The Holeshot (Just for Buzz)
Getting off the starting line is crucial to winning in many forms of racing, from drag racing your buddies to sno-cross.  There are some basics that can help.  Traction, suspension, clutching and gear ratios will be the focus of this article.  Of course it is also important to have a torque-filled powerful engine, but we are going to concentrate on tuning the sled to utilize the power you already have.

The way you obtain good traction for your holeshot is dependent on the surface on which you are riding.  For snow, deep lugs are needed.  Ice requires sharp studs.  If the ice is soft, a few chisel studs may help.  Chisels also work for dirt or grass.  The following recommendations are made under the assumption that traction has already been maximized.

Weight transfer is a critical factor.  Because the center of gravity of a snowmobile is above the line of force, the point where the track grips the snow, ice or ground, the front of the machine rises upward when you accelerate.  The rear suspension should be set to capitalize on this principle of physics.  Two things should happen: The rear springs should compress and the center spring, front of the rear suspension, should extend.  The result should be a transfer of weight to the rear of the sled which pushes down on the track.  If the front end of the sled comes up too high a couple of bad things happen.  First, you have wasted energy by going up with the front of the machine instead of forward.  Secondly, the front portion of the track will not grip the surface well.  On the other hand,  if the front end does not come up at all, then weight has not been transferred.  This means that the skis are dragging and the track does not grip as well because there isn't as much weight on it.  If the rear suspension is set correctly, the skis should come up a few inches and the track should be flat on the riding surface.

This is accomplished by extending the limiter straps, increasing the preload of the spring of the front of the rear suspension and softening the rear springs.  There is no free lunch here, however.  These adjustments have a negative effect on your sled's ability to corner.  The inside ski will lift more readily.  If you are out drag racing with your buddies, soften the rear springs (softest cam setting or lighter springs) and let out the limiter straps enough so the skis come off the surface a few inches.  Now set the preload on the center spring, front of rear suspension, very stiff.  This will give the track good bite.  On the other hand, if you are riding the twisties through the woods, start sucking up the limiter straps until your sled corners to your liking.  A middle ground setting would be to keep the rear springs fairly soft, shorten the limiters until you can live with the corners and keep a high preload on the center spring.

Let's take a look at clutching.  The objective for clutching a snowmobile for a good hole shot is to utilize as much of the engine's available torque as possible without spinning the track.  Once the track breaks loose, traction is lost.  There is a lesson to be learned from driving a car on ice.  To get started it is beneficial to start out in second gear.  When we do this we have limited the engine's torque to match the available traction.  This is also true for snowmobiles.  Most sleds have ample torque to spin the track on take off on almost any surface.  We need to limit it, especially just as the sled begins to move.  This can be done in a number of ways.  The easiest is to adjust your drive belt lower in the secondary, which is like starting out in second gear.  Torque is force times distance, and putting the belt closer to the jackshaft reduces the distance, thereby reducing the torque.  This also means the primary clutch will slip more before it grabs the belt.  Belts won't last as long.

Another method is to install a different helix that will allow the clutches to shift to a higher ratio very rapidly at the beginning of the launch, but then slow down the upshift shortly thereafter.  This is done with a multi-angle helix.  A rule of thumb here is to have the first number about ten more than the stock straight-angle helix and the second number about two less.  Fine tuning can be done with the belt position and spring tension in the secondary.  For example, if the engine bogs, the belt can be raised in the secondary and/or the spring tension can be increased.  On the other hand, if the track still spins too readily, the belt can be lowered in the secondary.  You probably don't want to reduce spring tension because that will affect your backshift.  If the shift-out R.P.M. are changed this should be adjusted with changes in the primary clutch.  It can be done by changing springs: lighter to lower R.P.M. or heavier to raise them.  You can also add or subtract weight to the lever arms or fly weights.

Changing sprockets can also be considered.  A larger top sprocket will reduce torque.  This change will effect the entire pattern from low end to top end.  It will help limit track spin but probably will also reduce acceleration.  It may, however, increase top end.  Speed-run people like big-top sprockets.

These are some basics for tuning for a good holeshot.  Hopefully, they will be helpful as you attempt to fine tune your sled to meet your riding needs.  Good luck.