Unfortunately, some breakthrough inventions were abandoned in their infancy, never reaching their development potential -- such was the case of the enigmatic 1972-73 Chaparral Firebird SSX racer. Chaparral, the Denver, Colorado-based company, entered the snowmobile market as a relative latecomer in 1972 with a 14 sled lineup. To establish Chaparral as a player in the booming marketplace, they mounted a factory racing team behind the Firebird SSX racer.
Auto racing legend and multi-time Indy 500 Champion Bobby Unser and Chaparral Engineers transplanted race car technology to create the first independent front suspension snowmobile.
These sleds by all accounts and definitions were hand built racers containing many one-off parts. Everything was designed to make the sled go as fast as possible around the race track. The tach mounted in the dash, which was a thin piece of aluminum riveted to the steel steering column frame.
Team Chaparral built two SSX models: a 440 and a 650. Both were high-revving free air triples with triple Kiehin float type carbs and triple tuned pipes pumping out maximum horsepower at about 9,000 RPM. The 650 was fitted with R65CR model carbs and produced 105 HP on a dyno while the 440 was fitted with R44CR model carbs. This setup was a departure from the popular Mikuni float type carbs. Most racers opted to go with a trio of Mikuni VM carbs because more information and parts were readily accessible. The engine featured unique webbed crankcase castings that eliminated the engine mounting plate. This allowed the engine to bolt directly to the chassis and cut weight.
The CDI ignition system featured three ignition coils mounted in a plastic box behind the jackshaft and steering column. The Comet 100 CJ closed face primary clutch credibly handled the torque from the high-revving engine. The transmission featured a driven clutch connected to a jackshaft that goes to a chaincase. The ’72 SSX was fitted with a mechanical disc, while the ’73 utilized a hydraulic Kelsey Hayes binder.
Like other race sleds of the era, Chaparral doggedly pursued weight saving measures. The sled measured 110 inches long and 37 inches tall. The tunnel and hood’s front side panels were constructed of aluminum while the belly pan and hood were made of fiberglass to keep weight down.
Without question, the most thrilling aspect was the front suspension. This suspension system was the predecessor to the Polaris RXL oval racer developed by Gordon Rudolph for the historic Polaris Midnight Express race team. Chaparral engineers started off with a wide 36-inch ski stance and built a suspension system unlike any other on the snow.
The front end had the same basic geometry on modern Polaris, Ski-Doo, and Yamaha ProAction System snowmobiles. It was a dual radius rod, coil over shock trailing arm front suspension with a torsion bar supplying about 5 inches of travel. The torsion bar traveled through the belly pan and attached to the radius arm bracket rather than the trailing-arm like on modern designs. The tie-rod connected to the steering arm in front of the spindle instead of behind, and the shock didn’t have an adjustable collar. Ball joint type ends connected the steering arm to the tie-rod and the trailing arm to the chassis at the rear pivot point. Large weight loads placed on the spindle brackets caused them to crack.
This crudely constructed, primitively designed system was the first to get the ball rolling in the snowmobile business. Today, all trailing arm snowmobile manufacturers are challenged to reduce and eventually eliminate scrub and bump steer. About 25 years ago, the inherent bump steer and scrub problems created by the front suspension’s rudimentary geometry severely hindered the sled’s performance on the race track.
The rear suspension was nearly as unique as the front. The rear had a conventional twin torque arm mounted to an outboard tunnel-mounted coil over shock. The design resembled the rear skid on the Ski-Doo Blizzard MX. The front torque arm featured no shock dampening – just springs.
In 1972, the SSX was introduced with an aluminum rear skid. The factory switched to a steel rear suspension in 1973. The rear skid provided 4 inches of travel. With the front having more travel than the rear, finding a handling balance was difficult. A fully cleated 121- by 15-inch track wrapped around the rear suspension.
The Chaparral team and Unser designed aerodynamic body pieces, otherwise known as "wings" for the SSX. The winged wonders were banned by some race tracks for safety concerns. According to Chaparral team racer Roger Janssen, "The Eagle River track thought the wings could be dangerous since they were about head height, so they wouldn’t let us use them. At speeds more than 35 MPH, the front and rear wings gave us the down force to really stick in the corners."
For 1974, Chaparral extinguished its experiment with the trailing arm front end sled and reverted to the commonly accepted leaf spring front suspension. But there was no going back, the ball had started to roll and soon the IFS concept would be firmly entrenched in the snowmobile world.
In 1975, Gilles Villeneuve debuted his hand-built trailing arm front suspension on the Skiroule factory racers. The following year Polaris introduced the revolutionary RXL racer. Team Polaris’ Jerry Bunke, Brad Hulings, Steve Thorsen and Jim Bernat made racing history, racking up an impressive list of wins and paving the way for the introduction of the independent front suspension trailing arm system on the 1980 Polaris TX-L Indy. SG
TIMELINE by Paul Johnson_______________________________March 1997
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