Long End Blocks & Adjustment

For many years Polaris sleds were the easiest to adjust the rear suspension torsion springs. This was due to the “open” blocks on the front of the springs, down on the suspension rails. You could just flip the sled on it’s side, lift the long end of the spring up and out of the open block, unloading the short end of the spring up in the adjuster cam. This way you could adjust the cam by hand, with no tools, as long as the snow and ice let you access the adjuster cam.

While this made for quick and easy preload adjustments, it was discovered through competitive environments that a ski tip (from behind) could lift the long end of the spring up and out of the block, and this was bad deal out on the race track. Polaris reacted appropriately by installing a safety pin and retainer clip across the top of their revised open blocks, still allowing the same method of adjustment by requiring the removal of both the clip and pin to do so.

Now we’ve seen the expansion of using the exact point of contact to tune the suspension. The first instance of this we saw was on a custom sled built by Dale Cormican, using Renton Titanium torsion springs and adjustable long end blocks to provide a multi-rate to the spring force. Tri-City Polaris also offers blocks that vary the contact points and provide a dual-rate to the displacement curve, very popular on Polaris RMK models. And in 2005, Yamaha integrated a similar feature into many of their latest torsion spring suspensions, with a three-position adjuster located further back on the rails from the primary spring holder to provide an anti-bottoming effect.

All of these systems vary the amount of spring force as the suspension moves through its range of travel. Typically, what we see is a higher rate being applied at the later portions of travel to prevent “hard” bottoming of the components. They all allow for more precise tuning of the suspension springs to better match the riding conditions and rider weight, as well as provide a greater perception of comfort. Think of it as somewhat of a “position sensitive spring rate”.