Sea Otter 2015 – Manitou Magnum Pro Fork

by Brian Mullin on April 23, 2015


The Manitou Magnum is a purpose built Plus specific suspension and comes in 27.5+ and 29+ sized configurations and can fit up to 3.4″ wide tires. The forks have a 34mm chassis, a hollow crown, their strong reverse arch design and have an 110 x 15 axle spacing utilizing their QR15 Hexlock. The 27.5+ has a 48mm offset and comes in 80-140mm of travel while the 29+ has 51mm offset and 80-120mm of travel. In addition, the Plus fork was given ride heights that retain the bikes proper geometry, so they have a shorter than usual axle-to-crown height. The forks retail for $900 and are available now.


Although fat tires offer comfort, traction and control on less than ideal terrain, their size and weight cause kinetic energy issues during initial stroke and bigger bumps, exacerbated by the muted impacts due to low tire pressures. They optimized the Magnum fork for the Plus tires and their increased un-sprung weight and it offers compliance for everything from small bumps to big hits. During the initial stroke, it lets the tire easily move without overcompressing.  On bigger bumps, the fat wheels mass creates a greater kinetic energy and causes an overstroke and this builds up unnecessary spring energy, and this in turn is pushed into the rider followed by the corresponding high rebound velocity. The Magnum was designed to get the right balance between initial stroke movement and high-velocity control.



    • Spring
      • Dorado Air – single input to charge positive and negative air chambers for perfect spring balance providing unmatched small bump compliance.
      • Dynamic Over Stroke – eliminates dwell at top out and provides a seamless transition from extension to compression resulting in a smoother stroke.
    • Damping
      • MC² -Multi Control Compression: Platform, High and low-speed adjust.
      • IPA – Incremental Platform Adjust: Used to dial in the perfect amount of pedaling platform.
      • TPC – Twin Piston Chamber: rebound damping, custom tuned for plus sized rolling stock
      • Externally adjustable HBO – Hydraulic Bottom Out, derived from the award winning Dorado to provide a bottomless feel

Magnum Air Spring

The Dorado based air spring system pressurizes the positive and negative side of the piston at the same time to the same pressure, so the force is almost the same on both side. At the top out you can easily start movement since there isn’t any preload to overcome and offers perfect spring balance that provides an unmatched small bump compliance.

The D.O.S. (Dynamic Over Stroke) smooths out the transition from the rebound to compression in the most extreme conditions (top out). They tune the top out to deal with excess kinetic energy, allowing the fork to overextend a few mm for better deceleration when coming off high-velocity rebound events and not transferring those loads to the rider.


They have a new volume adjust system named Incremental Volume adjust (IVA), and it allows the rider to customize the air volume based on riding style or terrain. You alter the positions of the black 10mm spacers to move the white piston around to adjust the volume. It has four available positions and the spacers always remain in the fork so the spacers won’t be lost in your toolbox or shop.


Magnum Damping

The damping uses their TPC+ or Twin Piston Chamber damper system that utilizes two pistons, one for the rebound, and the other for compression. The oil is always being squeezed under positive pressure, so there isn’t any cavitation. In compression, the shaft entering the fluid column pushes oil through the compression circuit. In rebound, the oil underneath the rebound piston is getting squeezed between the end cap and piston and is then pushed through the rebound circuit.

The compression side uses their MC² Damper (Multi Control Compression) Platform, which has high and low-speed adjustments. The red low-speed lever has a range from descend to climbing mode while the black high-speed dial was designed to create a platform adjuster by controlling the shim stack. In the center of the high-speed dial is the adjustment for the HBO.


The HBO (Hydraulic Bottom Out) works on top of the rebound circuit and when its compressing it enters into the cuff and the oil squeezes out through a small hole and works the last 25mm of travel. Its position dependent but the amount of force it creates depends on how hard you approach bottom out, so on big hits it creates a lot of energy to resist the hard bottom outs.

Finally, a dual bottom out bumper system exists for the last 5mm of travel, for a softer settling instead of a harsh impact. Having a bumper at the bottom of each leg equalizes the load across the fork, preventing any twisting problems.


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