When the wraps came off the Mazda RT-24P at the LA Auto Show last November, many observers were struck by the new IMSA sports-prototype’s swoopy good looks. Driven by the demands of aerodynamics – specifically, the need to force air over the now-mandatory over-wheel cutouts that reduce the risk of a racecar taking flight – LMP1 and LMP2 racecars in the World Endurance Championship (WEC) and beyond have become more square-fronted in recent years. But not the Mazda, whose more rounded profile takes inspiration from the LM55 Vision Gran Turismo virtual racer, the late-lamented Furai concept and Mazda’s Kodo – Soul of Motion road-car design language.
The RT-24P slots into IMSA’s new, unified Prototype class in the WeatherTech SportsCar Championship, which combines LMP2 chassis built to global FIA regulations with a Gibson-made, spec-V8 engine, and IMSA’s own Daytona Prototype international (DPi) cars. The DPis, of which Mazda is one of three current manufacturers (Cadillac and Nissan are the others), are based on the global LMP2 standard – in Mazda’s case, a chassis from Multimatic-Riley – but incorporate styling tweaks to enable road-car manufacturers to put their own stamp on the designs. Different engines can also be used – the Mazdas are fitted with the MZ-2.0T, a 2-liter turbo I4 made by AER in the UK – and certain parts changed to make it simpler to operate the cars in North America.
Tech spec: Mazda RT24-P
Length: 4,750 mm (15.41 feet)
Width: 1,900 mm (6.23 feet)
Wheelbase: 3,022 mm (9.91 feet)
Weight: 930kg (2,050 pounds) without driver or fuel
Top speed: Approximately 200 mph
Brakes: Brembo calipers/Hitco carbon discs
Dampers: Multimatic/Dynamic DSSV
Transmission: Xtrac 6-speed sequential with paddle shifters
Tires: Continental Extreme Contact 320/680 R18 (front) and 325/710 R18 (rear)
Wheels: Motegi Technomesh forged aluminum
Fuel: IMSA E20
Fuel capacity: 75 liters (19.8 gallons)
As per DPi regulations, the bulk of the RT-24P’s chassis is standard LMP2 and therefore shared with the Riley Mk.30 being campaigned by Visit Florida Racing in the WeatherTech Championship, but is very different from the aging, Lola-based B12/80 that Mazda ran last year.
“I would say there’s pretty much nothing carried over,” confirms Zach La Grone, lead engineer for SpeedSource. “They’re both prototypes with rocker-actuated suspension and third springs, but that’s about it. The geometry and the hard parts themselves are completely different – some of that is dictated by rules changes, some from what Riley has learned over the years, and some from what Multimatic was able to contribute.
“The suspension uses a rocker setup that’s unique among the LMP2 car manufacturers,” he continues. “The concept is carried over from earlier Rileys but the geometry and parts are all new. With the ‘Riley Rocker,’ the spring and damper are attached separately to the rocker. That enables you to have differing motion ratios between the spring and the damper. It’s an interesting layout. You end up with the spring and damper running laterally across the car instead of longitudinally as you’d have seen on our Lola.” The dampers are Multimatic’s own DSSV items, with Hyperco springs.
Driver-adjustable sway bars will be a very interesting feature that this car has going forward. Now that we have them, it’s a level playing field -Zach La Grone, SpeedSource
The electric power steering was developed by Riley from a KYB rack and power assistance system. Brakes come courtesy of Brembo calipers and Hitco discs, as on the LMP2 car. To lower the center of gravity, the front calipers are sited at the bottom of the upright, F1-style.
Motegi forged-aluminum wheels are fitted with the Continental tires that are standard in the WeatherTech Championship. The process of learning a new car has been complicated by the introduction of a new tire, the P2500, for all 2017 races except Daytona. The pre-race test at Sebring in late-February was the first opportunity for SpeedSource to run the new tire on the new car – which was itself running for the first time in high-downforce trim – so there is considerable work still to be done by all teams to learn about the new tire during the season.
Engine spec: Mazda MZ-2.0T
Displacement: 1997.6 cc
Bore x stroke: 90 mm x 78.5 mm
Power: 600 bhp
Max engine speed: 8,500 rpm
Head: DOHC, four valves per cylinder
ECU: Life Racing
Turbo: Garrett Motorsports, air-to-air intercooler
Fuel injectors/pump: Bosch Motorsport
Fuel rail: AER
Styling and aerodynamics
The source of those distinctive looks is Mazda’s design studio in Irvine, California. Beginning in May 2016, a small team led by Ken Saward, senior manager of design, sketched the concepts that would lead to the RT-24P’s final look.
“We wanted it to be like LM55 or Furai,” says Saward, “with a much more voluptuous shape with a beautiful silhouette, similar to racecars of the 1960s and ’70s, where the front end was much more swept downward to the floor. Meeting those requirements was our biggest challenge.
“The big areas we got to play with were the front and rear fenders and the sidepods. We pushed a little bit further to get some treatments for the front end, the nose specifically. There was a crash box in the front end that we had to build around to keep within the regulations. We also had to keep the WEC cabin, which is much taller than our Lola’s. We had to figure out ways to hide its height and visually we played with graphics to do that.”
Sylvain Tremblay worked with a digital designer at Mazda on details to help the team get the look they wanted, but also meet the aerodynamic regulations and requirements. The digital design was then transferred to Multimatic, which built the DPi’s body, for further development and CFD testing. Mazda also sent staff to the UK to work alongside Multimatic aerodynamicists on the design.
Styling-wise it was a big departure from what everyone else was doing, but aerodynamically it worked quite well -Ken Saward, Mazda
Alongside the CFD program, a 40 percent scale model of the RT-24P was also tested in the Penske tunnel in North Carolina.
“One thing we struggled with last year was pitch sensitivity,” says La Grone. “Multimatic worked hard to improve on that. The Lola was an old car and there’s some natural development and progression, combined with the regulations, that Multimatic was able to use to improve the overall drag and downforce numbers.”
Balance of Performance
In addition to the in-house test programs of Mazda and the other DPi manufacturers, IMSA has undertaken a comprehensive program of Balance of Performance (BoP) evalution in order to ensure aerodynamic and engine parity between the spec-LMP2 cars and the DPis, whose incorporation of road-car styling cues entails small compromises in aerodynamic performance. Working for IMSA at the Williams F1 wind tunnel in the UK, aerodynamicist Ben Wood’s Dynamique company designed its own, 40 percent scale LMP2 wind tunnel model against which to baseline the various LMP2 and DPi bodywork styles. Each of the bodies (the three DPis, plus the four LMP2s) was rapid-prototyped, fitted to the 40 percent model and tested to establish the relative performance of each.
In November 2016, IMSA brought the actual cars to the Windshear full-scale tunnel in Concord, North Carolina for further testing. “The type of runs that we do, the aero maps that we use are essentially the same at 40 percent scale and full scale, with good correlation between the two” says Mark Raffauf, director of series platforms at IMSA. “The model step enables us go into the full-scale tunnel to look at specific enhancements to individual cars, in order to offset the performance deltas.”
Those enhancements draw on a toolbox of elements from the LMP2 aero kits such as Gurney flaps, dive planes, side wickers, barge-board shapes and splitter tips. IMSA set the initial BoP before the Rolex 24 and will revisit it as required through the season on the basis of comprehensive data logging and analysis. “The process works and is now in place to accommodate any new DPi manufacturer over the next four years,” says Raffauf.
The Mazda RT-24P ran for the first time on track in a private test at Carolina Motorsports Park in Kershaw, South Carolina, close to Riley’s base, shortly before Thanksgiving in 2016. The first public running was in the first week of December at Road Atlanta, followed by IMSA’s December test at Daytona, where a gearbox cooling issue came to light.
That was fixed in time for January’s Rolex 24, but unfortunately for the team, after running reliably for most of its duration, both cars retired near the end of their debut race.
“The #70 car had a gearbox failure that stemmed from an issue with the clutch system,” explains La Grone. “That led to it not fully disengaging the clutch before shifting into gear at pitstops. Over time that broke the gearbox but the failure came at an unfortunate time with only 20 or so minutes left in the race.
“The #55 car had an oil line rub through. It’s one of those new-car packaging things that had never been an issue in testing up to that point. Some stuff is difficult to get a hold on until you run consistently for 20 hours – it took us 20 hours to have a problem and when we did, it was a big one in a hurry, and there was no fixing it in the time we had left. Even so, we’ve rectified that by revising some of our plumbing and cooling to be more serviceable and reliable ahead of Sebring.”
The 12 Hours of Sebring on March 18 will be the first time the Mazda has raced on the new tire and in high-downforce trim, with the addition of two dive planes and a change to the piece underneath the dive planes above the splitter, which is now pocketed out instead of the smooth, drag-reducing Daytona configuration. There’s also a Gurney on the rear wing to aid rear downforce.
Like every other Prototype, the Daytona-winning Cadillacs included, the RT24-P will benefit from every additional minute of running as the teams learn more about their new machines through the WeatherTech Championship season, which concludes at Road Atlanta in early-October. Having already collected a substantial amount of track data to correlate its models, Mazda also has a driver-in-the-loop simulator program planned with Multimatic, to enable it to explore setup options away from the track.