Cartridge Emulator Installation

The goal of this 2004/2005 winter project was to improve the Concours front forks compression damping, without changing any other front suspension variables. The emphasis is on comfort rather than racer road holding. So, the plan was to install RaceTech FEGV-S3801 Cartridge Emulators, shorten the stock springs by the 14mm height of the emulators, and retain the same oil volume and viscosity.

Some measurements of the stock springs:
Spring Outer Diameter 30 mm 1.1811 inches
Wire Diameter 5 mm 0.1969"
23 high-pitch coils, 35 low-pitch

Found a Simple Spring Constant Calculator on the web, and the calculated spring rate for the stock 543mm springs was 0.724 kg/mm.

Advice on spring shortening came from Tech: Stiffer Springs For Free! Coil Spring Tuning Secrets by: Rick Sieman and How to make the Yamaha XS11 Handle.

At the high-pitch end, I cut off about 1 1/4 turns by heavily nicking the spring wire with a file, then breaking off with a vice. I then propane-torch heated to bend flat and filed to make flatter. Net result is 529mm long and a bit stiffer than stock (0.737 kg/mm), but providing the same amount of preload. These calculated figures are initial spring rates for these progressive springs, the final spring rate (when all the close-pitch coils are collapsed) is calculated as around 1.7 kg/mm.

This is a post-'93 stock damper rod, with two compression damping holes near the bottom, each about 3/16"" in diameter. It fits into the tapered lower sleeve at the bottom of the fork, which is there to cushion complete compression.

FYI, the top of the damper is broached to fit a 5/8" dia. nut which is 24mm|15/16" across the flats.

So I stuck said nut (with a light coating of masking tape) half way into a 24mm socket, and used it and a bunch of extensions to hold the damper rod while loosening and tightening the bottom bolt.

This is the same damper rod, with the stock holes drilled out to 5/16", and 4 additional 5/16" holes above the stock holes, as recommended by RaceTech.

Because the stock springs are progressive, I used the stock oil quantity (320 CC) rather than the higher oil levels recommended by the straight-wound spring proponents. I also stuck with the stock viscosity recommendation (10W30) so that rebound damping would not be affected. In the interests of comfort, I used 1 1/2 turns of preload on the emulators, rather than RaceTech's recommended 2 turns.


Modifying and retaining the stock springs was frugal.

What I noticed on the initial deliberately-bumpy straight ride is that jarring is now more noticeable at the rear, while before it was harsher at the front. Similarly, in a bumpy turn, the front now seems more firmly planted than the rear. So that means the whole cartridge emulator thing is a success from the comfort viewpoint, but it also means I may have to look at the rear suspension sometime.

And the only substantial change was the addition of emulators.