Honda’s Software-Defined Race Cars Learn On The Fly

In 1982, Honda Racing Corporation (HRC) was established as a separate subsidiary and in 1993, Honda of America established Honda Performance Development (HPD) to look after motorsports activities in North America. Salters joined HPD as chief engineer and engine technical leader after 20 years working on Cosworth engines for CART and head of F1 engine development at Mercedes-Benz High Performance Engines and then Ferrari. In 2020, Salters was named president of HPD.

At the beginning of 2024, HPD became HRC US as Honda sought tighter integration of its global racing efforts. HRC US retains primary responsibility for the IndyCar engine program, the Acura ARX-06 GTP program for IMSA and off-road racing. HRC global handles all of the motorcycle racing including MotoGP, World Superbikes and Trial racing along with other four wheeled efforts such the F1 power unit program for Red Bull and Racing Bulls. HRC is also developing a new power unit for the 2026 rules that will be run by Aston Martin.

These days, top-level racing has become vastly more specialized than it was back in 1958 when Honda-san entered the Isle of Man TT. There’s less movement of staff directly between motorsports and production programs than in the past. Instead, the integration of HRC US has resulted in some staff rotating through F1 programs in Europe and Japan.

Software Defined Race Cars

At a media dinner with Honda following the Detroit Grand Prix last June, I got into a fascinating conversation with Salters about software in race cars. The IndyCar and IMSA prototype programs are the two best known efforts currently run by HRC US. In recent years, both have followed the lead of F1 and adopted hybrid power units. But unlike F1 where the power units are completely bespoke to each manufacturer, these units rely on spec hardware to help contain costs. On the surface, that may not sound very interesting from a technical perspective.

But as every engineer knows, applying constraints to a problem is what drives innovation and creativity. Take for example modern Bugattis like the Veyron and Chiron. These are amazing machines. But they are essentially unrestricted from a cost and price perspective. The engineers had almost free reign and while these cars are insanely luxurious and fast, that largely comes via applying brute force in the form of quad turbocharged 16-cylinder engines. There’s nothing especially innovative.

A Lotus Elise on the other hand was designed with price, weight and performance in mind. That led to the development of an innovative structure comprised of aluminum extrusions joined with new industrial adhesives. Sure it’s not as fast as a Veyron but it sure is fun to drive and technologies developed for the Elise have since been applied widely across the auto industry.

The Endurance Racers

The ARX-06 is built to the LMDh ruleset which was conceived by IMSA. It is one of two distinct regulations that qualify for competition in IMSA’s GTP class and the Hypercar class in the FIA World Endurance Championship. Other cars built to these rules include the Porsche 963, BMW M Hybrid V8, Cadillac V-Series.R, Alpine A424 as well as upcoming competitors from Genesis, Ford and McLaren. There are specific aerodynamic and dimensional rules for these prototypes and they have to use a core chassis from one of four approved suppliers, Multimatic, Dallara, Ligier or Oreca.

The other prototype ruleset is the Le Mans Hypercar or LMH class. In LMH, manufacturers have a bit more freedom to build their own chassis and powertrain with or without a bespoke hybrid system. Currently Toyota, Ferrari, Peugeot and Aston Martin are competing with LMH cars with the Aston being the only non-hybrid. The aerodynamic restrictions are largely similar for types with a defined lift to drag ratio of 4:1.

Manufacturers in both LMH and LMDh are free to use any internal combustion engine they want but it in LMDh it must be paired with a gearbox made by XTrac, a motor generator unit from Bosch and a battery from Williams Advanced Engineering. The nominal combined output of the engine and hybrid system is 670-hp for both car types and the minimum weight is 1,030 kg.

IMSA and the FIA have a process called balance of performance (BoP) that is intended to get all the cars into the same performance window regardless of which ruleset or powertrain they run. The organizers get real time telemetry data from all the cars when they are on track and prior to races, they can make BoP adjustments that adjust the power, torque and weight up or down from the nominal amounts. Before one of these cars can race, it must go through a homologation process with the FIA and IMSA that includes on-track and wind-tunnel testing. Once a car has been homologated, the specification is locked in for a period of five years. The manufacturer can make a limited number of design changes during the homologation period for performance improvements and they are also allowed to make changes to address safety and reliability but they must be approved.

There’s also one more important restriction. The GTP/Hypercar rules define a virtual energy tank and a maximum amount of energy that can be used per race and per stint. The virtual fuel tank consists of the volume of liquid fuel plus the maximum amount of electrical energy that can be used per stint before the car must pit and a maximum that can be used in the race.

This creates an interesting optimization problem for the engineers. While you could make a race car that used more energy to go faster, it would have to pit more frequently and the time standing still and going in and out of the pits amounts to ground lost on the track. A car that can go further between pit stops is likely to cover more laps in a 2, 4, 6, 12 or 24 hour race so efficiency is beneficial. But if you overdo it on efficiency, you might lose maximum performance.

Notice that there was one element that wasn’t restricted – the electronic control systems. While everyone uses the same battery, gearbox and motor-generator unit, they can all decide how to manage the balance on their own. HRC uses an electronic control unit from F1 loaded with bespoke software with the hybrid system in the ARX-06.

LMDh is now in its third season and HRC and its competitors have learned a lot about how to make the best use of the hardware that they share and the results can vary quite a bit. Think of it as though you may have the same brushes, canvas and paints as Pablo Picasso, the results of your work may be radically different.

According to Salters, it’s not simply a matter of regenerating kinetic energy into the battery and releasing it to reduce fuel consumption during acceleration. The engineers are using that electrical energy in a lot of creative ways to both improve raw performance and also enable the drivers to extract the maximum performance from the car.

If you’ve ever looked into the cockpit of a modern race car it’s a shockingly complex environment. The ARX-06 steering wheel has 20 buttons, four scroll knobs, a full-color display and several paddles on the backside for shifting and the clutch. There’s also a whole other panel of buttons on the right and assorted switches and displays around the cockpit. There’s a lot for the driver to do and besides steering, accelerating and braking, most of it involves interactions with the software.

Agile Development in Racing

Engineering in motorsports has always required a degree of the type of agility that has become common in software development in the tech industry in the past couple of decades. It’s always been common for engineers and technicians to be designing, fabricating and trying out new parts during the course of a race weekend in an attempt to eek out a bit more speed from the machine or make it a bit more driveable.

Today, one of the most important groups in a racing organization like HRC is the software engineers. Salters shared that for the ARX-06 they are regularly releasing software updates every weeks, days or even hours. In the course of a race weekend, there may be multiple software dates between practice and qualifying sessions right up until race time.

One of the lesser known aspects of the ARX-06 is that the compute system is actually running simulations in real time while the car is on the track. It’s taking in data from all of the sensors in the car including wheel speeds, tire temperatures and pressures, brake temperatures, accelerometers, the usual array of engine sensors and the torque sensors that are on the axles. Those torque sensors are mandatory under the rules as part of the telemetry package for IMSA, but the engineers can use them to ensure that they are getting as close as possible to the allowable torque output without exceeding it, which would incur a penalty or disqualification.

In addition to just outputting raw torque, the motor generator unit is also used to do things like preloading the differential which can be used to impact the handling of the car. These cars also use brake by wire systems and the software also manages the brake balance in real time. In the old days, drivers in many types of race cars would have a lever to adjust the brake bias from front to rear depending on if they wanted more understeer or oversteer. Now the software does this and can make adjustments from corner to corner based on how the car is behaving. Based on the results of the simulations, the parameters can even be adjusted over the course of a drive stint as fuel is consumed and the weight changes.

Of course the drivers have a say in this as well through that complex interface on the steering wheel. Sports car racing involves anywhere from 2-4 drivers per car depending on the race and each may have their own driving style and preferred behavior of the car. When one driver gets out during a pit stop and another gets in, they are often adjusting settings to their liking as they get buckled in.

While F1 teams may come to each race with physical updates that can include new wings, sidepods, floors and even suspension systems, prototypes don’t have this luxury but the performance can still change pretty dramatically over time depending on how well that code performs and how well the drivers are able to take advantage of those updates.

Hybrid Indycars

IndyCars are another class of racing that puts significant limitations on what can be changed on the car. The open-wheel Dallara DW12 has been in use since 2012 and is now on its third aerodynamic update. All teams are required to use the same cars and there are two notable areas that they are allowed to modify. One is the dampers and the top teams in the series all have active programs to try to improve the dampers to maximize the handling and grip.

The only other mechanical variable is the engine. For the past dozen years, there have only been two manufacturers involved in supplying IndyCar engines, Chevrolet through its partnership with Illmor and Honda through HRC. Chevrolet and Honda have made regular updates to the 2.2-liter twin-turbo V6 engines they supply ever since they were first introduced in 2012 that include both mechanical and software changes.

The biggest powertrain change to IndyCar since 2012 happened in mid-2024 when a new hybrid system was launched into production. As in LMDh, it’s a spec hybrid system that was jointly developed by the two companies. Chevrolet/Illmor took responsibility for the motor-generator unit while HRC developed the energy storage system (ESS). Because the whole system was developed to go into the existing car, it had to be packaged to fit within the bell-housing. Due to the limited space available, the ESS consists of super-capacitors instead of a battery.

The system development was originally intended to be done by some suppliers, but after they ran into problems, Chevrolet and HRC took over the project and developed the hardware in just 10 months before locking it in. HRC wrote most of the software and then shared it with Chevrolet. Unlike the ARX-06 software the IndyCar hybrid system doesn’t go through as much of a continuous development cycle.

The nature of the type of car and how the system works creates interesting challenges for the drivers. “How do drivers use it in a smart way? Because it affects the behavior of the car,” said Salters. “A – how do they regenerate in the right places, deploy in the right places, get performance from it?”

Super-capacitors have much lower energy density than batteries but very high power density. Thus a small unit can deliver a lot of power but only for a very short period of time. In order to help the drivers, HRC does a lot of simulation work to understand the impact that the ESS has. This helps the drivers figure out when to regenerate energy and when to release it for a burst of power.

Since the current engines debuted, the cars have had push to pass that gives them up to 120 seconds of overboost to use during the course of a race much as the F1 drag reduction system helps provide a bit more acceleration and speed for passing maneuvers. The IndyCar hybrid can be used in the same way and it’s capped. However, timing when to regenerate is crucial because the car will lose speed. It also changes the braking balance because the energy is all pulled from the rear wheels.

Not all of the drivers have been particularly enthusiastic about the hybrid system since it debuted. In the recently concluded 2025 IndyCar season, one driver seemed to be able to take better advantage of it than others – Alex Palou who won his fourth championship in five years in the most dominant way yet. Palou won 8 of 17 races including his first Indianapolis 500 and had the championship wrapped up after just 15 races.

“If you’re driving these things fast, this car is on the limit of traction, rotation, all these sorts of things to get the most out it. And that’s the skill of a World Class driver,” added Salters. “So you’ve got to do that, and then you’ve got to be thinking about how I may use the hybrid system.”

In the Indy 500 where top speeds on the straight can approach 240 mph, messing with the balance of the car can potentially have devastating effects.

“So you can be drafting a car. You can start to regenerate. The driver has control of it, ready, ready to pounce on the car in front. We actually made that system where the driver has significant control of it so they can use it for racing, for attacking or defending. And I think you see that really, the champions are able maybe to extract a bit more. They’ve just got a bit more capacity, bandwidth, I don’t know, whatever, whatever makes a champion.”

“So they, sometimes we notice that they can be doing it in different ways than some of the other drivers that maybe aren’t, maybe they can be maxed out just driving the car, and which is still a massive achievement, and then trying to get the last, the last half percent out of everything. That’s what differentiates a champion.”

“They’re all superbly good. Who can squeeze the last half percent out of five or six things to give them a percent or 2% advantage, and the hybrid comes into that. So watching someone like Alex, that is really, as you can see, sort of the class of the field this year. He seemed to squeeze more out than some other people, maybe. But you know how he used it in terms of balancing the car, or used it for racecraft, it was quite interesting to watch.”

Many people aren’t crazy about the concept of spec racing, preferring instead a more open rule book that allows more technical creativity. As an engineer, I love the idea of a minimal rule set that lets new ideas flourish as ground effects, and turbos, and crazy fuels did in F1 in the 1970 through the 1990s. But ultimately that becomes more a competition for the engineers than the drivers. If a driver is stuck with a car that doesn’t have the latest design concept or went down the wrong path, even the best will be left behind.

On the other hand, constraints also lead to creativity in engineering. Just because the engineers can create some cool new technology, in a race car like an IndyCar or LMDh prototype, it’s ultimately just another tool in the kit for the drivers and those teams that work together to figure out the best way to use the tools can come out on top.

What About Production?

This story started out with Soichiro Honda and his philosophy of using the constant pressure of motorsports to make his engineers better at creating products for the road. In the 21st century, motorsports has become vastly more complex and sophisticated than it was in the 1950s. The skill sets required to be at the top in the highest levels of racing whether it be MotoGP, F1, sports cars or IndyCar take more time to develop.

But that doesn’t mean there is no technology transfer to the road. Honda conducts an annual symposium in Japan where engineers and researchers from across the company including HRC gather to present and publish papers on their developments. In recent years that has included some of the engineers working on software for F1 power units, LMDh hybrids and IndyCar hybrids.

Honda isn’t generally one of the automakers that first pops to mind when you think of the software defined vehicle. But the company has been developing and releasing new features for its vehicles that rely heavily on software to create new capabilities. Among those is the i-VTM4 torque vectoring system on the new Passport Trailsport. This uses the same torque-vectoring hardware that has been at the core of the Acura Super Handling-AWD for nearly two decades but with a completely different control strategy that turns it into a virtual locking differential for off-roading. While this probably didn’t emerge directly from the racing efforts, I wouldn’t be surprised if the Asimo OS that is debuting on Honda’s upcoming new EVs benefits from some of the lessons learned in how to develop software rapidly at the track.