1978 Arctic Cat SnoPro
The history of Arctic Cat is littered with both production and race sleds that incorporated new thinking to make better riding and better handling snowmobiles. It all started with the first slide rail suspension in the mid 60’s. Track suspension evolution continued through the mid 70’s with lightweight aluminum construction and adjustable front torque arms to improve weight transfer. Ski suspension was also under scrutiny with various leaf spring ski designs and canted steering to allow the skis to tilt into the corner.
While Cat was acknowledged as the suspension leader in those days, a new independent front suspension had snuck under the radar at Thief River Falls. Complacency perhaps? The wakeup call would happen in mid December 1976 at Ironwood, Michigan.
Roger Skime with a mint specimen of the 1978 Arctic Cat SnoPro
Arctic Cat had just come off a dominating season in ‘76 winning the SnoPro title with their race sleds, which many consider to be the ultimate leaf spring race chassis. That winter Team Arctic and the rest of the big four race teams had come up against Gordon Rudolph and his Independent Front Suspension (IFS) sleds. The Villeneuve Brothers had built new Skiroule racers that were fast around a corner, but still fragile and hard to handle. Polaris had taken notice and were busy building new IFS and leaf spring chassis sleds for the ‘77 season. Ski-doo had also taken notice and had built race sleds with IFS.
The Polaris juggernaut for the ‘77 season started that weekend in Ironwood and Arctic went home with their brand new race sleds that were now obsolete. Roger Skime and company went into damage control over Christmas and would have their first IFS sled on the racetrack at Hartford, Michigan in early 1977. It had taken Durmont Wahl and Dennis Zulawski less than a month to design and fabricate the 77-1/2 SnoPro racers. It would be a quick education into the world of bump steer, caster and camber angles and spring preload. Life was so much simpler with leaf springs.
While Cat was taking their lickings on the racetrack, Roger Skime reassigned a young engineer (Roger Gage) from Advanced R & D to the Race Department to design a new race chassis for the 1978 season.
The Z-Bar Front Suspension
Roger Gage had seen how touchy the steering setup was on the ’77-1/2 racers as the suspension moved through its travel. Thus, Arctic had set the following design criteria for the new front end:
i) Ski Travel: 5”
ii) Eliminate Bump steer to prevent skis from toeing in and out
iii) Keep weight to a minimum
Work began on developing Ackermann steering to work in conjunction with the new IFS design. While Ackermann steering is common in the automotive world it had seen limited use on a snowmobile. Gage worked out the geometry for the steering linkage and designed a new steering arm that allowed the Ackermann principle to work. Ackermann steering allows the inside ski to rotate further than the outside ski allowing the sled to turn sharper when cornering and prevent the outside ski from wanting to slide out from the corner.
We’re all familiar with the term “Bump Steer” which is when your sled wants to dart from side to side when traveling over bumps on the trail. In the infancy of IFS design, race teams were struggling with this phenomenon and it was catching seasoned pro riders off guard, resulting in some nasty crashes. The new Arctic SnoPro would have the steering linkages mounted parallel to the radius rods controlling ski movement. This design would limit bump steer.
Roger Gage had also learned that as a driver let off the throttle entering into a corner, weight transfer shifted onto the skis allowing some funky camber changes to occur. The result was a sled that would dart from side to side. The new Z-Bar front end minimized these camber changes making the sled less prone to bump steer.
The feature that gave the Arctic front end its name was the “Z-Bar” linkage. This linkage replaced the torsion bar (common on most IFS suspensions and still used today). Roger Gage wanted the front end of the new Cat to remain as flat as possible without losing contact with the track surface with either ski. The Polaris RX-L that was the class of the field in ‘77 used a torsion bar to control “body roll”. The stiffer the torsion bar was set the less chance of the inside ski lifting off the racetrack. Roger put pencil to paper and came up with a linkage that would couple both front skis together when moving vertically. This coupling would allow both skis to move in unison under load. Camber adjustments could still be made to compensate for flat or banked corners but the Z-Bar linkage allowed “machine roll” to be adjusted into the machine The sled was adjusted with a 2-degree slant of the front end towards the left ski. Rogers’s theory was the left (inside) ski compresses quicker than the right ski. The sled would drive into a banked corner and flatten the inside ski first to keep the sled and track flat on the track. Essentially, load the inside ski to keep it from lifting when cornering. It sounds complicated but pictures from back in the day show the Cats with both skis firmly planted on the ice while other drivers were still showing signs of inside ski lift.
We have covered the intricacies of the Z-Bar front end with no mention of the shocks/springs used. The race sleds back in the late 70’s were still running with oil filled shocks with absolutely no rebound or compression adjustability. Spring rates were the only adjustment available to adjust for rider weight and track conditions.
Arctic Cat has been a big believer in air shock technology, today and yesterday. Their new race sled arrived at the first race in Kinross, Michigan with Kayaba air shocks. Jim Dimmerman, who was a factory driver in those days recalls, “The shocks seals would leak once the air temperature dropped below zero. As the race progressed we would lose all the air pressure and the front end would collapse, causing the sled to under steer in the corners. In reality it snowballed the competition as they thought we still had a long way to work on our new front ends. We switched to coil over shocks after the first race.
Rear Suspension by Dennis Zulawski
Dennis Zulawski is a name synonymous with many of Arctic Cat’s innovations past and present. Dennis had been reworking the original Arctic Slide rail all through the 70’s and in fact his name is behind many of the “Z” race sleds. The ‘78 SnoPro Cat would see a new suspension design that is still used on some Champ 440 race sleds today.
Quick acceleration and the ability to go through turns with the power on is still a goal sought by race teams. The new track suspension featured an adjustable front torque arm that did not use a limiter strap as found on today’s sleds. Torsion springs controlled front arm movement with an adjustable front arm travel limiter.
The rear arm shocks and springs is where things got real interesting. Coil-over shocks, again with no rebound or compression damping adjustments, were located on either side of the tunnel. While not the first with this design (Skiroule was first) the shocks were connected to the slide rail through a linkage that essentially provided a wider support for the rails to prevent them from twisting under load. This design is better at holding the track flat on the ground for more traction under cornering.
Durmant Wahl and Dennis Zulawski
The increased adjustability with the twin shocks provided more flexibility with setup. For example if the sled was pushing going into the corner, the left side shock spring tension could be increased to put more load on the inside rail in combination with increased front ski pressure. The front and rear suspensions now were more connected than ever before in terms of improving cornering speeds. External shocks also reduce unsprung weight to improve response time of the suspension.
Style and Power
The 1978 SnoPro Cat was unusual looking to say the least. The styling of the sled was designed by Leon Raiter who designed many of the classic Cat’s. The boxy styling was functional and was given the nickname the “Mail Box”. Distinguishing features included the radiator location and the squared off air dam. The front air dam is reminiscent of Can-Am racecars of the day that were using ground effects for improved traction. The completely enclosed hood design protected the twin expansion chambers from snow and ice and kept the pipes warm to improve performance and consistency. Expansion chamber design was rapidly developing at the time. Arctic was now using Suzuki motors in three engine options (250, 340 & 440) to compete in all three Pro classes. Arctic clutching was used initially, with the switch made to Comet primary clutches later in the season.
Roger Gage had set out to design a lightweight race sled and the machine tipped the scales at just 325 pounds without using any exotic alloys. Mission accomplished!
Did it Deliver?
Team Arctic started the season with three drivers. Legendary Larry Coltom, Bob Elsner and rookie Jim Dimmerman. Coltom had a bad crash after the second race at Alexandria, Minnesota and hung up his leathers. According to Jim Dimmerman, this actually turned out to be a bonus for the team. Larry Coltom was a whiz with clutching so he worked as a development rider while the team was away racing.
Coltom also came up with the idea of slide rail lubricators. Jim Dimmerman recalls, “IFS required more track pressure on the front of the slide rails. The hyfax were heating up, slowing the sled down especially on the ice tracks, which were becoming more popular. Arctic was the first to install a slide rail lubricant tank on the rear of the sled to pump lubricant onto the sliders. This made a huge difference in top speed and was an innovation still used today.”
The clutching and setups Coltom developed that winter were quickly brought to the race sleds and by the midpoint of the season they started beating Polaris at its own game. Bob Elsner would end the 1978 season as the high point driver.
The Z-Bar chassis would be the platform used by Arctic Cat and Scorpion ‘till Arctic Cat went out of business at the end of the 1981 season. Bob Elsner won the World Championship in 1979 and Brad Hulings won on a Scorpion in 1981. Jim Dimmerman would race his Phantom race sled with the Z-bar chassis and beat the Ski-Doo Twin Trackers in 1984 at Eagle River, claiming its third World Championship.
Innovation Continues
The 1978 Arctic Cat SnoPro ushered in Arctic Cat’s continuous improvements of front and rear suspension designs. The Z-bar never made its way to a production sled but the A-arm suspension pioneered by Arctic in the mid 80’s addressed many of the shortcomings of a trailing arm suspension. The outboard mounted shocks for a track suspension was used in production applications in the mid 80’s and was picked up by some of the competition for production sled applications also, as the long travel suspension designs hit high gear in the late 80’s.
Arctic Cat learned their lesson the hard way back in ‘77. Never stop innovating!
By Hal Armstrong – SnowTech Canada
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