeks reviewing telemetry, suspension load readings and driver comments from both Sebring sessions before deciding what adjustments are needed for the next test. The findings will shape the evolution of the prototype as it moves toward its production form.
Rossi, for his part, sounded satisfied with a day in which the car did everything that was asked of it — and asked plenty. In a development program, the quiet days can be the most valuable ones. For a car still two years from its first green flag, Tuesday was exactly the sort of quiet, busy day that builds the foundation for 2028.
