1st Thing to do when adjusting snowmobile suspensions.
Make sure the machine is on level ground preferably concrete floor or even a trailer surface, also make sure the spring adjusters will turn freely weather be threaded adjusters or cam style with the notches for the front ski and center shock and make sure the torsion spring adjuster blocks will rotate. Also make sure the machine is free of extra weight (snow, luggage , dogs or anything else ) .Also before any real changes are made if this is new sled to you I would strongly encourage you know the condition of your shocks the last service and who they are setup for (stock, revalved). Why? If one shock is dead or the oil is well used and past its service life you will be chasing your tail all season trying to get the sled to ride and handle correctly. You may be able to make and achieve all these spring and ride height adjustments but without a damper that is working correctly it will do absolute no good. Why set the machine up? If the machine is properly sprung and or the springs setup correctly you will be using all of the available travel the machine has. So think if you hop on the sled and it sags down 4” , you have now taken your 12” of travel and reduced it to 8” so with the 8” you have left you must have that shock firm enough to absorb and not bottom out in that 8” of travel. You must have preload on the suspension to suck up ruts and other holes.
Start with the Front.
Start by setting the front static sag. The best method of finding static sag is :
1.) Place a jack under the front of the machine and lift it so the skis and suspension will be extended fully but so the skis do not leave the ground.
2.) Next back off your springs until there is as little tension as possible on the springs. (you do not want the spring to rattle around on the shock )
3.) Measure front the ground to a good reference point on the front of the machine (Bumper, lower a arm bolt or even bottom of the frame)
4.) Let the machine down slowly and that reference point should drop approximately 2” for most riders. If it does jack the machine back up and put more tension in the springs until you achieve that 2” static sag number. For a firmer setup that will bite a little harder in the corners you can run up to 1” of static sag.
5.) *If these numbers are not achievable chances are good you will need resprung, this can be do to dyeing spring, extra accessory’s, age or just a poor setup from the factory*
Front track shock, FTS
1.) Jack the rear of the sled up or put it on a stand so the track is not touching the ground.
2.) This is an adjustment that is best adjusted in the field doing test and tune. While the sled is up make sure the spring will spin easily. Sometimes its easier to just remove the fts all together put it on a bench and
free the spring adjuster. This will make your life much much easier and less time consuming in the field trust me.
3.) The purpose of the front track shock is to allow the machine to transfer weight. Think of it as the pivot point in a seesaw with more weight over the front of the sled.
- A) The more spring tension you add to the front track shock the less weight over the skis and the less bite and less steering effort which can cause what is referred to as pushing in the corner. It will also cause the sled to transfer more weight and lift the skis easier.
- B) The less spring tension you put in the front track shock the more pressure the skis will have on the ground also causing heavy steering and less weight transfer during acceleration.
4.) Each sled chassis likes a different amount of spring in the front track shock. Riding the machine is essentially the best way to find this setting. Each model will have the factory setting measurement in the service manual.
USE CAUTION WHEN MAKING ANY LIMTER STRAP CHANGES – this is usually a last resort.
1.) Limiter straps are the rough or large adjustment to the fts, so if you’re not getting the desired results out of the front track shock spring, (Weight transfer, ski pressure and the shock is good) then you can go after the limiter strap adjustment.
- A.) Loosening the limiter strap will cause less ski pressure, more weight transfer and less steering control
- B.) Tighten the limiter strap will cause more ski pressure, less weight transfer and more spinning and heavy steering.
2.) It’s not often i run into a situation where limiter straps need changed from the factory settings which can be found in the service manual.
*NOTE* this setting is best to start off at the factory setting and adjust from there.
Rear torsion spring adjustment rear static and race sag.
1.) With the machine on level ground still lift the rear of the machine slightly until the suspension is topped out but don’t lift it off the ground, take your first measurement from the ground to the rear bumper, now let go of the rear bumper and let the machine sit for a second, you should have roughly 1-2” of rear static sag.
2.) If you do not have that, adjust your rear torsion blocks to get the desired results.
- Race sag 1.) This is the amount of sag in the rear suspension with a rider on it.
- 2.) While still on level ground repeat the first steps in setting of the static sag, next sit on the sled measure from the ground to the bumper while sitting on the machine, you are looking for 3.5-4.5” of sag with a rider on the machine from the initial measurement. If the machine sags more or less than the 3.5-4.5” adjust the torsion blocks accordingly.
*NOTE *after making changes to any area you should go back through and check that the original measurement remained true. A rear suspension torsion spring or fts spring adjustment can affect the front ski spring sag measurements.
All of the shock adjusting info will be quite a bit different between machines, since a Polaris Indy sp or Skidoo tnt will have no adjustments on any shock from the factory there isn’t any shock tuning to do to these models, where as a Polaris pro s will have compression adjustment and a skidoo xrs will have single/dual speed compression adjustments as well as rebound control.
Lets start by identifying compression clickers, and rebound clikers.
1.) Compression clickers will be located at the body end of the shock or the bottle attached via a hose to the shock , it is controlling the flow of oil displaced by the shaft as it enters the body when the suspension is compressed.
2.) Low speed compression is called this because it refers to the speed of the shock shaft NOT the actual speed of the sled. So a long gradual bump or when you sit on the machine or cycle the shock on the bench by hand is low speed. This is more for initial ride comfort or plushness. It will increase the firmness of the shock and will cause the shock to become softer. The low speed is Usually the inner knob or flat head adjuster on the compression adjustment.
3.) High speed compression has only started to become more popular in recent years on consumer sleds but this refers to a large fast hit like a square edge bump that will casue the shaft to enter the body fast. Usually the high speed compression is the outer position of the compression adjuster (Red outer nut kyb/hpg , red knob walker evans .
*NOTE* When turning the outer portion (high speed) the low speed adjuster will turn with it, that’s ok and is not actually adjusting the low speed only the high speed
4.) Compression is used to keep the machine from bottoming out during the travel of shock. If you keep finding the bottom of the suspension during a hard ride you need to add more compression or firm the ride up.
1.) Rebound clickers are located on the shaft end of the shock on the eyelet itself and is usually a red knob or flat head style adjuster. The rebound will affect the compression circuit of the shock because it is using a rod through the center of the shock to control the bleed circuit.
2.) Rebound is the speed and control of the shaft exiting the body, so if you hit a bump in the rear and it feels like you’re going to be thrown over the front of the sled that would be rear main shock rebound needing slowed down.
3.) Skidoo KYB pro40 shocks use rebound and compression, if you’re not able the achieve the amount of compression your after try backing the compression off 4 clicks and add 2 clicks to the rebound circuit and see if it improves .
Final notes and tips.
This sounds odd but while riding it can be difficult to tell if the suspension is to firm or to soft. Sometime you can get the feeling the shocks are to firm, when in fact your riding so far down in the stroke of the shock your not using any travel causing it to feel firm and its actually to soft or the springs are not properly adjusted.
TIP: you can use very small zip ties around the shaft, while riding you can see if you are using all of your available travel or how much travel your using. You want to use it all your shock travel on large hits, if the shocks are to firm and you’re only using 3 of your 6 inches of travel what good is the rest.
If you’re having issues with diving in the corners or excessive body roll in turns try adding (increasing) a few clicks of compression and see if it improves , a lot of that can be caused by the compression being too soft and the shock compressing in the corner causing that body roll feeling.
This cannot be emphasized enough, if you’re chasing an issue of handling or ride quality, it might be wise to think about the last time the shocks were serviced. This is usually the number 1 issue I see with machines. And if you bought a new to “you” machine (USED) and the seller says they were just serviced , have him produce some type of documentation or call the shop he had them serviced at to verify this. Because you cannot physically see if a shock has been serviced sellers use this as a selling feature that a lot of times was never performed.
Also a lot of beginner shock builders are not aware certain shocks take certain weight shock oils, and a shock that might take a 5 weight oil in Amsoil might take a 10 weight oil in Belray oil. Shock oil viscosity (Weight) is not consistent across brands of oil so a lack of compression can be caused by wrong oil or if the oil is too heavy for the valving this can cause excessive heat and cavitation as well as a lot of ride quality issues.
Last but not least ass the shop setup in the world doesn’t replace what works for you on the trail, my butt dyno is not the same as your butt dyno I may like it firm you may like it soft, if you like a firm setup or a soft setup that is all rider preference and there is no one that can tell you how you like your ride.
I hope this will answer some questions and or get you on the right track for getting the most out of your sleds suspension. Further questions, tuning or insight feel free to contact me Travis Clabbatz at TK’S Shocks 814 397 0347 or email firstname.lastname@example.org