On non-cartridge forks, damping (both compression and rebound) is controlled by oil of a certain viscosity passing through little holes in the damper rod (located in the lower fork legs). The smaller rebound hole are near the top of the damping rod and the larger compression holes are at the bottom. The problem with this set up is that you can only change damping by either(i) changing the oil viscosity, or (ii) decreasing or increasing the damping hole sizes. The problem with (i) is that the difference in size between the compression and rebound holes means that any change in oil viscosity will affect each circuit in a different manner. You can "re-valve" your forks as in (ii) by drilling out and/or welding shut some of the damping holes, but that entails some very precise tuning and knowledge (luck?). To make matters worse, since the damping holes are a fixed diameter, they cannot distinguish between high speed damping forces and low-speed damping forces. The best set-up is usually a compromise. See Race Tech owner Paul Thede's 1994 Sport Rider Article
Race Tech Fork Emulators:
Fork Emulators are made by Race Tech and they basically remove the damper rod's compression holes from the game. To install, you must drill out the compression holes on the damping rod to enormous sizes. The result is that, on compression, all fork oil travels unmolested up the damper rod and out the top. Kinda like an oil geyser. The fork emulator is placed on top of
the damping rod (held in place by the fork spring) and regulates the flow of this oil geyser with a pop-off valve (the fork emulator). This valve now serves as your primary compression damping orifice. It is tunable two ways: (i) by spring pre-load, or (ii) by separately purchasing emulator valve
springs with different spring rates. Race Tech claims that oil viscosity has a small/negligible effect on compression damping with the emulators installed. They suggest that you tune your rebound damping with oil viscosity first, then adjust your compression with the emulator.
Fork Spring Issues:
After carefully installing the Race Tech Emulators, I reassembed the forks with a set of Progressive Suspension Fork Springs. Since the emulator acts as a fork spring spacer, it was extremely difficult to install the caps and I found that the static sag on the forks was 0". To measure your sag, see Race Tech owner Paul Thede's 1995 Sport Rider Article. I removed the progressive springs and re-installed the stock Kawasaki springs, but found that they were too soft and I had to dial the emulator up to 5 turns to keep the front end under control. The end result was an overdamped and undersprung front end.
If you own a 94+ EX500 with 37mm forks you can buy the Race Tech Fork Spring kit (straight rate) and begin tuning your front end. Since Race tech doesn't offer a 36 mm spring kit, the solution was to cut the stockers to increase the spring rate. I sent mine to Race Tech and they cut over 1/3 off the entire length of the springs. I then bought a 10' length of PVC tubing in the appropriate diameter and made several spacers in 10 mm increments so I could tune my sag faster and easier.
I might suggest having a professional suspension shop modify the springs simply because they usually have a spring measuring machine which determines the spring rate quite accurately and eliminates guesswork. Race Tech has a chart that has your body + bike weight on the x-axis and the spring rate on the y-axis. There are two curves, one which for sport-street riding and the other for all-out racing. I got mine cut for my weight at a rate just below all-out racing. Race Tech charged approximately $50 plus some shipping and handling. A nice part of their deal is that they grind the cut end smooth, heat it and bend it flat as if it were a stock piece (looks very sano). That helps prevent the jagged edge (if I had to cut it myself) which can be hazardous to some fork internals. They do not suggest cutting the Progressive Springs because it is difficult to measure the spring rate accurately and, in addition, the emulator's action get a bit confused with a variable spring rate.
Damping Issues:
Rebound, unlike compression, is mostly dictated by the release of energy stored by the compressed spring. In my case, the modified springs were making the forks rebound very rapidly, so I experimented with various oil viscosities to slow down the rebound. I ended up using PJ1 30wt fork oil but am still unsatified and feel that I require additional rebound damping. I spoke to a technician at RaceTech and he suggested I disassemble the forks and braze up the rebound holes in the damper rod and re-drill them to a diamater that is one-half the stock size.
I have not taken this step yet, as the 30wt oil is O.K. for now. One problem with using 30wt oil is that the low speed compression orifice on the emulator is ruled by oil viscosity. Before the emulator plate blows off and releases oil, low speed damping occurs by fluid forced through the blow-off plate bleed hole. If very thick fork oil is utilized, this effectively makes low-speed compression damping very stiff. To alieviate this problem, I, with RaceTech's blessing, drilled an additional 1/32" hole in the emulator blow-off plate.
Final settings for me (180#):
RTFE at 2 turns
PJI 30 wt fork oil
Oil level: 5.1", fork collapsed with emulator, no spring)
20 cm PVC spacer resulting in 25-27mm SAG
© 1998 mattlai@hotmail.com
