Thank you for purchasing a Spring Conversion Kit. This kit converts the stock air spring forks to a coil spring. You will notice improvement in ride quality as well as eliminating both the possibility of a blowout and the hassle of maintaining the air.

These instructions cover the Showa TAC and Inner TAC designs. The TAC Forks have an external chamber as in the picture below.

These are SFF (Single Function Forks) which means the damping is in one leg while the other leg has the air spring force. Only the air spring leg needs to be worked on to install this kit.

Springs - Sold separately. In general 49mm forks require FRSP 4566 Series Springs. 48mm forks require FRSP 4466 Series Springs. 

To get the ultimate performance we, of course, recommend Compression and Rebound Gold Valves and Ultra Slick Oil.

Installing this kit does not require splitting the Fork Tubes. If you need to replace Seals or Bushings click here for general Fork rebuild procedures. 

USF-05 Fork Oil - extremely slippery
Contact Cleaner - or other good, clean solvent
Fork Springs (check the Product Search for rate recommendations)

 Tools Required
- TFCW 4650 - Fork Cap Wrench
- TFCT 3602 - Fork Cap Tool
TMVJ 065 Vise Jaws mounted on a Vise - suggested
- TFGC 500 - Graduated Cylider


1- Hold the Outer Fork Tube in the "V" of the TMVJ 065 Vise Jaws at the point where the Lower Triple Clamp contacts the Tube.

2- Depressurize all air chambers.
Use the TFCW Fork Cap Wrench to remove the Cap.
Pour out the old oil and dispose of it properly.


3- Use TFCT 3602 Fork Cap Tool to remove the Bottom Bolt. Do not use an impact!


4- Hold the Jam Nut with a wrench and remove the Bottom Bolt from the Rod.


5- Slide out the stock Cartridge from the top.
Clean everything or, at minimum, drain the oil.
Note - If you are switching to Ultra Slick Oil the more old oil you remove, the less contaminated the new oil will be and the slipperier it will be.


Insert a Spring Preload Washer into the bottom of the Fork Tube.
Do not put the Spring directly on the Fork Bottom or it will chip off pieces of aluminum into the oil and damage the forks.
(What happened to that index finger? Fighting Great Whites off the coast of Australia again?)


7- Visually inspect to see that the Washer is lying flat. Use a flashlight if you can't see it clearly. If it is not located properly reach in from the bottom and move it into place.
What do you see in there Paul?


8- Insert the Fork Spring.


9- Install the Spring Conversion Cartridge far enough so it...


10- sticks out through the bottom. Make sure the Jam nut is on all the way. Install the new Bottom Bolt all the way.


11- The Bottom Bolt on the left is for forks with the External TAC Chamber - 2015 KX450F and RMZ450
The Bolt on the right is for the Forks with the Internal TAC - 2105 CRF250.


12- Tighten the Jam Nut.


13- Install the Bottom Bolt.


With the:
Outer Fork Tube fully collapsed,
Spring all the way in,
Preload Adjusting Nut loose, and the
Cartridge extended
measure the reference distance from the top of the Outer Fork Tube to the end of the Spring Retainer.
This is L1. As you can see this one is about 67mm.


15- Tighten the Preload Adjusting Nut to add Preload.


16- Measure the reference distance again. This is L2. In this case it is 53mm.
The difference between L1 and L2 is the Preload.
         67  L1
        -63  L2
           4 mm Preload
Tighten the Preload Adjusting Nut to achieve 3 to 5mm of Preload.
Once you have achieved the desired Preload be sure to tighten the Preload Adjuster Jam Nut.


17- Use the Graduated Cylinder and install the proper amount of Fork Fluid. No bleeding necessary.
USF-05 is preferred as it is impressively slippery (if I do say so myself).
Use USF-05:
525cc for motocross
575cc for SX
500cc for off road
in this leg only.
See DVS or Product Search for Damping Rod leg level.


18- Tighten the Fork Cap.
Improper fork installation is, perhaps, the most common error that is made. This has a huge effect on harshness!
Have fun!