Understanding The Modern Mountain Snowmobile Rear Suspension
Most snowmobilers have little or no understanding as to what a rear suspension does other that allow the track to rotate around it. They have no clue how it works and why a properly tuned rear suspension can make your sled go better than the next guy’s sled.
It’s kind of like the black art of clutching. So we have provided some questions and simple facts to help you understand how they work and what to do to make improvements.
How Does A Rear Suspension Work?
A snowmobile rear suspension is the most complex suspension of any powersport machine. There are two slide rails that support the length of the track with a bunch of suspension-looking parts tucked in the middle. The suspension has two arms that connect from the sled’s tunnel to the slide rails with a shock on each arm to control them independently. The front arm controls the front to back movement of the rails to properly maintain the tension of the track as the suspension is compressed. The back arm is on a 3-point scissor arm so it does not interfere with the movement of the front arm but does carry the majority of the sled and rider weight. This allows the front and back half of the suspension to move up and down independently and change the angle of the slide rail accordingly.
How Does The Suspension React In The Snow When Riding?
As you ride, the suspension moves up and down in the front and back independently to keep the length of the track on the snow without bridging the gaps to maximize traction. When you go uphill or punch the throttle, the power of the engine and the angle of the hill cause the weight of the sled to transfer to the back portion of the suspension where it gets the most traction. The movements are fine-tuned with the proper combination of suspension mounting point, arm length, shock valving and spring rates. These are all things that the sled manufacturers and aftermarket companies like Timbersled have figured out through the years. They are calibrated to what we think is the perfect ingredients to a suspension that works well in the backcountry and offers a smooth ride on the trail.
What Should You Do To Make Your Suspension Work Better Than Your Buddies’?
Today’s modern suspensions are fairly good in comparison to a few years ago. However, there are several things you can do, from improving your stock suspension to replacing it with an aftermarket suspension.
Sleds come from the factory set up with a universal calibration that will work decent for the masses. They have very little tuning adjustment. The first and cheapest thing to do is get your spring rates set to your body’s weight (including the 30 lbs. of gear you pack in your backpack and on your sled). Most OEMs will have options for different spring rates from softer to firmer; ask your dealer for a recommendation if the chart does not specify rider weights.
The second thing is with the combination of the proper spring rate you can re-valve your stock shocks to match the new springs. There are only a few select companies in the mountain sled industry that can do this properly.
The third option is to replace the shocks on your stock suspension with a custom tuned set of aftermarket shocks that have added external adjustments such as compression and rebound adjusters.
The fourth option is to replace the suspension with an aftermarket one. There are several companies, along with Timbersled, that specialize in aftermarket suspensions.
The aftermarket suspension will offer all of the above shock improvements and added adjustability to get the sled on top of the snow faster while providing an even smoother ride than the stock suspension is capable of (even with aftermarket shocks).
Aftermarket companies can do this with improved geometry to best fit our design and added adjustment that the OEMs don’t do, due to the manufacturing cost and keeping the product simple and easy to use.
What Will These Upgrades Do For You In The Mountains?
A stock suspension that is not calibrated for your weight can cause trenching when you take off from a stop or climb a hill. It will also make your sled ride rough on the trail and can make for a bad-handling sled.
If the suspension is too soft, your sled will sit low to the ground when all loaded down with snow and will trench because it has lost all of its ground clearance and will drag on the running boards. It will also ride rough down the trail because you have very little suspension travel left and it will potentially bottom out on bigger bumps.
If it is too stiff, it will trench and the track will spin and feel like it has no traction because the suspension is not moving enough to keep the track evenly weighted on the ground to maximize traction. It will also ride rough simply due to the suspension not moving easily to comply with the bumps.
Aftermarket suspensions can work much better in a lot of conditions because they have different geometry and can stroke the shock at different speeds at certain points of the travel to help increase traction and improve ride quality.
For example, the front shock and arm can be made with a higher pre-load pressure but have a more linear spring rate to better hold the front of the sled up but have a softer ride through the bumps, making your sled feel less bouncy. The back shock can be made to have a softer pre-load without having a bunch of static sag like stock suspensions. It can have a more progressive compression rate to hold the weight of the rider.
A lot of aftermarket suspensions also feature a suspension coupling, not found on stock suspensions. This is what the Timbersled Mtn. Tamer suspension specializes in. Coupling will control the amount of transfer your sled gets. It does this when the weight transfers to the back of the suspension.
When the coupling takes over the back arm will mechanically pull up the front arm a monitored amount, depending on how you have it adjusted.
Two beneficial things happen when it couples. First, it flattens the front approach angle out and keeps the track parallel to the ground where it can get the most traction by using more paddles on the snow while resisting trenching. The second thing it will do is keep your ski close to the ground when climbing a steep hill, giving you more control to steer when you need it. Coupling works amazingly well on a stock sled and is mandatory for a turbo sled to get the power to the ground while maintaining control.
How Should You Make A Decision On What Will Work Best For You?
If you are buying a new or used sled, first ride it and then make changes. Weigh out your options because you do not want to spend a bunch of money on shock upgrades if you plan to buy an aftermarket suspension later on because aftermarket shocks for the stock suspension will not fit onto an aftermarket suspension.
Also, if you plan to install a turbo and want to make suspension modification, your best money spent will be for an aftermarket suspension that has the ability to control higher horsepower.
At the end of the day, after you have made your suspension improvements, you could have the advantage over your buddies.
Like we say here at Timbersled, a good working suspension is like having traction control when everyone else doesn’t.