With a total of three IFMAR world championship titles in electric sedan and nitro buggy classes, team HB is no stranger when it comes to finishing at the top of the podium. That experience is channeled directly into producing better race cars, including HB’s latest on-road machine: the PRO5. Like other competition touring cars, the PRO5 is built with an abundance of carbon fiber and aluminum alloy, and uses a pair of belts to deliver 4WD. It’s the details that set the PRO5 apart, and with 2006 IFMAR electric touring world champ Andy Moore contributing to the PRO5’s development, it comes as no surprise that the car is loaded with clever touches that make it more precisely adjustable and finely honed for success on the track.

PRECISELY TUNABLE SUSPENSION

Like any competition car (and most cars in general these days), the PRO5 has multiple holes for shock position and turnbuckles to set camber and front toe-in. From there, HB adds a bunch of fine-tuning options that include inner camber-link positions that can be moved closer or farther from the chassis’ center (via spacers under the ball stud mount) as well as raised and lowered (via spacers under the ball stud). Interchangeable aluminum hingepin blocks set front arm kick-up and rear anti-squat, and the aluminum steering knuckles get bolt-on carbon-fiber arms that allow arms of different geometries to be swapped in should HB change up the geometry. Out of the box, three Ackerman positions are standard. Swaybars are also supplied in three thicknesses, front and rear.

The PRO5 follows the current trend toward shorter shocks for a lower center of gravity, and HB specs very high-quality dampers. The threaded aluminum bodies have 10mm bores with anti-friction coatings and use bladders for volume compensation. Aluminum spring perches are standard. The shocks use a rubber bladder design to regulate the damping action and are secured in place with an aluminum/plastic hybrid shock cap. Hard-plated 2.5mm shock shafts are sealed by a pair of O-rings, and Delrin shaft guides prevent the shafts from scraping the aluminum lower caps.

The PRO5’s short dampers lower its center of gravity.

Vertical ball studs allow roll center to be changed with spacers. Note the two screws that hold the inboard ball stud mount. Varying the thickness of the spacers beneath the mount allows the ball stud to be moved laterally.

VARIABLE FLEX CARBON-FIBER CHASSIS

The PRO5’s carbon-fiber chassis is engineered to optimize flex for consistent handling. The double-deck design sandwiches machined-aluminum bulkheads between the 2.5mm main chassis plate and a slender 2mm top deck. A total of 11 screws can be installed to secure the top deck and adjust its stiffness—more screws, more stiff, and vice versa. To help assure the chassis’ torsional flex is consistent, the chassis is as symmetrical as possible—for example, the relief for the motor on the left side of the car is mirrored on the right. To prevent the steering servo from acting as a stiffener on the right side of the chassis, the servo is installed on a “floating” mount that suspends it from an arm attached at the chassis’ center.

DUAL-BELT SPOOL AND DIFF DRIVETRAIN

The PRO5’s dual-belt system is centered on the chassis, and the pulleys sandwich the spur gear for a very compact drivetrain that allows plenty of room for the motor and speed control on either side of the belts. The aluminum 20-tooth center pulleys and Kevlar-reinforced belts spin an oil-filled gear differential in the rear, while the front end gets a fixed spool. Eccentric bearing mounts indexed to fit the aluminum bulkheads set front- and rear-belt tension. Each end of the car gets universal-joint driveshafts. The rears are traditional CV-style with the addition of a plastic yoke that pads the crosspins on the dogbone ends. The front shafts feature double-cardan joints, or “DCJ” in HB parlance—basically two CV joints in a row. The benefit of a double-cardan joint is well documented in full-size vehicles, and the design allows smoother operation at greater turning angles as well as longer joint life.

The front driveshafts have dual joints for smoother operation while steering.

Dual drive belts straddle the spur gear and are centered on the chassis. Aluminum bulkheads hold the layshaft, rear diff, and front spool.

Ready for action. You’ll need to supply your own wheels, tires, and body.

BEHIND THE WHEEL

Cal Raceway in Orange, California, was my first stop with the PRO5. After a few easy photo-shoot laps and a little suspension tuning to get the car in the ballpark for the track conditions, I turned up the pace to scrub in the new tires. I wanted to see what the PRO5 offered in handling without using tire sauce or tire warmers, and I found the PRO5 was confidence-inspiring from the first lap. The box-stock setup gave the PRO5 a very neutral feel with a hint of push that made it easy to drive, and provided a good base for further tuning. I altered rear droop to allow more weight transfer to the front wheels, and the PRO5 responded with more aggressive steering. After a few packs’ worth of running at Cal Raceway, I felt satisfied enough with the car to test it further at TQ Raceway’s carpet track. HB boasts the PRO5 is a great performer on various surfaces, and ultra-high traction carpet is a great way to reveal a car’s true handling tendencies. Upon arriving, I swapped the LRP VTEC 36 asphalt tires I had installed previously for VTEC CPX carpet-specific rubber and sauced them with LRP’s Top Grip 3 tire additive. The PRO5 took to the carpet with ease, and I was able to drive it hard without significant changes from the stock settings. As the shock springs took a set with continued hard laps, the PRO5’s front end felt like it was allowing more roll than I liked. I swapped the manual-suggested 1.3mm front swaybar for the stiffer 1.4mm bar, which immediately showed results on the track as I dropped almost a full second off my lap times and the PRO5 sliced from turn to turn like a scalpel. Of course, a premium power system helps. I completed the PRO5 with a Tekin RS Gen2 speed control and the new Gen3 17.5-turn stock motor with the timing set at 30 degrees from the factory. It produced plenty of bottom-end torque coming out of turns but really shined at the higher end of the throttle curve, yielding fast high speeds that made it feel more like a modified motor. After a full day of asphalt and carpet action, I was very impressed with how well the PRO5 worked out of the box and its responsiveness to setup changes. It’s a versatile car.

FINAL WORD

Assembling the PRO5 was a breeze thanks to the clear, easy-to-understand manual, with the quality fit and finish of the parts being second to none. On the track, the PRO5 is competition-ready straight off the manual settings. Its track manners and ability to easily adapt to multiple surfaces make the PRO5 easy to drive fast. Its $500 price tag places it at the high end of the competitive sedan price range, but you do get a lot of car. I look forward to running the PRO5 in race conditions and claiming my spot on the podium.

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VEHICLE SPECS Item no.: HBS114500 Scale: 1/10 Price: $500 Weight, as tested: 2 lb. 15.6 oz. (1355g) CHASSIS Material: 2.25mm carbon fiber main chassis, 2mm carbon-fiber upper deck Type: Plate upper deck SUSPENSION Type: Lower H-arm with turnbuckle camber link Inboard camber-link positions (F/R): 1/1 (adjustable width) Outboard upper arm positions (F/R): 1/3 Shock positions, towers (F/R): 5/7 Shock positions, arms (F/R): 1/1 SHOCKS Bodies: Threaded aluminum, 10mm bore Shafts: Coated steel, 2.5mm Volume compensation: Bladder DRIVETRAIN Type: Dual belt 4WD Spur gear/pinion: 116T, 64 pitch/not included Differential (F/R): Spool/sealed bevel gear Driveshafts (F/R): Dual cardan joint/CV type Bearings: Metal-shielded ball + Solid handling on carpet and asphalt + Highly tunable suspension + Exceptional fit and finish - Expensive - Wheels not included SOURCES HB hpiracing.com Hitec hitecrcd.com LRP lrp-americastore.com MaxAmps maxamps.com Tekin teamtekin.com

TEST GEAR (NOT INCLUDED) Body: HPI Subaru Impreza Radio: Hitec Lynx 4S Receiver: Hitec Axion 2 HHR Speed control: Tekin RS Gen2 Motor: Tekin Gen3 17.5-turn Servo: Hitec HS-8775MG Low Profile Battery: MaxAmps 5450mAh 2S LiPo Tires: LRP VTEC G36 asphalt/VTEC CPX-V2 carpet Tire sauce: LRP Top Grip Charger: Hitec X1 Pro DC/DC Multi-Charger Paint: C-Built Designs

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TEST GEAR Hitec Lynx 4S A high-speed precision race sedan, like the PRO5, demands a radio system of equal caliber. I chose Hitec’s flagship surface radio: the Lynx 4S. Paired with the 2-channel 2.4GHz Axion receiver that uses “Hitec High Response” technology, the Lynx 4S’s commands are instantly executed. It also has a nicely balanced feel, and if you’re a lefty, converting for southpaw use is easy. In addition to every adjustment you need to dial in your car, unique features include variable mixing, a music player with headphone jack, and a model memory for up to 60 cars.