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Suspension

Complete Light Weight Bolt in Skid Suspension Kits

Nytro   Apex

Fabcraft Rear Suspension

See photo in catalog for more details!!!!

This is the best designed complete bolt in skid in the market today.  This skid bolts into all factory mounting holes. 

  • 17 degree approach angle that stops the trenching. 
  • EXIT coil over shocks or upgrade to Fox air shocks.
  • Weight saving 20-30 lbs. depending on model of sled.

 

Custom Built Complete 162” skid at 38 lbs.                      $2470.00

 

 

 

YAMAHA Pro-Action Rear Suspension

After years of dealing with the Yamaha Pro-Action system (a true parallelogram suspension with two way coupling) we have found it to be very finicky, and that an incorrectly adjusted suspension will cause a terrible ride (ratcheting, binding or bottoming) and possible suspension damage. One of our main concerns and the number one problem is an incorrectly set up suspension that when compressed the stroke or rearward travel of the slide frame exceeds the inner diameter of the track binding the suspension, and eventually something has to give. This will cause damage ranging from broken drive axles, bent tunnel or shock mounts, to bent track adjusters. All these form an improperly adjusted suspension. It is CRITICAL that you adjust the suspension AND track to factory specifications. Here are some we use for our Mountain Max 700’s. The front limiting strap adjustment 25-30mm.The factory maximum is 35mm (pulled up) and minimum 10mm (let out). This is measured from the tip of the adjustment bolt to the plate the bolt goes through. The upper gap in the control rod 10mm. The factory maximum is10mm and minimum 7mm. Again we can’t stress enough the fact that you should be using the factory track and suspension limit specifications for your model suspension.

These are excerpts from an article that was published by Snow Tech winter 1997-98 issue. They can be contacted at (320) 763-5411 or (Editor@RaceRally.com) we highly recommend a subscription to the magazine.

The History of “Coupling” in Long Travel Rear Suspensions 

What is “coupling” of the rear suspension and why is it important? What is the difference between “two way coupling” and “one way coupling”?

Suspensions as a whole are nothing but a big bunch of compromises. We’d like the ride quality to be super plush over the small bumps and never bottom out over the big bumps. We’d love to hit the throttle and get total traction with the track not spinning a bit and be able to keep the skis an 1/8″ off the ground. We’d like the sprockets to never jump a cog in deep snow, but wear the hyfax at a nice slow rate. It seems as if anything you do to try to accomplish any one of these will compromise the performance in another area. It is all a matter of which combination you feel provides the best value for your applications, what works best for YOU but first a little bit of history.

Early bogie wheel suspensions were nothing more than track tensioning devices with very small amounts of travel. In some cases no travel at all. The first slide rail suspensions pioneered by Arctic Cat started with about 3″ of travel and the ride was improved. When they went to 5″ things again got better, but when the travel went above 5-6″ the ride didn’t necessarily get any better. As engineers kept adding more travel, all the way up to 10″ and 11″, the ride quality didn’t seem to really improve. No matter what the engineers tried, the vehicles didn’t seem to work as well as they wanted them to.

Angle Of Incidence

After developing quite a few suspensions that didn’t hit the mark it was finally decided that limiting the “angle of incidence” of the slide rail as it hits a bump was the key factor to further improve the ride quality and make the longer travel suspensions perform. (The “angle of incidence” describes the angle of the slide rails to the ground as it hits a bump. As the front section of the rails hits a bump, the front of the rails rise but the rear of the rails are still at the bottom of the bump, causing the rail to be presented at a specific angle – the angle of incidence. The greater the size of the bump, the higher the front arm will raise and the greater the angle of incidence.) The greater that angle is, the more secondary kick there is to the rider when the rear hits the bump and the greater the loss of control there is to the rider, and greater the loss of speed of the vehicle. Herein is what was limiting the long travel concepts prior to “coupling”. It is called many different names, but keeping the slide rails as parallel to the chassis as possible was the answer. The ideal solution was to be able to carry a specific amount of weight (vehicle plus rider plus energy of the impact) on the rear of the suspension yet be able to limit the angle of incidence. How do you do this? One of the easiest ways to limit this angle was to put a very soft spring in the rear of the suspension. The problem with this solution was that when you land off a jump on the tail (of the sled) the rear of the vehicle bottoms extremely hard.

The next round of experimentation was to try to connect the two suspension arms (front arm and rear scissors) together by putting a sway bar between the two arms, and there seemed to be an advantage. The next step was to try to mechanically couple the arms together directly. The arms were connected together via some transfer rods and/or links and some experiments even used cables. There was a huge advantage noticed when the arms were coupled in this manner as the coupling was limiting the angle of incidence.

yamahaprotrak

Angle of Incidence This is where the parallelogram concept came into being, which all coupled vehicles are a variation. (Parallelogram meaning that if you have equal length arms and equal length bars the link has to stay parallel at all times.) By limiting the movement of the rear arm, both arms would move “together” as a parallelogram, even though only one of the arms actually encountered the bump. The end result is that the suspension rails remain fairly parallel to the chassis.

When to Couple and When Not To?

The timing of when you couple and not couple seems to be part of the magic of what makes one system work better than another. You should not be coupled at all times or the ride quality will be firmer than need be. In this case you are going right past the softer “un-coupled” portion of your travel and are loosing the best ride quality. This is why you can sometimes, on a coupled suspension, find that by increasing the pre-load of the rear springs that you will end up with a softer initial ride qualities. What is happening is that by increasing the pre-load you are moving the suspension away from a coupled condition to an un-coupled one, requiring some travel to get to the combined rate section of the travel.

If you don’t have rear to front coupling you have to increase the resistance to bottoming of the rear arm for the tail-landing situation. Consequently, when you’re not in a tail landing situation the rear arm spring and shock mechanism is stiffer than it needs to be (harsh ride quality). You likely can detect these qualities on those suspensions that do not employ this type of logic. By the same token, these suspensions lift the skis and really hook up well – if that’s what you want. What this tells us is that the suspensions that provide the best, coupled ride quality do not provide the best weight transfer. When you increase weight transfer on a coupled suspension, you will end up with greater amount of travel that will be softer – maybe too soft which could reduce the overall ride quality.

yamahatrak2

Yamaha Pro-Action Plus

The Yamaha Pro-Action Plus is a true parallelogram suspension with two way coupling. It seems to use a fairly linear rate of shock speed to rail travel. These units are very smooth and since they use a shock on both arms the suspension is able to retain its composure with a bit wider of an operating range into the rough. Still, it appears that in going for the comfort that Yamaha has traded off some of the high-speed control of the front arm. This trade off varies from model to model, but it seems to hold true through the line. In our mogul testing this was apparent, as the front arm would bottom when we pushed the units hard. There are also a fair share of links in this suspension, and while Yamaha has to be given credit for “sticktion” reduction techniques such as needle bearings and quality bushings, we wonder as to the logic of all the links. After 1998 they added a front bumper stop to the rails to provide greater control to bottoming as well as improvements to the center shock to provide better bottoming control. Some of the ’97s that were ridden in extreme conditions would damage the front shock, as there was no mechanical limiting device other than the rubber stop on the shock itself.

The “sliding gap” on both sides of the control rods performs the coupling function on this suspension design. As the front of the suspension hits a bump, the gap at the bottom of the control rods is closed, causing the rear of the rails to move up, keeping the rails fairly parallel to the chassis. In tail landing situations and during acceleration, the gap at the top of the control rods is closed. Once this happens, the front arm will travel up into the tunnel with the rear arm, effectively transferring part of the energy to the center shock and keeping the suspension rails parallel to the chassis.

Adjustments to the control rods take time requiring replacement or re-stacking of the plastic shims on the control rods. The second option is using after market quick adjustable type. The primary use of these quick adjust control rods is to get more weight transfer, however as the weight transfer is increased there seems to be a fairly proportional decrease in ride quality (the suspension will bottom easier). More weight transfer is obtained by providing a larger upper gap, allowing more weight transfer to take place before the arms are locked together. The Mountain Max versions of this suspension use only 2.5mm spacers in the upper gap for more weight transfer, while the XTC versions of this suspension use 10.0mm of spacers in the upper gap for less weight transfer.

 

 

updated 7/20/2016