FLOATing on Air

"Dear Ralph" January 4, 2016 0
     Dear Ralph: Maybe you can help explain something that has been escaping me and most of the guys I ride with. Reading...

     Dear Ralph:
Maybe you can help explain something that has been escaping me and most of the guys I ride with. Reading the advertisements and most of the other magazines, they all seem to make one think the Fox FLOAT shocks are the greatest thing since sliced bread, but on the sleds I have owned and those my riding buds have bought, we are not exactly impressed. What is all of the hype about, or why does everyone push them so hard? What are we missing?
Confusion in Kohler

     Do not despair, you are not alone. Many riders ask a similar question when they go from a sled fitted with coil-over springs to a sled fitted with a FLOAT. These shocks have been around now for what, 12 years, as they were first introduced for the 2004 model year on some Firecat models if I remember correctly. At least that was the first sled we had them on.

      Regular shocks with a metal coil spring have what is called a straight rate spring. It takes the same amount of force (in pounds of pressure) to compress the spring. If say it has a 90 pound spring rate, it takes 90 pounds to compress that spring one inch, and 90 more pounds to compress it each and every inch through the shock’s travel. And, those metal coil springs are big and heavy.

      Now comes along the FLOAT. Inside it is the same internal floating piston gas-charged shock absorber, but instead of having a metal coil spring it adds a second chamber, or air sleeve, around the traditional shock. This is many riders get confused, as they somehow think the shock itself is an “air shock”. It is not. The shock function is the same gas-charged oil that a piston on the end of the shock rod is traveling through. The “air” portion is the air sleeve around the shock body where pressurized air (inside the air sleeve) acts as an infinitely adjustable air spring. Instead of providing a straight rate spring function, it instead provides a progressive spring rate. The rising rate air spring allows for bottomless feel as the spring rate increases through the travel.

      So on your sled, getting rid of the metal coil springs amounts to about a six pound weight reduction (three pounds per shock) which is really a big deal hanging out there on the suspension. This alone is reason enough to make the switch. Then we have the benefit of the rising spring rate, which comes into play at full travel situations. When you hit a good sized bump, one that would cause the coil spring set-up to bottom out, the rising spring rate of the FLOAT is going to do a far better job at absorbing that bump force and energy and resist bottoming.


      Check out the force vs. displacement graph I found that demonstrates this relationship, or difference between the metal coil spring and an air spring. At full travel, it is going to take a whole lot more force to get that shock to compress all of the way, thus much reduced bottoming.

      Now to answer your question, why do you notice what you do when you switch from a sled with coil springs to one with an air spring. Most riders will comment on how the air spring feels firmer, or stiffer. They continue to comment on this even after they have adjusted the air pressure of the air spring. The first and most obvious is that the hydraulic portion of the shock (remember, piston stack traveling through oil) is not the same calibration between the two shocks. With the added capability of the air spring, the internal valving has also been ramped up to take advantage of the added capabilities of the air spring. This means the air spring shock is generally going to be better suited for more aggressive riders and bigger bump conditions, simply because the base valving is calibrated that way to take advantage of the air spring capability.

      This not always the case, though. Perhaps the best example of this would be with the Ski-Doo Air Ride rear suspension. In that application an air shock is fitted into an rMotion rear suspension that also has traditional torsion springs. The ride quality is impeccable, and the air spring is in there for remote adjustability but also for the added resistance to bottoming. The rMotion is already outstanding at ride quality and being able to be compliant through little bumps with big bump capability, but the addition of the air spring just expands that capability.

      One of the tricks to making a FLOAT shock more compliant is to increase the air volume. Few people know this, but you can have an extra air chamber added to your FLOAT and it will re-shape the spring rate more to your liking, AND in some cases you can get even more adjustability. There are several speed shops that offer this kind of modification at a reasonable expense. One option is to send your FLOAT shocks into a FOX rebuild center and have the new hardware added on at the same time as the shocks are rebuilt. Most shocks should be rebuilt somewhere at the 100-200 hours of use timeframe, which for most riders will be in the 3,000-5,000 mile range. They will basically add the EVOL chambers to your FLOAT shocks and perform the rebuild for $350 per set, which is a great deal. The rebuild service alone would be $120 so in effect you are getting the EVOL chambers for $230 more, a sweet deal when we look at it that way.

      Going to the EVOL set-up effectively gives us twin air chambers that allow for individually tuned and adjusted optimized settings. The main air chamber controls the sled’s ride height, where the added EVOL air chamber is set for the bottom-out & roll control. Having two separate chambers gives you even greater capability to get the shocks to perform more to your liking. The FOX Factory Service Center is in Baxter, Minnesota (Brainerd) and they can quickly get your shocks rebuilt and add EVOL chambers, as well as tweak the internal valving to better suit you as well.

From the September 2015 issue of SnowTech Magazine.

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