This rebound separator valve,...
This rebound separator valve, at left, and Gold Valve, above left, assemble on the shaft of the Suzuki's stock shock, below left. The separator keeps rebound damping adjustments from affecting compression damping.
Race Tech Suspension for Suzuki GSX-R600
With an increasing number of aftermarket suspension companies offering complete drop-in cartridge kits for sportbike forks, it was only a matter of time before Race Tech, creator of the original Gold Valve cartridge emulator, jumped into the fray. The company recently completed development of a 25mm kit and has also been working on some interesting internals for stock rear shocks. We sent over parts from a GSX-R600 racebike belonging to friend-of-the-magazine and racer Corey Neuer and asked Race Tech to install its latest upgrades.
The 25mm cartridge kit includes replacement base units that are interchangeable between practically any sportbike fork. Adapter kits, used to match the base units with the bike's fork caps and bottom mounts, are provided separately; the idea is that you can buy the cartridges for one bike, then transfer them to a new bike and only have to purchase the adapter kit. The cartridges incorporate some innovative features, such as a combination of O-rings and bumpers for bottoming rather than a hydraulic stop, and digressive valving (in which the shims on the valves are preloaded to provide a very specific damping curve). Each fork was buttoned up with a Race Tech fork spring and the company's own fluid. Total cost for the rebuild was $1575, including the cartridges, adapters, springs, fluid and labor.
The stock rear shock was disassembled and rebuilt with a Gold Valve, also with digressive valving. The company has recently changed its approach to roadrace shock valving as a result of extensive on-track testing that is still ongoing. An interesting addition to the shock was a rebound separator, which stops changes in the compression damping adjuster from affecting the rebound adjustment (as is the case with many shocks and forks). Another change was to the top-out springs in both the fork and shock. While many stock and aftermarket setups use long, soft top-out springs in an effort to keep the tires on the ground under acceleration or braking, our GSX-R setup had short, stiff top-out springs intended to keep the bike from jumping off the ground in quick transitions. The shock rebuild cost $453, including the Gold Valve, rebound separator, spring, collar, fluid and labor.
Conveniently, Neuer has two almost-identical GSX-R600s. One bike is set up with hlins 25mm cartridges and an hlins shock, and we used that bike as a baseline while the other bike was fitted with the modified fork and shock. We rode both bikes at a Buttonwillow track day hosted by The Track Club (www.thetrackclub.com) with Race Tech's Lenny Albin providing trackside support for both bikes. As with practically any aftermarket suspension, both bikes were set up much stiffer than stock, with the 25mm cartridges providing more support on the brakes. Overall, we were impressed with the Race Tech components, which in our limited test offered benefits compared with even the hlins suspension on the second bike.
The Race Tech bike felt stiff in general, but big hits were easily soaked up. The suspension performed better the harder it was worked, which Albin says is a characteristic of the digressive valving. Stability was excellent over Buttonwillow's increasingly bumpy surface, with the bike tracking straight over bumps that would unsettle the hlins-suspended bike. Surprisingly, the modified stock shock didn't fade at all, even in 90-plus-degree heat and over the course of multiple 20-minute sessions. Albin noted that traditional fluid breaks down when the polymers shear, but the Race Tech fluid has a different base with no polymers-hence no shearing and no fading.
Our man went close to a second quicker around Buttonwillow's full circuit on the Race Tech bike than on the hlins bike, citing more confidence and better stability as the major factors. That's impressive for a stock-based shock and first-run cartridges against long-developed hlins parts. Certainly a one-day test on one bike is not an all-encompassing evaluation when it comes to the nuances of suspension, but we would definitely consider the Race Tech parts a viable alternative to the established players in the market.
Race Tech
(951) 279-6655
www.racetech.com
Metzeler Roadtec Z6 Sport-Touring Radial
Intended as a replacement for the company's very popular MEZ4 sport-touring radial, Metzeler's new-generation Roadtec Z6 employs all of its latest technological advancements in compounding, tread design and profile, all built around the patented 0-degree steel belt radial construction. A new compounding extrusion process (called Fine Carbon Matrix) allows use of the latest high-performance polymers, which Metzeler claims deliver up to a 20 percent improvement in dry pavement grip over the MEZ4. The Roadtec Z6 also comes in two carcass constructions in the most popular rear size (180/55-17): one optimized for bikes less than 530 pounds, and one for bikes exceeding that weight, with the tires' structural characteristics tuned for each. New tread patterns with different land/sea ratios (the ratio of tread grooves to rubber in contact with the pavement) are designed to improve wet-weather handling, feedback and grip (again based on Metzeler testing).
Metzeler's new CMT (Contour Modeling Technology) permits combining different designs across the tire profile, with each one optimized for a particular lean angle. New sidewall construction specifically tuned for sport-touring bikes is claimed to provide improved bump absorption and tire compliance on rough or pitted surfaces. The Roadtec's carcass is also claimed to provide better damping characteristics over bumps for more comfort for both the rider and passenger.
We spooned a set of Roadtec Z6s onto our Suzuki Bandit 1250S test bike and immediately noticed a significant improvement over the stock Dunlop OEM-spec D218 that came as standard fitment. Steering characteristics were more neutral, with the added bonus of being more precise at higher speeds. Overall ride and bump absorption-both at major lean angles and upright-were much improved over the Dunlops, with far less harshness over sharp bumps while still providing excellent stability at all speeds and cornering situations. Unlike some tires that tend to deflect over bumps, the Metzelers tracked straight and true over nearly all pavement irregularities we ran them on.
Overall grip was better by a substantial margin as well, especially while leaned over. While feedback wasn't as communicative as we'd like, the Roadtecs still offered enough to instill more confidence when ramping up the pace. Another sign of the improved grip was while braking; the Metzelers allowed a much higher threshold of braking before the Bandit's ABS system would take over, supplying a higher level of safety in urban traffic situations. We didn't have the opportunity to put the Roadtecs through their paces in the wet, so we can't offer a judgment in that area.
We can say, however, that the Metzeler's definitely wear very well despite their excellent grip in the dry. The Roadtecs were showing very little wear after 1500 very hard miles that would have quickly shagged regular sport tires.
The Metzeler Roadtec Z6 is offered in a wide variety of sizes. Available in front sizes 110/70ZR-17, 120/60ZR-17, 120/70ZR-17, 110/80ZR-18, and 120/70ZR-18, and 150/70ZR-17, 160/60ZR-17, 170/60ZR-17, 180/55ZR-17, 190/50ZR-17, and 160/60ZR-18 rear sizes. Prices range from $146.99 to $162.99 for fronts; $185.99 to $236.99 for rears.
Metzeler Motorcycle Tires
(800) 747-3554
www.us.metzelermoto.com