Tech Speak: Talking Fork Seals and Lubrication with SRAM and Enduro Bearings
Suspension forks have come a long way since the early days of elastomers. What started as low tech springs attached to the front of our bikes has evolved into extremely sophisticated suspension systems with damping circuits that rival many higher horsepower pursuits. With every major improvement to the suspension fork, one thing has remained mostly unchanged – the lowly fork seal. Often neglected when it comes time for maintenance, the fork seal can have a big impact on how your suspension fork performs.
Winter time in the US means it’s a good time for some preventative maintenance to get your bike ready for the Spring. We were hoping to learn a little more about the ins and outs of suspension seals and lubrication, so we spoke with both SRAM and Enduro Bearings (they make the blue fork seals) to get the scoop from a large fork manufacturer (who has made one of the smoothest forks we’ve tried, more soon on the Pike) as well as an aftermarket seal maker.
Slide past the break for the story.
Bikerumor: First off, what is the main purpose of a fork (or shock) dust wiper or seal
SRAM/RockShox: Dust wipers and seals are used to isolate material to either the inside or the outside of the suspension.
Enduro (Chris Streeter from Real World Cycling): The purpose of a dust wiper is to keep debris out of a fork or shock. The purpose of a seal is to retain lubricant within a fork or shock.
Bikerumor: There has been a lot of talk about the difference between a dust wiper and a seal. Do you consider your design seals or dust wipers? Is there a difference?
SRAM/RockShox: The common vernacular within the bicycle industry is to call both “seals”, which is correct. A dust wiper is a very specific type of seal designed to keep foreign objects from entering the suspension. Some dust wiper designs incorporate internal sealing properties to keep oil and air inside the fork as well. A “seal” is anything designed to contain an object in its space. In RockShox product we have both dust wipers and seals in numerous applications. In Vivid there is a blue dust wiper that you can see and below that there is a seal that holds all the oil in the shock. On forks we use a combination of technologies depending on the application. In most cases we have a dust wiper with internal seals. In BoXXer, Lyrik and Totem we use both a pressure seal and a dust wiper.
Enduro: This is a point of confusion. It is not a case of either or. EVERY semi-bath or open bath suspension fork requires both a seal and a wiper. The point of confusion arises because some companies use a COMBINATION single-piece unit and call it a “dust wiper.” Actually, such a single piece unit is properly called a “wiper/seal,” because it has a seal element at the bottom and a wiper element at the top. The Enduro approach is to have a dedicated oil seal and a dedicated wiper. This allows independent tweaking and improvements in material for each separate component. They don’t do the same job, so don’t necessarily benefit from the same materials.
Bikerumor: Along those lines, for some forks seeing oil wick out of the seals is ok, on others it’s not. What is the theory behind the two schools of thought?
SRAM/RockShox: Visual oil wicking out of dust wipers usually means that the wiper has contamination between the wiper and upper tube. There always is oil on the upper tubes but should not be visible running down the casting. The one exception to this rule is right after a rebuild. The first few rides after a rebuild there will be some additional residual oil and grease that will expose itself.
Enduro: It’s never OK for a fork seal to allow lubricant to leak out. It affects fluid levels and attracts contaminants. If you look into this, you will find that the major fork manufacturer who used to say “they are supposed to leak for lubrication” has now changed their seals AND their position as to whether or their seals are “supposed to leak.”
Bikerumor: How do you balance the tradeoff between stiction and the tightest seal?
SRAM/RockShox: We strive for the lowest friction possible while passing all of testing requirements for debris exclusion and seal longevity. We are constantly improving by developing new seal materials, geometries and test procedures.
Enduro: That’s the big question. Lubricant must be retained with the least possible amount of drag imparted to the system. It requires a combination of angles, proper tension on the sealing lip, materials, etc.. It’s far from over.
Bikerumor: How are your seals constructed? Do you use a foam ring and why?
SRAM/RockShox: Generally speaking seals are molded over steel rings and in some cases have springs added around sealing lips to increase the lip pressure. RockShox uses a foam ring to keep a film of oil on the upper tube before it passes through the wiper to reduce friction and as a secondary trap for any foreign material that might have made is way past the dust wiper.
Enduro: Foam rings have been used based on two schools of thought. As far as I know, RockShox used them first. They placed the foam ring between the oil seal and the wiper. The stated purpose of the foam ring was to keep the wiper lubricated for less stiction. The foam ring would eventually dry up and it was necessary to pry up the wiper and re-lube the foam ring. If not re-lubed, the dry foam would actually impede performance. For this reason, and because prying out the wipers can be a hassle, we don’t include foam rings with our RockShox kits. If your wipers need a bit of lubrication, a better method is to use Finish Line Stanchion Lube, which can be applied from the outside of the fork and does not attract dust the way fork fluid does.
Fox also uses foam rings, but for a different stated purpose. Fox’s idea is that a foam ring UNDERNEATH the oil seal can help retain fork fluid up near the bushings. Our feeling on this is that “it can’t hurt,” so why not respect Fox’s position on this? For this reason, we include foam rings with the Fox kits.
Bikerumor: What is the proper service interval for your seals?
SRAM/RockShox: Dust wiper service should be performed every fifty hours of riding to remain at an optimal performance level. Our professional riders get their suspension seals cleaned in much shorter intervals to make sure their suspension is working at it’s best at all times. A World Cup downhill racer may only do 15 runs between fork seal cleanings.
Enduro: There is no set service interval due to a wide range of riding styles and riding environments. Generally speaking, if one keeps the stanchion tubes clean and no oil is appearing on the stanchion tubes, the oil is probably in good shape. However, anyone who rides in wet and muddy conditions on a regular basis should perform and internal inspection regularly (perhaps weekly). Then, if everything looks OK inside, one may extend the service interval. As this process is repeated, the intervals may end up quite far apart in some cases. For those who are easy on their equipment and ride in dry environments, a minimum annual internal inspection is recommended.
Bikerumor: Do you need any special tools to perform seal maintenance?
SRAM/RockShox: Special tools required are large downhill or motocross type tire lever (something to pry the seal out of the casting) and RockShox seal press.
Enduro: As with many things, a great deal of improvising is done by those who perform their own fork maintenance. For example, an inverted socket can be used as seal press. While not ideal, it certainly does the job most of the time. However, a proper seal press tool with as pilot will insure the seal goes in straight and with the least amount of force, which ensures that the seal is not damaged during the installation. Having a graduated oil syringe with which to measure and inject fork fluid into the casting holes at the bottom of the lower legs certainly makes the job a lot easier. Also, a spoon-shaped DH tire lever (such as that made by Pedro’s) allows the seals to pried out with very little likelihood of damaging the inner surface of the seal head. Certain forks have fixing nuts that are deeply recessed and require either a special socket from the fork manufacturer, or perhaps some custom grinding of a standard socket performed by the mechanic.
Bikerumor: I know a lot of people that try to eke out a little bit more performance out of their seals by trying to squeeze in lubricant between full services. There are even products out there now specifically designed for that like Finish Line Max Suspension spray. Are these methods effective, advisable?
SRAM/RockShox: It is a good idea to clean your upper tubes and seals externally before each ride. Adding a little lube to the outside of the seals, then pushing on the suspension can help lift a little more dirt out from the seal. Wipe off the excess and head out for your ride. We definitely do not recommend using anything to pry the seal lip away from the sealing surface and trying to dig out any debris. If you have that much contamination, it is best to pull the suspension apart to clean so you don’t risk damaging the seals or sealing parts.
Enduro: Some fork and seal combinations benefit from lubrication of the stanchion tubes. Others really don’t seem to need it. In large measure, this depends upon the coatings used on the stanchion tubes. Conventional wisdom would say that the smoother the coating, the less stiction. Conventional wisdom would be wrong. A highly polished very closed pore surface has no place to hold lubrication and often can be rather sticky. In addition, on a microscopic level, it also means more surface contact between the stanchion tube and the wiper and seal surfaces. In this case, Finish Line Stanchion Lube applied periodically can be helpful.
Bikerumor: What is the easiest and most beneficial way to keep your suspension working properly?
SRAM/RockShox: Keeping the suspension clean before and after each ride and following manufacturer’s service intervals.
Enduro: Use good quality seals and lubricants, keep the stanchion tubes clean, and invert the fork just before riding to pre-lube the bushings.
Bikerumor: Does the quality of the coating/smoothness on the stanchion have anything to do with the seal’s effectiveness?
SRAM/RockShox: Quality and smoothness are not synonymous in the world of surface finishes. For example if you had a perfectly smooth upper tube, it would lack the ability to hold any lubrication as it moves in and out of the seal. This would result in the seal friction being insanely high and in many cases result in premature seal wear. Because of this, the seal and the surface finish need to be designed and tested together to ensure in a variety of conditions they preform as intended. Just changing the surface finish does not mean you will get an increase in sealing performance. For example the BlackGold upper tube finish we used in BlackBox had less friction than our standard anodized upper-tube, but preformed the same in terms of sealing.
Enduro: As previously mentioned, A highly polished very closed pore surface has no place to hold lubrication and often can be rather sticky. In addition, on a microscopic level, it also means more surface contact between the stanchion tube and the wiper and seal surfaces. However, to the naked eye, a stanchion coating that looks very smooth may, in fact, have a relatively rough surface when under a microscope. If these irregularities are not large enough to allow fluid to leak, but do allow enough to penetrate the surface and provide lubrication, the result will be less stiction. Surface coating materials for optimum performance is a science of its own.
Bikerumor: How do you lubricate the internals of the shock – is it open bath, closed bath, grease, etc?
SRAM/RockShox: All RockShox must use RockShox service kits and RockShox suspension oil only. The reason for this is that seal materials react differently to different lubrications, sometimes resulting in seal swelling or shrinking. At RockShox we specifically design and test the compatibility of our sealing materials with the lubricants we use. We have seen many cases where other lubricants are used and the seals shrink resulting in leaking.
Enduro: We make aftermarket seals for forks and shocks. We do not currently have a line of forks or shocks of our own.
Bikerumor: Do you use a special grease for your bushings?
SRAM/RockShox: RockShox bushings are lubed with the oil bath in the casting, we do not recommend the use of grease on our bushings.
Enduro:Most forks on the market today are open bath or semi-bath, meaning the bushings are lubricated by fork fluid. I am aware of one brand that has gone back to grease lubing, but, in my opinion, it is only due to a failure to produce a satisfactory oil seal for their product. Grease lubed forks went away for a reason.