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August 5, 2009

Viper Story: Part 3

Before I jump into the next part of the Viper story, there are a couple of news bits I’d like to share with you. First our very own Randy Swenson has been recognized as mountain rider of the year for his performance in Thunderstruck 7, (link to see the new trailer for TS8), which also received the Oscar for extreme snowmobile film of the year. Congrats guys!

And for the go fast crew, it is official, Gilles Gagne and his G-Force / Lamtrac team have been officilally accepted by the Bonneville promoters and world sanctioning body, the  FIM to challenge the world speed record with their blown Apex streamliner during speed week  on the salt, September 20-26, Wendover Utah. He is silently hoping to break the motorcyle record of over 300 mph!

… The monoshock performance became the main focus for the ‘what’s next’ debate. Engineering finally concluded that the ill fated ‘boinger’ could not be massaged into an acceptable component leaving us with only one option, use the Pro-Action plus system. The domino’s started to fall in sequence. Without the long travel mono-shock the unequal length, rack-steer, front end plans died on the vine and next thing we knew our baby had morphed into an SXr chassis / suspension with a lightened up SRX motor. A long way from the original ‘all-new’ concept.

None of this helped to hit our weight targets which would have seen the Viper coming in significantly less than the SXr700 but how could it when it used the same chassis and suspension? The suspension eyeball was still aimed at a big bump / ditch banger target. The original testing criteria for the monoshock system was set to run a section of 3-3.5 foot bumps spaced at 20 to 40 inch intervals running a steady 35 to 45 mph…sitting down! The gentleman from sales who was adamant about this is no longer employed by Yamaha so I can say this… buddy you were outa your gourd!

I have learned when speaking with many sledders, the moguls they describe are often scaled similar to their manhood, where the three foot bumps they’ve been riding all day are really a foot and a half at best. Regardless, once a target has been established we don’t mess with it and when the monshock went away the ProAction really had its work cut out for it.

We had several years of tweaking the Pro Action system and as we all know, there is no magic setting to offer a plush ride and still resist serious hits. It was explained to me once that the first 8 inches of suspension stroke was fairly progressive but became linear towards the latter part of the travel then digressive as it fell through itself at the end. Think of it this way, riding through a series of 1-2 foot stutter bumps with the suspension stroking under ten inches, life is pretty good, staying flat and plush, that’s progressive. Now bomb down a smooth hill with a g-out at the base pushing the skid deep into the stroke and hit a small frozen pine cone, suddenly it bottoms hard and unexpectedly, loosening up your back fillings and sending that unmistakable tingle up your spine (that’s the digressive part.) ouch!

It was this severe bottoming that could break stuff and in the case of a bump sled, needed to be addressed.
Whenever the spring rate was stiff enough to limit the bottom out, ride comfort suffered. Engineering was reluctant to use multi-rate springs and position compensating valving and Kayaba had certain limitations to settings if there was a chance of bending the damper rods. In the end the short center shock received some very stiff compression damping and the stiffest spring we had. The ride wasn’t plush but it could take a pretty good hit. But, as fate would have it, someone made a change to the front shock spec after final testing / pre-production sign-off and before production.  I have not been able to find out exactly who or why but the first production units started showing cracks in the hoods, which after investigation, was credited to over damped front shocks. Instead of the small bump energy being absorbed, the shock remained rigid and all the rattling went into the chassis. At the same time the stiff front end was being kicked up by the bumps which were now coming into the center shock farther back and effecting the coupling point making the already stiff rear end even less compliant…

saitoIn the next segment I’ll focus not so much on what we had intended to build but what we brought to market and how we positioned it. I spoke to Masa Saito (seen in this Alaskan fishing trip photo) earlier this week and he promised to dig up some development stuff when he is at factory later this month. I have some interesting documents from the research and marketing side to sprinkle in. cheers cr

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Posted @ 2:56 pm in Sled Development   

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5 Responses to “Viper Story: Part 3”

  1. Ike says:

    Great reading once again Chris! Oh, what a sled it would have become without the problems of the consumer version of the mono…. Shame. I´m glad that the mono did come available. It´s great. Needs more durability, but it´s still a great suspension with the E-öhlins.

    The Viper engine is still one of the nicest triples around. It´s smooth, powerful and has the best sound of the triples (sorry, can´t beat the ole quad under the Vmax-4 hood though).

    You guys still have any parts of the long travel front ? I could use some on our project here….

    Keep up the good work CR!


  2. Flatlander SE says:

    Excellent story. It answers all the questions I’ve had concerning the race sleds during that time.

    It goes to show that it’s never as easy as it seems(from the consumer perspective).


  3. Yellowknife says:

    Thumbs up on the article Chris!


  4. Yammerhead says:

    Very interesting. You haven’t mentioned it yet, but did you feel the motor met expectations? I believe the Viper HP ratings were closer to the 600’s, rather than the 700 twins of the other OEM’s. I never owned a Viper, but looking from the cheap seats, it seemed that the interweb buzz was more about power (lack of) than how stiff it was sprung. Actual owners and their lumbar vertebrae may say otherwise!

  5. Scott says:

    I’m enjoying this series of articles, good work!

    Also, regarding the digressive rate in the final inches of travel on the Pro-Action, does that mean Polaris is actually correct in their marketing that the Pro-Ride rear is the first truely progressive rear skid? I had been thinking BS since Ski-doo marketed their skids as progressive back in the mid-80’s on the PRS chassis.

    Now I’m wondering?

    Hey Scott, I’m not the expert on this but I have learned a few things. Consider the nature of the beast. When the suspension system is contained within the track it must fold into itself as the stroke is compressed By the time you have used up all the travel there is no real estate left for the hardware to live regardless of the geometry and layout. It seems to me that by moving the linkages outside of the skidframe, it allows the engineers the room required to have the angles yield a progressive rate (more mechanical advantage against the force as stroke decreases). As far as Polaris being the first, hmmm looks an awfully lot like a glorified SnowSport to me 😉

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