NSS250 Reflex Fork Tuning

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The forks on the 2005 NSS250 are OK. They don't completely suck like those on the Ruckus, but they do need some tuning.


  • Front Wheel Travel - 100mm (3.9in)
  • Front Axle Travel - 88.7mm (3.49in)
  • Caster Angle - 27.5 degrees
  • Trail Length - 95mm (3.7in)

The Parts

The fork of the Reflex is a classic damper rod type construction. It has no external preload adjustment.



After getting the bike to sag 35mm, the resulting 11mm of free sag is just too small. It should be between 15 and 20 mm, a stiffer spring should be ordered.

The stock spring is 269mm long and 26mm in diameter. I think that the ID is around 20mm (poor measurement).

The spring was a classic dual rate spring, but I didnt rate it. I was in a rush.


I did a basic sag on the bike. Measurement of chrome showing under the clamp and above the dust seal.

  • Unlaiden Length - 105mm
  • Free Lenth - 83mm
  • Sagged Lenth - 59mm

Basically, the bike is sagging 46mm. Typically, a standard motorcycle front end of a modern sport bike should sag 35mm for street riding. At 30% sag for this bike, I should be seeing 33mm. I added an 11mm spacer to raise the bike's ride height. 11mm height x 25.4mm diameter.


  • Fluid - Showa SS-8, ISO 36
  • Height - 63mm
  • Volume - 121cm^3

Stock fluid for this type of fork is Showa SS-8 (ISO 36). Typically a damper rod fork requires a fluid of at least ISO 65 to start marginally working in slow speed.

I changed the oil to Red Line (Heavy), ISO 66.80.

Oil height was kept the same as found at 75mm.

If installing the emulators, Race Tech recomends US2, ISO 32.9. Essentially, any ATF (ISO 34) is a good substitute for this fluid.


I hope to convert the fork to a cartridge type. I have some parts laying around, all I need is the room.

If I cannot, I hope to add a Gold Valve Cartridge Emulator

  • FEGV S3001 FRK EMULATOR-23.8/16.4/13.5mm $169.99
  • FEGV S3301 FRK EMULATOR-26.5/19.5/13.5mm $169.99

I will order S3301 and mod it to fit.

Rt emulators.jpg

The Ride

In stock form, the fork felt spindly. Harsh on bumps and lots of pitching.

After adding 11mm of preload and changing to ISO 66.80 oil, the front end feels much, much better. The forks have a solid, smooth feel. Much better over bike bumps.