The Monkey Lab: Schlumpf-Equipped Brooklyn Machine Works Gansta Fixie

15 January 2012

Schlumpf-Equipped Brooklyn Machine Works Gansta Fixie

When Schlumpf redesigned their clutch plates to make them compatible with fixed gear bikes, Neil wanted a unique frame to test/showcase a Speed Drive unit. The Brooklyn Machine Works Gansta Track frame fit the bill with its pierced top tube, box-section fork crown, and airfoil fork legs, seat stays, and chain stays. Only problem - the frame had no provision for a brake. After a couple calls to BMW and some brainstorming on their part, they agreed to fabricate a disc brake mount for the fork. Now we were in business.

The frame got a sparkly clear coat over a gloss black base, so we wanted to use shiny silver wheel parts to compliment this finish. We went with polished Phil Wood hubs - 32 hole bolt on disc front and 36 hole fixed/fixed bolt on high flange track rear- laced into bright silver Velocity Deep V's using Sapim Race spokes and brass nipples. A 2 leading/2trailing lacing pattern was used on the front and a 3 leading/3 trailing lacing pattern was used on the rear. Spoke color (black/silver) was alternated between each bundle of spokes (bundles of 4 on front wheel, bundles of 6 on the rear) to give the wheels contrast while spinning.

The heart of the project was the hidden gear box. The Schlumpf systems give you two gear ratios using a single chain ring that is connected to a two-speed internal gear system encased in the bottom bracket. The Speed Drive model offers a ratio change just slightly larger than a standard road front derailleur and double crankset (65% change). Since the chain remains on a single ring, a single speed or fixed gear bike with a tensioned chain can become a 2-speed. The updated clutch plate design allows the gear box to transmit torque in two directions, making it compatible with fixed gear bikes.

The gear ratio is changed by intentionally knocking buttons on each side of the bottom bracket axle with your heels (silver button in the center of the crank set). In one mode, the Speed Drive acts like a standard bottom bracket and crank set: the chainring and crank arms spin at the same rate. In the other mode, the Speed Drive gearbox over-drives the chainring: the chainring now spins faster than the crank arms, providing a larger effective chainring size.