Internal Drivers

"Dear Ralph" January 18, 2006 0
Dear Ralph: My brother-in-law says I should switch my 2001 Summit 700 to an external drive system. He says I would gain more horsepower...

Dear Ralph:
My brother-in-law says I should switch my 2001 Summit 700 to an external drive system. He says I would gain more horsepower from less resistance. What the heck is he talking about?
Darren Schmitdke

He is referring to the drive sprockets on the drive axle, and how they engage the track. Your sled uses internal drivers, as most sleds have for what, nearly thirty years now. The drive sprockets engage lugs on the inside of the track belting that transfers the power from the engine and drivetrain to the track.
This type of drive system does require a specific amount of tension on the track to keep from jumping a cog, or “ratcheting”.
Earlier snowmobiles used an external drive sprocket design, where instead of using internal lugs the “teeth” of the drive sprocket came through the open windows of the track, thus the term “external” drivers. This method doesn’t require as much track tension to keep from jumping a cog, and is the main attraction to power-starved high-altitude riders.
There are other differences between the two methods, but this one is the reason we now see some of the latest mountain sleds going to an internal/external drive sprocket. By allowing reduced track tension, the rolling resistance of the system is reduced. Think of it as taking your foot off the brake. When the track turns easier, there is less resistance to overcome and ultimately there will be more power transferred to the track instead of being wasted overcoming friction.

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