How do I know which "+ size" head to use?

This will depend on how the fork feels. The stickier the fork feels and the less willing it is to move, the larger the +size required. If your fork is rebuilt with fresh fluids and feels good, but partway through the first ride or in the next few rides the fork starts feeling sticky and harsh, then its a good indicator that the +.10mm head or larger would be required. If your fork generally feels ok, but not fantastic and doesn't degrade super quickly after a service then the +.07mm head will likely be just fine. If you've burnished your fork and it still feels like there is stiction and excess friction and harshness while riding then you may need to burnish with a larger +size. Forks with oil channels behind the bushings are more common for needing larger +sizes to remove the out of round it creates.


What is the right diameter that my bushings should be at when I am done burnishing?

The most common and familiar bushing size specification originates on the Fox website and it lists acceptable diametrical bushing clearance from .0015"-.009" (.038mm - .229mm). Other manufactures have their own specifications and tolerances around the range of acceptable bushing clearance. Just because a bushing is within specification for clearance doesn't mean it is ideal. A .038mm clearance is too small to provide space for a good oil film and accommodate flex of the fork to provide low friction. Conversely .229mm is much too large and will create excessive knocking of the bushings and put excessive wear on the internals of the fork causing premature failure. All +sizes of our burnishing heads will result in the bushings ending up within the ideal range of clearance  at ~.05mm to .09mm-.10mm (.002"-.004") for proper formation of oil film between the bushing and stanchion without excessive clearance. Most forks will respond wonderfully to the +.10mm size, it is less common to need the larger +sizes to get forks feeling good. 37mm dorados more commonly need larger sizes such as +.13mm and +.18mm (available soon).


If I burnish my fork with a +.07mm head or a +.10mm head will that be the new diameter of the bushing when I am done?

No, there is spring-back in the bushings so after the tool passes through, it shrinks back down. The larger the tool passed through the bushing the more the spring back, so the relationship between burnishing head size and resulting bushing diameter is not linear.


If I use a head larger than +.10mm, say +.13mm or +.16mm won't the bushing end up larger than +.10mm in diameter even after accounting for spring back of the bushing and result in excessive play?

No, the final diameter of the bushing depends on how tight the bushing felt before starting to burnish. We have run tests on multiple forks and bushings that worked individual bushings for 2 hours each with a very large +size head and found there was still resistance passing a +.10mm head through afterwards, the spring-back becomes exponentially larger with a larger burnishing head, but the results in terms of friction reduction from burnishing with very large +sizes are incredible. It should be noted that to go larger than +.10mm it is first recommended to use a +.10mm head before going to a larger size. Some forks can have extremely tight bushings and it can be very difficult to get the heads larger than +.10mm through the bushings without working a step before.


Why don't I just use the largest head possible for the most friction reduction?

We are big fans of keeping forks feeling as tight as possible, so its recommended to not use the absolute largest +size all the time if it isn't required. +.10mm is a great size that the majority of sticky forks will see a great benefit from. +.13mm and larger will make further benefits if the fork is still sticky after using a +.10mm size but in most cases the +.10mm gets the fork about perfect and leaves little for larger +sizes to do. Many times forks can have very tight feeling bushings when using the burnishing tool so sizes larger than +.10mm require that a +.10mm be run through the bushings first to allow usage of the larger +size.


How do I know how long to work with the burnishing tool? Can I go too far with it?

No, you cannot over-burnish with our tool, you could spend an hour working each bushing and still not go too far with our tool (this goes for every  "+size"). As the tool is passed back and forth through the bushings, the resistance to push the tool through will decrease and eventually the resistance will stop decreasing and the force required will become constant, this is the point of completion. Sometimes the lower or upper bushings may feel like they have different resistance, as long as the resistance is approximately the same for all bushings, then that is all that is required. Sometimes the upper and lower bushings may be looser or tighter than each other, but if they are the same side to side (ie. both lower bushes feel the same but are looser feeling than the upper bushes, and both upper bushes feel about the same) then that is perfectly ok too.


I don't want any noticeable play from the bushings in my fork at all, how can I keep bushing play at precisely zero?

There is a lot of misinformation regarding bushing play and it focuses on any play in the bushings being bad. This is mostly felt during parking lot tests. There is a tradeoff between bushing clearance and friction. Larger bushing clearances allow less friction but more feelable play in the fork. Lower clearances make less feelable play but can lead to a harsh feeling fork from excess friction. Zero clearance and resulting zero bushing play would mean the fork would struggle to move and would ride like a rigid fork. There needs to be a minimum amount of clearance for the fork to work properly and it will result in a small amount of feel-able play but it should not be an excessive amount of feelable play where the fork bushings actually clunk on the stanchions. The right amount of clearance and bushing play associated with it will not be feelable during riding and should be barely feelable in parking lot tests. Parking lot tests often expose brake pad clearance in the caliper and loose headset issues which is commonly mistaken for fork bushing play. A great example of too much bushing clearance is Marzocchi forks from 2008-2009 after manufacturing moved to Taiwan from Italy. These forks were constantly being sent for warranty for excessive bushing play because they "knocked" badly, but the large clearance meant they were incredibly smooth. An example of a fork with too little bushing clearance is the new generation 37mm Manitou Dorado. The 36mm chassis dorado had appropriate bushing clearance so as not to have excessive bushing play, but also not be too tight, those forks rode wonderfully smooth. The 37mm Dorado bushing clearance has been tightened right up to provide extra torsional rigidity to the fork, but on many of them the bushings are too tight and cause excess friction, stiction, and a harsh feeling fork. 


Do I need to use a different oil for burnishing or a different lower leg oil after I burnish the fork?

Use the oil specified by the manufacture for your fork. Pro tip - thicker oils will mask clearance in the bushings better than thinner oils.


We are always available to answer questions by email at info@rmsuspension.com