How To Adjust
SHOWA SFF Fork Preload

SHOWA forks have long been an excellent choice for motorcycle suspension, and recently SHOWA introduced the SHOWA SFF (Separate Function Fork) which makes more exact tuning of the front suspension on the 2011, 2012 & 2013 Kawasaki KX250F (and for 2013, the Suzuki RMZ250 & RMZ450's) a whole lot easier than previous models as the SHOWA SFF fork allows external adjustment of the front suspension's spring preload and resultant sag through the use of the external preload adjuster located at the top of the right fork leg.

Although the idea of separating the damping functions in a fork is nothing new as Marzocchi had implemented this design in 1993 with their conventional style 45mm "Magnum" forks.

Similarly to the previous Zoke's, (although greatly advanced in valving technology) the Showa SFF fork houses the damping in one leg, while the other houses the main spring, hence the name Separate Function Fork (S.F.F).

We're not here to provide any test data or opinions of the SFF over other dual chamber style forks but we can say there are obvious benefits to this fork over previous models from it's simplicity, to the fact that the SHOWA SFF setup is approximately 1.5 Lbs lighter than previous model forks which is achieved with only one leg handling the damping, while the other is responsible for housing the spring.

The left leg of a SHOWA SFF is essentially nothing more than a Twin Chamber fork (minus a spring) where you'd normally find an external low speed compression damping adjuster at the top of the left fork leg, with a low speed rebound adjuster positioned at the bottom of the LH fork leg in just the same manner as previous versions of the SHOWA TC (Twin Chamber) fork.

Considering external adjustments and tunability of a fork leg, there's not much difference between the left leg of a SHOWA SFF and a previous Twin Chamber fork.

Anytime you're measuring or adjusting the sag it's best to get both the front and rear balanced together (yes, the amount the front fork's sag under weight is adjustable) although with conventional, cartridge or twin chamber forks, adjusting the front sag was never possible without disassembling the forks to add washers or spacers under the spring so as to affect the fork preload. Needless to say, for most amateur racers or riders, adjusting the front sag is something that rarely, if ever got messed with.

Picture of the Preload Adjuster on a Kawasaki KX250F

With the SHOWA SFF, external adjustments to the forks are no longer limited to compression damping, rebound damping and fork height, now the fork's spring preload, ride height and sag can be fine tuned via the external preload adjuster located on the top of the RH fork leg.

It's important when tuning the forks, before any adjustments are made, be sure that the air is bled from BOTH fork legs, otherwise accumulated air pressure may cause unpredictable results in your tuning efforts.

How To Measure and Adjust the Fork Preload

  1. Begin by placing the bike on a stand while ensuring the front wheel isn't in contact with the ground.
  2. If you haven't already done so, bleed the forks of any accumulated air pressure.
  3. Now measure the distance from the bottom unsprung portion of either fork leg (The bottom edge of the fork guard works well) to the wear ring on the fork slider (looks like an external snap ring) and note this measurement on one of our free motorcycle setup logs.
  4. Next take the motorcycle off of the stand and bounce the suspension as suggested in the article on adjusting and setting the sag, which, if you haven't seen this previously should be a must see before continuing.
  5. After the suspension has been bounced as discussed in the article on measuring and adjusting the rider sag, take a second measurement from the same points as above with the motorcycle on level ground while under the riders weight.
  6. With the two measurements noted on your basic setup log, subtract the second measurement from the first and this will be the rider sag.

The amount the front of the bike sags under weight or dives under braking is adjustable through the use of replacement spring(s) and / or preload adjustments although to add or remove spring preload in most forks, doing so requires disassembly of the forks so as to enable placement of washers, shims and spacers under the fork springs.

Fortunately on a SHOWA SFF, the spring preload is externally adjustable (to a point, at which point a replacement spring will be necessary to maintain the proper balance).

Remember When Adjusting the SFF Spring Preload

6 Clicks of the Preload Adjuster Removes or Adds
Roughly 1mm (~.040" or 1/16") of Spring Preload
Image of SHOWA SFF Preload Adjuster and Air Bleed Screw
  • To reduce or increase the amount the front of the bike sags under the riders weight, begin by cranking in, or removing spring preload via the blue or gold colored adjuster at the top of the RH fork leg.

Don't Forget that 6 clicks of the knob equates to 1mm of PRELOAD, NOT actual sag.

  • Once a preload adjustment has been made, roll the bike again while bouncing the suspension as mentioned in our article on setting the front and rear sag, then allow the suspension to come to an easy rest with the rider aboard.
  • With the rider aboard now take another measurement in the same manner and from the same points as used in your initial measurements and adjust accordingly, continuing this process until an ideal fork sag is achieved and the bike handles predictably.

As with any adjustment of the motorcycle in a quest for better performance, it's important to constantly test different setups from tracks or riding spots, although once an ideal ride height setting is achieved, and the motorcycle feels well balanced & mannered, measure the compressed distance again and record this in one of our basic setup logs, this way you can refer to this for later reference when returning to a specific track or riding spot.

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