MXA TEAM TESTED: COPPERSMITH AERO/HYBRID SPRING CONVERSION KTM FORK KIT

WHAT IS IT? Most KTM Pro riders elect to pay the price for WP Xact Pro Cone Valve spring forks because they allow the front end to follow the ground better than the stock WP Xact Air forks. Properly valved coil-spring forks deliver a connection to the ground that improves steering response. MXA test riders like the consistent and supple feel of WP’s unique Cone Valve damping system. It should be noted that replacing the stock WP AER air forks with the XACT Pro Spring forks adds 3 pounds to the front end of the bike, and, to sensitive test riders, that is a big deal; however, MXA test riders  accept the weight for the improved feel.

WHAT’S IT COST? $995.00 (installed in your fork—includes fork spring and oil).

CONTACT? www.coppersmithracing.com or (330) 724-2900.

WHAT STANDS OUT? Here’s a list of things that stand out with Coppersmith Aero/Hybrid WP/Ohlins fork kit.

(1) Spring conversion kits. Obviously, WP Cone Valve forks are only one way to convert KTM forks from air to coil springs. Virtually every major suspension company offers an air-to-spring kit for WP forks, some that use Kayaba internals and some that design their own system. Plus, Kayaba, Ohlins and even WP offer complete air-to-spring conversion kits. Prices range from $600 to $2000‚ and in many cases that does not included the fork springs or re-valving.

(2) Coppersmith Aero/Hybrid kit. There is one air-to-spring conversion kit that combines the best of both worlds. It comes from Coppersmith Racing, famous for its Ohlins suspension setup. The Aero/Hybrid conversion kit has a very unique take on how to build a WP fork that combines the best of both coil-spring and air technologies. It combines the smoothness of a spring fork with the tunability of an air fork. The Coppersmith Aero/Hybrid fork kit replaces the internals in the stock WP damping leg with a modified Ohlins TTX22 spring cartridge (and coil spring) and leaves the stock WP air fork leg untouched. In essence, the Aero/Hybrid fork kit is 50 percent Ohlins (damping) and 50 percent WP (air spring).

(3) Combination. The Coppersmith kit allows racers to use their existing WP fork legs and Coppersmith does not touch the stock WP air leg, only the damping leg of the WP fork is modified by upgrading the damping with Ohlins TTX22 cartridge kit. The TTX technology has a positive pressure balance system, thanks to its twin-tube technology. The gas-pressurized dividing piston inside the cartridge pushes the hydraulic fluid back into the low-pressure side, and the result is improved performance and zero cavitation.

(4) Weight. The Coppersmith Aero/Hybrid fork kit is lighter than the typical air-to-spring conversion for four reasons: First, the heart of the system is built around an 8mm hollow steel shaft, and the main piston is 22mm in diameter. Second, the vast majority of the Ohlins internals are made from aluminum. Third, the Coppersmith Aero/Hybrid fork kit only uses one fork spring, which saves weight and, because this is a hybrid air/coil system, the spring rate of the single spring doesn’t have to be as stiff as on most air-to-spring conversion kits. Finally, since WP’s air leg remains fully functional, the Aero/Hybrid fork kit utilizes it as part of the overall design. Boiled down to its essence, you have an Ohlins fork on one side doing the damping and a WP fork on the other side holding the air pressure.

(5) Ohlins tech. A word about Ohlins: Ohlins makes the TTX22 cartridge kit to convert WP air forks over to coil springs. To achieve this, Ohlins uses two TTX22 cartridges and two coil springs (eliminating the WP air system). The Ohlins kit changes both legs over to coil springs, which adds to the price and the weight. The Coppersmith Aero/Hybrid fork kit uses Ohlins damping system, but it is not a kit that Ohlins offers—it is a Coppersmith Racing exclusive.

(7) Performance. For our Vet and slower test riders, MXA ran a 4.5 N/mm fork spring in the damping leg with the compression and rebound clickers set on 14 clicks out. In the WP air fork leg, we ran 55 psi. Why so little air pressure? Because the 4.5 N/mm coil spring handles all of the initial fork control, and the low air pressure doesn’t interfere with the fork feeling like a coil spring fork. In fact, it felt identical to an Ohlins coil-spring fork. Then, as the fork moved upwards in its stroke, the air pressure inside the WP leg increased to provide “big hit” hold up and bottoming resistance. Riders could fine tune the feel of the forks with Ohlins compression and rebound adjusters.

It should be noted that Ohlins clickers are much more effective than Showa, Kayaba or WP adjusters. It felt like one click was the equivalent of two clicks on a normal fork. Test riders never varied more than a couple clicks in either direction to get the fork dialed in. Additionally, the air pressure can be increased or decreased to change the fork’s overall resistance. We used the zip-tie method to choose the best air pressure setting. We set the pressure until we had one inch of unused travel between the zip-tie and the fork’s bottom; however, if the air pressure had to be increased above 95 psi, we traded the 4.5 N/mm fork spring for a 4.7 N/mm spring. This was the spring rate (4.7mm) we ran for fast Intermediates and Pro riders.

WHAT’S THE SQUAWK? We don’t have any complaints..

MXA RATING: The idea behind the Coppersmith Aero/Hybrid fork kit is to use the Ohlins TTX cartridge and coil spring to handle the small- to medium-sized bumps and, as the fork moves through its stroke, to have the air pressure kick in to stiffen the forks. When set up properly, you get the supple feel of a coil spring with the bottoming resistance and consecutive-bump recharging of an air fork. Test riders loved the Coppersmith Aero/Hybrid fork kit. The Coppersmith Aero/hybrid kit saves weight over a traditional coil-spring fork, cuts shipping cost by half, and gives it Ohlins damping. It retails for $995 (installed in your fork). For more information, call Coppersmith Racing at (330) 724-2900.

 

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