This dyno graph of the stock Yamaha fork (below) shows the compression damping adjuster needle (left) has no effect after just a couple of clicks out. The GP Suspension needle (right) has a subtler taper to provide more adjustment range.
The new inverted fork on the R6 does offer some improvements over last year's conventional unit and previous inverted Showas as well. "Most of your stock cartridges are aluminum-based rods with a coating on them, and you can't polish the coating off because it wears the aluminum out," says Hodges. "The R6 has a steel rod. You can polish it, but they come from the factory with a pretty finely polished rod to try and reduce stiction. They've changed the upper tubes where they put both bushings fixed in the tube [rather than one bushing in each tube], so you don't have two bushings changing locations and the rigidity of the fork. Showa just went [to that configuration] last year; Kayaba's been doing it for about five years. Showa finally got on board with the '04 GSX-R600/750 and switched to two fixed bushings to keep the rigidity in the fork."
The first setup I tried on the GP Suspension bike included a stock shock and fork with a mix of stock and the company's own internals. Hodges produced some interesting dyno charts that showed the R6's fork compression adjuster has no effect after just a couple of clicks out. An adjuster with a longer, shallower taper replaces the blunt stock piece. Citing insufficient damping in the stock compression valves, GP replaces the stock piston with its own valve and shim stack. "My valve is different. I've never seen one out there, either OEM or aftermarket, but maybe someone's built one. It's a 20mm piston with a five 2mm-hole port configuration with a 17mm shim base. Ohlins does four 1.6mm holes, [and Honda's] HMAS does something similar." On the rebound side, the stock piston is used with a new shim stack.
GP's replacement fork valves (above, right) have sets of five damping orifices as opposed to the usual three or four (above, left). This forces the shim stacks to open more uniformly, providing better control over flow (and damping).
Hodges says the new inverted fork on the R6 doesn't use its full travel because the inner tube bottoms on the fork cap before anything else, so he trims 5mm off the tube to liberate that last bit of travel. Finally, stock springs were used to accommodate my 140 pounds, and each tube was filled with Motorex 5W oil.
Inside the Soqi shock, Hodges retains the stock piston with his own compression and rebound shim stacks and drills and taps the reservoir cap to accept a Schrader valve. A 4.5mm shim was slipped under the shock's clevis to raise the rear ride height, and the fork tubes were dropped from their stock height by 8mm, placing the tops slightly inside the clip-ons. "You're trying to give [the swingarm] more downslope to get better rear-end traction. Once you go to some of the bigger tires [which the D208 GP JLB is compared to stock] and put too much ride height in the back, you lose the trail, so you have to push the forks down to get the trail back for straight-line stability. Rear grip, front-end feedback and front grip are what we're trying to get out of the bike, and also keep it stable at the same time."