Christchurch built Sharratt 150mm Full Suspension Prototype

The folks at Bikecycle.co.nz, namely Craig Sharratt, have been a busy lot. Between organising the South Island’s first Enduro event and distributing a bunch of amazing European brands, they’ve somehow found time to design and build a prototype 150mm travel trail bike, and there are plans for more too. The quality of the build is pretty damn impressive, although it’s worth bearing in mind that the prototype pictured is exactly that, a prototype. It will feature ISCG 05 tabs in its final form as well as internal routing to accommodate RockShox Reverb Stealth and will be a more fine tuned version of what you see here. We just recieved a bunch of info on the frame which should answer every question you have apart from, ‘can I have one?’ and ‘when can I have one?’

The Sharratt 150mm features:

• Dual bushing rear pivot. There are two sets of flanged bushings at the seatstay near the dropout. One is the actual pivot, the other has just enough play to allow 1.4 degrees of rotation through the full travel and is there only to provide better lateral stiffness of the rear end. The flanges of the bushings slide on laser cut stainless steel surfaces while the pivot pin is also stainless steel for durability.

• The entire dropouts are replaceable rather than a hanger that flexes under shifting. The dropouts have removable inserts for either a Syntace X12 or Maxle setup. If someone wants it we will have an option that within the dropout there is a replaceable hanger.

• CNC machined chain and seatstays from solid billet with reinforcing bridges inside the stays. This costs us a fortune to machine but means the stays are stiff and we can have a good tyre clearance by making the stays narrower at key areas but reinforcing them internally at these points to minimise flex that would happen if a hollow tube was used. Even with a large 2.4 Schwalbe there is enough clearance.

• Bonded construction. We wanted to eliminate the weak points that seem to specifically be the end of the weld of the shock mounts and the drive side chainstay where the bridge welds on. The chainstays, pivot link plates and bridging tube are all mechanically locked into place as well as bonded. The top tube shock mount is machined from solid block and is bonded to the top tube. The pivot points have flanged pins that lock through the top tube and are bonded to the external cups on the outside of the tubes. All this of course needs to be fatigue tested but it seems that entirely welded construction is no longer adequate for modern mountain bikes.

• Internal cables entering at the head tube through a machined cable guide. Many bikes that just cut holes in the head tube have issues with the cables getting cut on the headtube edges so we made a cable guide that is bonded into the head tube. The bike will use a Reverb Stealth post.

• Geometry on this bike is low, slack and long: 66.5 head tube, BB level with axle centre line, 615mm top tube on a medium size. Designed to run a dual or single ring with 170mm cranks (shorter cranks have been tested to have no significant drop in a rider’s power output. Crank length must vary by more than 5% before it impacts a riders pedalling ability, and shorter cranks actually have benefits in aiding a more even torque profile). Geometry can be customised easily though and will be an option. We will offer a higher BB option, 10mm top tube increments, and two or three head tube angles, with any combination of any of these options.

• The issue we have identified is that the rear pivot and stays are so stiff that it is exaggerating play at the main bearings, causing unwanted flex. We are going to look at running collet style bearing pins or even going to large diameter flanged bushings. The seatstay/top tube junction will have a gusset, we just haven’t decided on how it will be made yet.

More pictures can be found on the Bikecycle.co.nz Facebook page www.facebook.com/pages/BikeCycle-NZ/ which will be updated regularly.