SUSPENSION TUNING

IDEAS TO SHAKE UP THE INDUSTRY!! **

by Brad Finkbeiner, published in SnowTech Magazine 1998

** Applies to Brad’s BLT from 1998.  The thoughts and opinions of the author, as well as Brad himself, would like to clearly state that a lot of this no longer applies, as technology, engineering, and design of modern shocks have eliminated a lot of the problems with emulsification and/or emulsion-style shocks. Like all industries, we’ve had to evolve. We’ve come a long way, baby.

Sincerely, Brad

** SUSPENSION TUNING IDEAS TO SHAKE UP THE INDUSTRY!! **

As you’re riding down the trail the section ahead looks rougher than anything you’ve seen all day and your body has just about had enough. As you prepare yourself for the next round of impacts, another machine comes past you – and the guy looks fairly comfortable at that, his machine seemingly gliding through what you thought was the worst section of the day! You’re both on late model sleds, so was he nuts, or did he know something that you didn’t?

Ask just about any snowmobiler which area of the sled has the farthest to go in terms of development, and most of them will tell you that the suspensions are where the biggest advancements remain to be made. Brad Finkbeiner, of Brad’s AC Performance, agrees and hopes to be one of those to lead us down the path of smoother riding and better handling through continued shock & suspension development. Brad is perhaps best known for his wide front-end kits, Works Performance emulsion shocks, and programmable springs.

WIDER IS BETTER

Remember the Pontiac commercials? Everyone knows that “Wider is Better”. Anytime you widen the front end of anything you increase the stability. End of story. If there wasn’t an advantage to a wider front end, there wouldn’t be a 41″ width rule in racing. Widening the front end makes the sled very stable, body roll is decreased, the steering effect is reduced, and riding the machine becomes “easier”.

Brad started to build long travel front ends because he has carpal tunnel syndrome. He had long been one of the “top dogs” in his riding community and really loved being able to ride his big ZRT 800 in the really rough stuff, but the big 800 and Brad’s carpel tunnel made for a deadly combination. His beloved sport was going away from him – fast. His hands hurt so badly they would ache and swell to the point he couldn’t go out and do those 200+ miles days anymore.

Brad started to look for ways to change the “front end feel”. The first thing he did was buy a set of SLP Ultra Lite Skis that claimed to offer “power steering”. They worked so well that Brad realized if the skis could make that much of a difference, what else was there in the front end to improve upon?

Out on the trail, Brad met an old friend who was riding this Thundercat with a wide front end. They started talking about the front end, they talked about Brad’s hands, and then the guy told Brad that he ought to ride the T-Cat. Brad rode it and immediately knew: “This is what I need”. It took a large amount of the chop out of the bumps and allowed Brad to ride the way he wanted to ride. It was easier to steer and was just an unbelievable difference. Brad was so impressed with the potential of what this guy had that they entered into an agreement, allowing Brad to continue to develop and bring the concept to market.

Brad started making wide front-end kits for Arctic Cats, however, he now designs and sells wide front-end kits for all four brands. These kits not only increase the ski center-to-center width out to 44″, but they also increase the travel by using longer shocks. The trick is to increase total travel without increasing the ride height – and Brad’s kits maintain the ride height as close to stock as possible, usually within 1/4″ to 3/4″ after the springs take a set.

Brad is able to increase the travel without raising the ride height by increasing the ride-in, and he feels very strongly about “ride-in” or “ride-sag” on suspensions. Brad says that’s where the control and the feel come from as the shock and the spring enter the zone where they work best. With the proper ride-in the suspension is not tensed-up waiting for a bump to overcome the preload, but relaxed and working all the time. That way, when a “real” bump actually comes along the suspension is already “working” and simply has to move farther, not just start to move and cause chassis disruption. Most stock front suspensions are “tensed up”- measure your front bumper height, then lift the front of the sled off the ground, set it down and re-measure the bumper. No difference? No ride-in. Rider weight has nothing to do with this, its all a matter of pre-load.

Why is a 44″ center-to-center the magic width? Brad tried all kinds of front-end widths from 42″ up to 50″ and says the 48″ is the ragged edge, but 44″ is really the place to be. In their testing, 44″ seems to be the “point (or width) of diminishing returns”. As you increase the width, inch by inch, up to 44″ the handling and ride gets incrementally (but noticeably) better, but past 44″ the improvements aren’t as noticeable. At 44″ the sled becomes very stable and maneuverable, and the machine delivers a whole new way to how you think about riding. Also, by keeping a 44″ center you’re able to keep the overall vehicle width down around 48″ so you can still get a couple of these sleds on a trailer and drive down a trail legally.

How wide is too wide? Brad says that a 50″ wide sled they built was too wide. When you get up to 48″ it becomes obviously wide up front, but it also gets to the point that you get off your sled and just laugh. The sled gets sooo easy to ride and control that it takes the challenge out of it, like “who couldn’t ride this snowmobile?”

This kind of “easy to handle” machine is very attractive to some riders. For bonsai riding in rough conditions, it is very impressive, and the wide front-end kits really work well for those who may be approaching their “senior citizen years” of snowmobiling. These are the riders who want a snowmobile that will allow them to continue to “ride and hang with the younger kids” and not wear themselves out.

** EMULSION SHOCKS VS. INTERNAL FLOATING PISTON SHOCKS **

Gather ten so-called “shock experts” and run this past them and watch the sparks fly. Like clutching, there are plenty of self-proclaimed shock experts. Brad does not claim to be an expert, but he does have some rather unusual methods to produce some impressive results- which requires us to take a close look at what he’s up to.

Getting snowmobilers to change their ways is difficult, and it applies to getting them to change their shocks. Say “emulsion shock” and people get this idea that they’re no good because they’ve been programmed to automatically think the IFP (internal floating piston) high-pressure gas shocks (like Fox, Ohlins, Kayaba, and HPG) are so much better. Are they?

IFP shocks, as their name implies, have a “floating piston” with seals that separate the nitrogen charge from the oil. This has always been stressed as the benefit of the IFP design. People look at emulsion shocks and say “the emulsion shock will fade faster because there’s gas mixed with the oil”.

In Brad’s world of shock tuning, whether you’re mixing the nitrogen with the oil or not really has no effect on how soon the shock will fade. Fade is a result of boiling. And it’s the oil that’s boiling (not the nitrogen) that causes shock fade.

How do you change a boiling point? You raise the pressure, just like putting a radiator cap on. That’s what we’re doing with the high-pressure shocks. The pressure is in effect ” a radiator cap on” and raises the boiling point, making the fluid effective at a higher temperature range to increase its durability and longevity for continued use. Emulsion shocks, just like IFP shocks, can be charged with high pressures of nitrogen so they can have similar resistance to fade. The difference is that IFP shocks use a piston to separate the nitrogen from the oil, emulsion shocks do not.

The problem with the IFP shocks is this: when (not a matter of if, but when, because it happens to all of them) the high-pressure gas charge starts to get past the seals of the piston, the oil becomes emulsified. Emulsion, by definition, means that the oil is gaseous (a fluid mixed with gas ) which theoretically would make the mixture lighter (less density). This in itself is not a problem, except that the shim stacks used for the valving in an IFP shock are very specifically tuned to work with the oil in a non-emulsified condition. When the nitrogen gets past the seals and emulsifies the oil, that valve stack no longer works the way it was designed to.

Guys who have used IFP shocks for years will tell you that when the oil becomes emulsified, the valving is gone. And this condition can happen slowly, or very fast. People commonly get this condition confused with fade- but it is very different. The symptoms may be the same, but the causes are very different. When an IFP shock does become emulsified all at once, it is commonly referred to as being “blown” – meaning that a large amount of the nitrogen has blown past the seal, and the shock no longer works like it is supposed to.

Now, Brad is by no means claiming that IFP shocks are bad. The IFP shock, in a fully charged and perfectly sealed condition, may perform better in racing applications. Their durability is questionable, especially when the high-pressure charge starts to get past the seal. At that point, the advantage is gone. Period. What that tells us is that if you’re going to use an IFP shock, you need the best IFP in the world that does not leak. As soon as it leaks, the shocks go away. If the shock is that sensitive to tuning, is the average customer better off using this type of design? Unless you have the tools, resources, and ability to perform the service, or are willing to buy the absolute best IFP available, Brad thinks not.

This is the long-term advantage of the emulsion shock. Since the valving is designed to work with the oil in an emulsified condition, it doesn’t matter that the gas and oil are mixed – it has to be for the shock to work properly. Once you accept this, the rest is easy. Instead of fighting the separation of gas and oil, let them mix and adjust your valving accordingly to deal with it. This makes the emulsion design better suited for the average consumer, regardless of how hard he rides, because it will perform consistently for an entire season without the fear of “blowing” the shock.

** MYTHS ON SHOCK VALVING **

Which is more important, compression valving or rebound valving? Brad says rebound is more important than compression, but that the shocks need to come with better springs to handle the task of compression loading, and then you use rebound damping to control what happens after you load that spring. Think of “compression damping” as controlling the rate of compressing the spring, and “rebound damping” as controlling the release of the stored energy in the compressed spring.

According to Brad, compression damping is moot. Not worthy of consideration or discussion because it really isn’t that important. You just need some valving in there to make it work. What you do need is to have the right spring, resistance to force, which is why he uses dual rate programmable springs with adjustable crossover points ( the amount of travel at which the spring rate changes from the soft rate to a firmer rate). This is how you get the actual “compression feel” right, then you’ve got to find the rebound.

To get that “final touch” to a shock the actual compression damping is important, but it should be the final step, not the first. When tuners start out chasing compression damping they’re going the wrong way. The first thing you want to establish is the spring rate. If you’re bottoming, you don’t need automatically more compression damping, you need more spring (one that can store more energy) or you need to alter the crossover point of the springs – and then you’ll need better control of the rebound of that energy.

Many tuners can relate to this. As they try to get their sled set up they will add more and more compression damping, only to end up going to a stiffer spring and then backing off the compression damping. We always thought this meant that any large charges in spring rate required large changes in compression damping, but maybe what it was really telling us was that the compression damping change wasn’t doing one whole heck of a lot and that the spring change was what really got us there.

The problem with most suspensions is that a single rate spring is selected to provide “big bump” control, but this ends up being too stiff for small bump comfort. One rate can not do it all and shock builders try to get around this by using valving.

What this boils down to is that we should use the springs to tune the shock, instead of tuning a chock around a spring. This was the major turning point in the development of Brad’s suspension.

TUNING WITH PROGRAMMABLE SPRINGS

The typical Works shock consists of the long main spring, a short second spring, a sliding go-between ring, and the cross-over rings which affect the size of the gap.

As the shock compresses, both springs are working resulting in a relatively soft spring rate, since two springs stacked result in a softer rate than either spring acting alone. As the shock continues to compress, the sliding go between ring contacts the cross-over rings which provide a solid “stop” and “lock-out” the smaller spring. At this point, the short second spring is, in effect, taken out of the process, causing the long main spring to be the only one working. This results in a stiffer spring rate for the rest of the travel.

The system has two major advantages over a progressively wound spring. We can more closely match beginning and final spring rates for individual applications and the cross over point from soft to stiff can be adjusted. The cross over point is controlled by the gap between the sliding go between and the cross over rings. The gap is the amount the short second spring will compress before it gets “locked-out”. A larger gap will cause the rate to stay softer for more of the travel while a smaller gap will cause the rate to be stiffer sooner. The gap is adjusted by installing or removing cross over rings of various thicknesses.

As an example, if we have a long main spring with a 100 pound rate and a short second spring with a 240 pound rate, the initial spring rate will be 71 pounds until the small spring is “locked-out”. At this point we are operating only with the long main spring and its 100 pound rate. This combination will provide a soft (71 pound rate) ride at lower speeds, and then provide a firm (100 pound rate) at higher speeds and we can vary the point that the rate changes from 71 to 100 pounds by changing the size of the gap.

SERVICING SHOCKS

All high-pressure gas shocks that are rebuildable should be rebuilt every year. That means replacing the seals and changing the oil. Why? One reason is due to the “out-migration” of the silicone in the rubber seals. They will, over time, start to dry out, harden, and leak, regardless of use. Another thing that bothered Brad was that when he takes shocks apart he sees marks on the inside and wonders where they’re coming from. What was it being caused by?

You also have something else going on inside of your shock: electrolysis, which is the composition of the components. This is particularly noticed in the shocks that do not have internal plating. When you take the shocks apart, the threads are rusted. If the floating piston is of a different metal than what the bore is, you’ve got electrolysis (as with any contact of dissimilar metals) which means that you have a corrosion that builds up between the seal area and the wall. When that snowmobile sits it has plenty of time for this to happen.

Why should you replace the shock oil every year? Would you drive your truck for two years without changing the oil? No. The oil ends up with contaminants (from the inner workings of the shock), as well as moisture. Ice and water do get past even the finest of seals, and then we get back to the electrolysis issue. The best time to rebuild the shocks is at the end of the season. On Fox shocks, behind the seals, on the seal head, there is corrosion that occurs and this is another reason to get the shocks serviced at the end of the season, not at the beginning. Get the contaminants out before they have time to act.

PROGRAMMABLE SPRINGS

With the programmable springs, Brad is able to control the compression characteristics of the shock. Brad used to have trouble chasing compression issues until he started grasping the potential of what kind of effect the spring combinations and crossover points could have on the compression characteristics of the shock.

Let’s stop for a second. All we have is a piston going up and down in oil. What is so complicated about that? Why does it have to be difficult?

It’s not. The Works Performance shocks use multiple springs to achieve variable spring rates. Anytime you put two or more coil springs on top of each other the result is a new spring rate that is softer than any of the component springs. To put it another way, the softness of the springs adds up. When you look at the springs that are available and the combinations that you can use, you’ll see how you can use the cross-over rings and use them to “lock-out” the shorter of the two springs at different times.

Another advantage to the programmable springs is that if you’re perfectly happy with the gig bump performance of your suspension but the small bump ride is too stiff, you can change the upper spring. Install a softer upper spring which will allow you to make the small bump ride softer but leave the big bump ride exactly the same.

Or, if the small bump ride is fine, the big bump ride is great, but there is a speed in between that it gets pretty stiff, you can increase the gap under the upper spring which will allow the suspension to cross over to the stiffer rate a bit later- giving you the softer ride and the control you were looking for at mid-speed while retaining the beauty of how it worked at low speed and all our before you made the change. You would not believe how effective this adjustment is.. The sled can ride great at low speeds and great all out, but right at 50 mph there is an irritating “jounce” in the handlebars. Remove the thinnest cross over ring and it’s gone.

Some of the manufacturers have been using “multi-rate” springs, which have different diameter coils or variable spacing between coils that provide a similar soft and then firm ride, but they are not programmable. To make any changes (other than pre-load) you have to replace the entire spring. Again, they are primarily tuning the shock around the spring. The Works method allows far greater combinations and allows the tuner to pick and choose their spring rates with greater accuracy, as well as being able to “tune” the crossover point that the rate changes from soft to firm – tuning the springs around the shock.

Ride quality tuning really becomes easy once you get the springs figured out. You pick the long spring for the big bump ride, you pick the short spring for the low-speed ride, then you pick the gap for the mid-speed ride. It’s not that difficult after all, and it seems to work quite well.