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August 10, 2008
Making smooth smoother
Both as a current franchise (Ski-Doo) dealer and consumer who has roots in motocross, I have always been interested in suspensions. Much can be written or said about a smooth or properly functioning suspension. With any manufactured product that covers a wide range of applications, there will always be consumers who will need (or want) to customize, pretty much regardless of what that product is.
That most definitely includes a snowmobile’s suspensions, which consumers want to better suit or fit their personal riding style and conditions.
After analyzing and considering the setups for our Ski-Doo Summits specifically, we have tried to identify some areas that may need rider re-evaluation. In this analysis, while it was Ski-Doo-specific, it could apply to other brands as well. This analysis included stock applications, i.e., what came on the sled from manufacturing, as well as aftermarket bolt-on applications along with what our company, Tom’s Snowmobiles and Service, offers our customers as options. All of the following information is our opinion and may or may not be agreeable to everyone.
1) Ski shocks and/or springs: In certain conditions the front end seemed to dive and/or was too soft. The front end rolls side to side too easily. On high-speed bumps, the front end felt too soft as well, bottoming out too easily.
Stock options include tightening or increasing spring preload, but that can affect sidehilling if over tightened and ultimately did not feel like it addressed the bottoming out issue of the front end at high speeds. Changing valving also could be addressed, but due to costs, we typically recommend that the customer purchase Fox Float air shocks instead.
Another stock option would include offering a slightly stiffer or higher rate spring. This too did not seem like the right choice for the customer, especially without reconsideration of revalving the shocks.
Removing the sway bar makes sidehilling easier, but has a negative effect on trails and high speed cornering. The sled’s front end can seem a little too roly-poly with this removed and stock shocks used.
2) Rear suspension, front track or center shocks: In certain conditions the stock setup appears to offer too much ski lift and/or continues to push the track out of the snow on steep climbs and offers too much track lift, detracting from a good footprint. Basically we felt the front track system was not giving our customers the desired results in our western Sierra snow conditions. While a controllable amount of ski lift is desirable, too much results in poor acceleration and performance. Our goal is to offer the rider more weight transfer control with his body movement than throttle position. We feel that this is an important area that we have worked on for the Ski-Doo suspension. This would also apply to other rear suspension designs from other brands.
3) Rear track: Torsion springs collapse too easily even when at a higher adjustment position. This appears to allow too much or too quick a weight transfer and also contributes to excessive ski lift.
For the most part, the rear torsion spring has been a manufacturers’ choice because of its ability to provide a relatively soft ride over the small bumps, yet offer bottom out resistance when contact with a large bump or big hit is experienced, especially at high speeds. The torsion springs provide a nonlinear spring force as the suspension moves from extended to a fully collapsed position as it travels through at an angular rotation. It is further intended to give or achieve a wider range of motion or dampening effect for a given degree of suspension travel, allowing for a significant rise in spring rate, which is much like how an air shock would.
Conversely, it is the inability of the coil-over design to have any significant rise in spring rate through the full travel or stroke of suspension that hinders its use in rear suspension systems.
The midrange of the rear shock valving moves too easily and/or strokes through too quickly, adding to the issue above.
The combination of all this translates into a tunnel that is now dragging or making contact with the snow, adding to frictional losses and/or drag on your forward movement. The end result is typically a sled that you thought would put a highmark on the hill but is not able to accomplish that.
4) In the aftermarket side of front ski, Fox air shocks in particular, we identified that the air chamber appeared to ramp up too high in pressure through full travel. It also appeared to be stiffly configured internally and/or too light of negative spring. In other words, there were also some problems with this shock as well.
There are, of course, other suspension options as well as rider preferences that could be discussed endlessly, but we have tried to quickly identify the highest profile concerns and procure alternatives as well as options for both our immediate customers as well as other consumers in the West.
With these concerns, or areas to address, we set our sights on finding a better and smoother suspension combination. At this time I cannot stress enough about the importance of looking at the entire unit to balance or carry out the duties of the suspension. Front and rear must work in unison for the rider to enjoy the full benefit of the suspension.
For the ski shocks, I did not spend a lot of time and energy on stock shocks. It was my opinion that it would be a better investment to improve the Fox Float air shock. Once we identified that we would work on improving the air shock, we analyzed what have been consistent rider complaints. The general consensus was that the air chamber ramped up too quickly. Though the shock did not bottom out, it had a harsh or uncomfortable ride in the slower speeds or beginning stroke of suspension travel. Overlapping issues also appeared or became evident. The shock valving and/or the piston design itself did not flow through the oil smoothly. The negative spring did not offer enough resistance to the initial main chamber air pressure. Our primary focus was to address the consumer complaints on Fox Float air shocks and correct these issues.
Left Wanting More
We were aware that several aftermarket companies were offering add-on air chambers to address some of the steep ramp-up issues of the air chamber, and this definitely helps, but we wanted more from this shock. We felt that though this was a step in the right direction it did not address all the issues with the air shock. Through our research with Pro snocross racer Luke Stephens and Keith Hutchins, AKA “Peanut,” we identified some of the internal parts we were going to use. Working closely with Fox Factory engineers, we changed other necessary parts internally until, through testing, we felt confident that this shock met all of our needs. The end results proved to be so successful that Fox has migrated into a second generation Float, simply called Float2. To continue to address the extra volume air chamber, a new shock was designed specifically for mountain riders and is called the Float Evol R ski shock. This shock has all the same components as the Float2, including a higher rate negative spring, new valving, new valving shims and a high flow piston design internally, as well as a dual stage air chamber and external 22-click rebound adjustment.
With this shock we feel that we have successfully addressed all the above issues. Now you can remove the stabilizer bar with no ill handling effects on the hill or trail. It offers so much more, whether hillclimbing, boondocking or high speed trail riding, that you will be hard pressed to find a better value for your investment.
With the front ski shock successfully addressed, let’s tackle the rear suspension.
The front track or center shock has presented us with its own share of issues. For years our company has offered our customers lighter spring rates to reduce the amount of ski lift. Using the formula for measuring the dual rate springs that we have used in the front track of the Summits, including the Rev and XP chassis, (Spring 1 x Spring 2) divided by (Spring 1 plus Spring 2), we end up with a beginning load of 160 lbs. and a finish load of 320 lbs.
Does Seem Logical
Snocross racers use straight rate springs between 150 and 200 lbs. Now, I realize it is a different suspension design so there should be some differences, but it just doesn’t seem logical to have that much difference, especially considering the abuse most snocross racers impose on their snowmobile suspensions. Couple that with the general information that the front track has a significant influence on handling and it seems like the best option in our opinion is to offer our customers a slightly lighter spring rate in unison with a Fox Zero Pro Shock that has a slightly higher compression valve rate than a factory stock shock.
For customers who still want the dual rate spring combination we end up with approximately 25 lbs. off the beginning and 100 lbs. off the end or finish load of the stock springs. If the dual rate is not critical for the rider we offer 150- to 160-pound straight rate springs and Fox Zero Pros. For either spring rate combination, we recommend installation of a lighter rate spring as well as the Fox Zero Pro. The end result has given us a better handling sled and a smoother ride. On any sleds we sell or work on we make the customer aware of this information, and based on his decisions, we adjust his front track system.
On the rear track, unless the rider is 160 lbs. or less, we typically always offer or recommend a stiffer rate torsion spring. We have the Fox Zero Pro shock valved to address the stiffer torsion rate so it is compliant with the increase in spring pressure.
In addressing the rear suspension, front and rear is always discussed as a package. We prefer not to put the lighter front track springs on if we do not install the heavier rate torsion springs as well as the Fox Zero Pros. We will install rear suspension springs only if the customer’s budget has reached its limit or he is not interested in the Fox product. Our preference though, is to offer a complete package that includes springs and Fox shocks.
Both rear suspension stock shocks can be revalved, in addition to any of the above combinations, to address rider preferences as well. Typically you would do this for the rear track shock if your rider weight were higher or lower than the average or normal weight or you were an extreme jumper or you simply wanted a smoother ride on the trails or in the trees.
There are a lot of options on the rear suspension to accommodate just about any rider or preference and we have made it our business to listen to our customers so that we can offer the best solution for any given situation. We consistently use rider feedback to monitor our suspension packages as well as continue to test or push the limits as much as we can through various different avenues including racing. With this desire or passion for improving what we ride, we consciously push ourselves to learn and improve on existing technology.
That brings us to the last part of our rear suspension. One of our criteria for the rear skid was that it needed to be coupled, similar to the factory suspensions. In working with the air shock up front on the ski shocks, it became apparent that there were some obvious advantages to using air for the rear as well. These advantages include lighter weight and more rider adjustability, as well as a reduction of trapped snow in the rear skid or snow flow.
Starting with the front track shock, Fox built a prototype replacement Float air shock. With the new air shock, we found that our air pressures could be as low as 45 lbs. of main chamber air pressure. This would be equivalent to approximately an 85- to 155-pound spring rate. By simply adjusting this air pressure, say up to a maximum of 65 lbs., we could get the spring rate to change to approximately 120-195 lbs. These pressures definitely fell within the range of what we were working with on standard and dual rate springs and continued to allow for easier ski turn in the front. The other benefit was our excessive ski lift was even less than with our lighter weight springs in the stock setups. This allowed even more rider-controlled weight transfer.
The rear track shock, once repositioned to accommodate the Float body, also offered more adjustability with the air chamber adjustments. Looking to further improve the rear, we decided to build a second rebound-adjust Evol shock to make our spring rates a little more linear, as well as offer more bottom-out resistance with the extra pressure from the Evol chamber. In essence, it gave us a dual rate spring rate design. To counter the higher air chamber pressures you have an external 22-click rebound adjustment. This design allows a wider range of spring rate adjustment for customers to specifically fine tune their desired spring rate, based on their riding style, weight and other modifications that may have been done to the sled.
The combination of the actual dynamics of the new shocks and the geometric changes to shock position or mounting point offered significant improvement of the ride quality. Though the rear shock angle change was minor, it altered the projective motion of the entire rear suspension, resulting in better merging of horizontal and vertical travel, resulting in a better range and rate of motion with speed and force, delivering a very smooth suspension, capable of gravity-defying suspension travel.
In head to head comparisons with some of the best stock suspension changes we had installed, as well as utilizing the Fox Zero Pros, we could not come close to the comfort or control of the sled that we experienced on our new evolution air rear skid and newly-designed front ski Fox Evol Rs.
Plain and simple, it just was not a fair comparison. Our ongoing effort to improve our sleds’ suspensions is really what our objective or target was in the first place. With this new approach to suspension design we feel that we addressed this and are just beginning to scratch the suspension tuning surface.
In the prototype stage of our ongoing testing and design of rear shocks, we will be able to offer an Evol X rear shock that should offer the customer close to 1,000 external adjustments. That should accommodate any rider preference with simple rider available adjustments.
Our weight loss from the suspension, with torsion springs, front track springs removed, as well as inside idler wheels, amounted to an overall weight loss of 9 lbs. from our Ski-Doo Summit snowmobile.
I believe what is critical to a suspension is that each individual rider has options to adjust his snowmobile to fit or suit his riding style and preference and that it be easy or simple to adjust.
(ED—Dines owns Tom’s Snowmobile & Service 530-862-1128 or www.tomssnowmobile.com. Even though he’s the author of the article he wanted to thank a host of others for their help in the suspension work. In his words, “I would like to thank God for life’s journey. I want to thank the engineers at Ski-Doo for doing such a good job on the XP and tackling the weight issue head on as well as the engineers at Fox who have offered ideas, prototype shocks, parts and design and function input. On a more personal level, I would like to thank Gil Driscoll, a retired engineer who, with relative ease and quickness, was able to decipher, locate and weld brackets that allowed us to test rear suspensions in a whole new direction. I would also like to thank Richard Lucchesi and Gary Cudworth for their rider feedback and testing, Casey Gregory for his computer wizardry and understanding of websites, as well as interpreting my sometimes jumbled use of the English language; my daughter Tara, a high school graduate, who helped me understand geometric formulas and equations that sometimes looked more like a foreign language than math.”)
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