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Tech Notes: Suspension Innovation

Snocross ‘shock war’ intensifies!
When Bobby Unser invented independent front suspension for the Chaparral racers back in 1972, his main goal was to use hydraulic shock absorbers to control ski motion. At the time the standard of the industry was leaf spring suspensions. The action was mostly undampened, although attempts were being made to mount hydraulic shocks at a very flat angle next to the leaf spring. The problem with this setup was that only a very short travel of the shock shaft was possible, therefore limiting dampening action.

■ Engineered on the track

More successful were perhaps the PACS friction shocks which Mike Trapp used on his 1971 and 1972 championship sleds. With the PACS, you had two arms acting in a scissor action with friction pads between them as the arms moved. Bobby was involved with this design together with “Pappy” Holnagel of Mechanical Industries. The scissor arms aided in stabilizing the ski action and preventing the skis from bending under in turns, but the friction action could not be tuned with a different compression and rebound action. When Unser’s IFS design was adopted by the Polaris Race Team, the race for a more controlled suspension began.

■ Improve, race and repeat
Early shocks were often standard automotive Monroe units, probably chosen for their low price rather than outstanding dampening properties. They were still a large step up from the leaf spring with limited shock travel. Most trail riders were happy with their new IFS suspensions but racers were soon on the hunt for better shock absorbers, and that challenge continues today, with factory race teams continuously developing more sophisticated shocks on the Snocross, Cross Country and Enduro circuits. Today’s shock absorbers are light-years ahead of the early Monroes – both very sophisticated in their tunable circuitry, and now also stone reliable.

The competition between Ski-Doo’s KYB team, the Polaris Walker Evans team and Arctic Cat’s Fox shock team is at full-pitch all year long, with special factory support teams at all the races. In the early ‘80s, the main challenge centered around oval racing, where the tracks were smoother, but quick reacting shocks would give an edge in cornering performance. The obvious go-to sources at the time were road racing and motocross motorcycles, who were looking for both consistent dampening and shocks that would not fade and lose their dampening action as the race went on, especially in long races.
Wicht and his Swedish Ohlin shocks helped his racing sled stay consistent on the track during endurance races.
As the continued hammering from bumpy motocross tracks heated up the shocks, the oil would start to “boil” and produce air bubbles that would reduce the dampening action. The first attempt on a fix was finned aluminum bodies for better cooling, but this was not very effective. The next step was the Girling Gas Shock, which basically was an emulsion shock where the fluid was pressurized with nitrogen, in order to move up the heat range before the oil “boiled.” The amount of pressure you could use in emulsion shocks was limited, and finally full gas pressure shocks where a floating piston that separated the high pressure gas from the oil was found to be a workable solution that kept the oil from “boiling.” With the separate chamber, pressures up to 300 PSI could be used. With the floating chamber dividing piston still in the body and a nitrogen-filled space above it, the shock body needed to be longer.

The next step in the evolution was to move the pressure chamber outside the body, to a reservoir, which allowed a larger oil volume and also could result in a shorter shock or longer stroke. Today the outside reservoir is either part of the shock body, best known as a piggyback construction, or as a true remote reservoir connected to the shock via a flexible hose and mounted independently on a frame part some distance away.

■ Swedish ingenuity
The first really good high-pressure shocks were the Swedish Ohlin motocross units with separate reservoirs. Ohlin was contracted by the European Yamaha Race teams, both for motocross and road racing, and they paid for three full-time race support teams with technicians assisting drivers at the track. They also had a fourth team on the U.S. motocross circuit. This intense development program greatly improved both the quality and performance of the Ohlin shocks. Yamaha later bought a controlling interest in Ohlin and much of the expertise was then transferred to their KYB production shocks.

In the ‘80s, my company, Aaen Performance, was the U.S. importer of Ohlin shocks for snowmobiles, which quickly gave us an edge on the racetrack. Tim Bender and Darcy Ewing soon won both F-1 and F-3 oval races with the high pressure gas shocks. John Wicht was possibly the biggest beneficiary of the Ohlin shocks. He won four SOO I-500 Enduro races with them, all while running the whole race solo with no relief driver. The SOO I-500 race usually lasts seven hours and most teams use two or three drivers. When Wicht raced, other sleds were transformed into jumping pogo sticks after 100 laps as their shocks faded away.

Wicht’s strategy was to sit back for the first 100 laps. His sled was set up with a long-travel Snocross suspension, and when the track got rough, he could easily pass the other riders, and was usually in the lead with 100 laps to go. The Ohlin shocks were of great quality construction and did not lose gas pressure or performance at all. Wicht ran one set of shocks at the SOO I-500 for three years. When we finally took them apart and serviced them, they still had the original gas pressure, and the parts all looked new. We just put them back together and John ran them for several more years.
We tried to sell the shocks to both Polaris and Arctic Cat and although they liked the performance, the Swedes were way above the price the purchase department could justify. When Snocross racing hit its stride, the shock business instead went to Fox who grabbed onto the challenge and grew their business into the snowmobile market with steady innovations and developments. The original Ohlin shock was well made and of high quality, but had no outside adjustments like today’s shocks. They stuck with a steel shock body because they could produce a very fine finish for the Teflon rings on the piston to run against. The steel bodies also expanded less when hot, keeping the clearances close and the performance consistent. The piston had shim stacks on each side for compression and rebound and they could be tuned by building stacks of different thickness and diameters shims. This made the shocks speed sensitive, increasing the dampening power. Early competitive gas shocks usually used aluminum bodies with a hard coating for the piston running surface. This coating often deteriorated, resulting in loss of performance and a need for frequent rebuilds. Today’s modern aluminum shocks use a new and better Kashima coating. These new shocks are light years ahead in both performance and quality.

■ Better now than ever

Today’s intense Snocross pro circuit has greatly advanced shock technology over the last 10 years. Snocross shocks now have to control 10 inches of ski suspension travel and up to 15 inches of rear track suspension travel. Shock bodies and pistons have also grown in size. KYB bodies are 46mm (1.8 inches) all around, while Walker Evans use 51mm (2.0 inches), and only Arctic Cat uses 38mm (1.5 inches) on front with their Fox air spring Evol 3 shocks, for a very light package. All the shocks are high pressure (250-300 PSI) piggyback shocks and have outside adjustments of both compression and rebound circuits. The compression valving usually has a low- and high-speed adjusting circuit with up to 24 clicks on each, and the rebound adjustment circuit may also have up to 24 positions.

The only shock that does not usually have a rebound adjustment is the front track suspension shock, because this shock is shorter and the adjustable rebound circuit takes up an additional inch of length in the shock eye. The adjustment circuits only fine-tune the shock, so the baseline compression and rebound forces are still controlled by the shim stack calibration on the piston itself. The new shocks also have a position-sensitive feature. This means that as the shock nears the end of its travel it needs additional dampening when the spring forces increase. This is controlled by a bypass circuit that is active as part of the calibration in the first 70 percent of the stroke. There can be holes in the wall connecting into the piggyback and the adjustable compression circuits as in the Walker Evans shocks, or spiral grooves in the body as in the Fox shocks. At the 70 percent point, the piston passes the end of the bleed passages, and the last 30 percent of the stroke then gets a harder compression dampening.

With full factory support, development at the Snocross racetrack is intense every weekend. Fox has a Midwest development center based out of Brainerd, Minn., that does production as well as race calibration for the factories. The manager is Rick Strobel, who has four support vehicles crossing the country, two with shock dynos available. Their Snocross support team consists of Mike Japp and Dan Ebert. The Walker Evans race manager is Ben Hays, son of ‘70s Polaris and Mercury factory driver Doug Hays. Ben started working as race mechanic for Polaris under Tim Bender, then worked for several years with Rick Strobel at Fox, and finally moved back to the Polaris race shop in Wausau. Ben is supported at the races by two technicians from the Walker Evans factory and they all work out of the Polaris support transporter. Ski-Doo and KYB support is handled by Tim Zakarias and assisted by engineering and technicians from KYB often working out of the Scheuring and Warnert Transporters.

This year is a new challenge for both Ski-Doo and Polaris as Arctic Cat jumped them with the longer 136-inch suspension and track last season. Both Polaris and Ski-Doo now have 136-inch tracks and new suspensions that need to be calibrated. Preparations for upcoming races have been intense and fans are eager to see how the new and longer track suspensions perform for Ski-Doo and Polaris in the saga of the Shock Wars.

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