is six foot, six inches tall and weighs in at 289 pounds on a good day, so as one may expect, there are not many dual-suspension trailbikes out there that can either fit him, or that can manage to perform well enough to make him happy. Sheppard also prefers the durability and simplicity of a single speed, which further reduces his shopping list - and eventually led him down the path to making his own bikes. To that end, Sheppard founded Ram Bikes a number of years ago and his latest creation is an efficient-pedaling one-speed with seven inches of wheel travel on both ends. Like all of his designs, it is both wild looking and functional, and he'll make you one if you say please. Although he considers frame building as a hobby, a steady stream of like-minded customers may eventually force him to take up the TIG torch full time. Sheppard dropped in to the Pinkbike Dome at Sea Otter to show us his latest masterpiece.Ram Bikes URT Chassis
The RAM chassis is essentially the same as the old-school unified rear triangle designs of the mid 1990’s. The bottom bracket is attached to the swingarm, which in the case of this design, pivots on a four-bar linkage near the intersection of the seat tube and top tube. The advantage of a URT design is no-bob pedaling when the rider is attacking out of the saddle. Sheppard says that, while most observers believe that the bottom bracket's vertical travel is excessive, the four-bar linkage is configured instead to move the BB fore and aft so that it does not overtly affect pedaling.
There is no front triangle. Instead, a single, large-diameter chromoly pipe connects the fork to the swingarm, creating a chassis that looks about as simple as a dual-suspension design can be made. Reason two for the RAM's unified rear end is that the chain length is stable through the suspension's travel, which means that Sheppard's design is well adapted to single-speed applications. For geared riders, no chain growth means that a mid-length derailleur cage should be enough to handle any one-by drivetrain.
RAM Quadrilateral Fork
Sheppard's coup de grace
this year was a 180-millimeter-travel leading-link suspension fork borrowed from a similar motocross fork design by Valentino Ribi
. The fork uses a four-bar linkage to create a nearly straight axle path which traces the head angle within an eighth of an inch (4mm). As a result, the quadrilateral fork feels and steers like a conventional telescopic design with the exception of one important aspect: it has much less stiction.
The linkage pivots run on small-diameter, smooth-acting ball and plain bearings, while suspension and spring duties are handled by a single Fox Float X Kashima CTD shock. The smaller swept area of the shock and the fact that the quadrilateral fork drives it at bit more than a two-to-one ratio helps reduce starting friction and reportedly, makes for a much more responsive fork.
|I discovered that one brake heated up too much on the longer descents, so I added the second brake. Now I never worry about heat at all.|
Four-bar forks are neither new nor revolutionary, but in the context of the RAM project, it makes sense, especially considering that Sheppard shreds long descents like the Downieville DH on a regular basis, so he needs a responsive, long-stroke fork that can take a beating. The uppers and lowers are chromoly steel, while the articulating links are water-jet cut aluminum. Down below, the massively wide front hub is actually two Azonic front hubs, cut down and joined at the center so Sheppard could use two disc brakes. A splitter beneath the fork "crown" sends brake fluid to both front brakes from the left-side lever. There is no welded or mechanical joint to transfer braking torque from one side of the fork to the other. Instead, the left-side spokes handle the torque of the left side brake and the right side spokes take care of braking on the right. Sheppard said: "I discovered that one brake heated up too much on the longer descents, so I added the second brake. Now I never worry about heat at all."
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