MXA TEAM TESTED: KREFT MOTO PLUSH TANK

WHAT IS IT? Do you remember the subtank craze of 2003–2008? Subtanks were air chambers, typically made from carbon fiber tubes and hidden behind the front number plate. These empty chambers attached to the fork’s air-bleed holes, and at low fork speeds, air could easily move through the adjustable dial and into the carbon fiber tanks, making the forks think the oil height was lower. Lower oil height makes forks feel softer. Conversely, when the fork speeds were higher, the air could be restricted from moving freely through the valve, resulting in the forks feeling like they had a higher oil height (stiffer). Additionally, you could close the valve to go back to the fork’s air volume without the tanks attached.

For all of its similarities to the Enzo subtanks, the Kreft Moto Plush Tank is nothing like a subtank. The Plush Tank has nothing to do with the fork’s oil height or tricking the fork into thinking the oil height is low or high. Instead, the Plush Tank attaches to the air leg of a WP air fork. The only oil in the WP air leg is a small amount for lubrication of the internal parts, thus the Plush Tank doesn’t change the fork’s damping by tricking the fork’s oil height. Instead, it allows the rider to change the volume of the main air chamber.

WHAT’S IT COST? $295.00.

CONTACT? (541) 797-0700 or www.kreftmoto.com.

WHAT STANDS OUT? Here’s a list of things that stand out with the Kreft Moto Plush Tank.

(1) Spring characteristics. A coil steel spring has a linear compression ratio. It gets stiffer at a constant rate of change. Not so with an air spring. As an air fork compresses, the spring rate increases exponentially. This is called a hyper-progressive spring curve. It makes the last couple inches of travel create a massive increase in the air’s spring rate. That makes an air fork very harsh at the end of its stroke.

(2) Boyle’s law. The Kreft Plush Tank takes advantage of Boyle’s law, which states that there is an inverse relationship between pressure and volume. In action, this means that the pressure of a gas (air) decreases as the volume of the container increases. That is the basis of the Kreft Plush Tank. Using Boyle’s law, Kreft was able to manipulate the air pressure inside the WP air fork by flipping a switch on the side of the Plush Tank. When the switch is in the Firm position, the Plush Tank is shut off from adding volume to the WP fork leg; however, when you flip the switch to Plush, you open up the airway between the fork leg and the Plush Tank, which increases the volume of the main air-spring chamber. And, according to Boyle, as the volume of the container goes up, the air pressure goes down.

(3) In action. The Plush setting increases the volume of the main air spring chamber, giving your WP air forks a more linear spring curve. The fork will feel softer, dare we say plusher, instantly. You’ll feel improved compliance and softer settings on technical trails. Hit a favorite loop or trail or ride back-to-back laps in each setting and you will feel the difference. Flipping the switch back to the Firm position returns the fork’s volume back to its original stock setting, which is stiffer and better able to handle big hits.

(4) Performance. Obviously, the best possible use for the Plush Tank is for a rider who rides tracks one day and woods the next. It is like having two forks in one; however, a motocross-only rider would be much better off having his forks valved specifically for motocross and just relying on damping and air-pressure adjustments for off-road.    

WHAT’S THE SQUAWK? There is a real concern about air leaks with the multiple high-pressure fittings.

MXA RATING: The Kreft Plush Tank works by manipulating the volume in your air forks. It can make your forks plusher with the flick of a switch or make your forks stiffer by reversing the process, but even Kreft will tell you that you need to re-valve your forks to work best in one setting or the other.

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