This is from the site Bring a Trailer (https://bringatrailer.com/) ...
This 1981 BMW R100RT is a custom café racer built by the seller which is powered by a 980cc boxer twin paired with a 5-speed transmission and shaft drive. The seller acquired the bike in 2011 after restoring his father’s R50, and features include RaceTech-modified front forks, rear coilover assemblies from Works Shocks, a custom solo seat made by Thorsten Strenger, dual front Brembo disc brakes, an R90 final drive, Motorrad Elektrik ignition and charging system components, LED lighting, and more detailed below. The bike was featured on BikeEXIF’s site in 2013, and the seller has added 6,400 miles since its completion. This R100RT is now offered with a handwritten build log, a printed build log, tool roll, a BikeEXIF calendar featuring the bike, a copy of the magazine featuring the bike on its cover, and a clean New York title in the seller’s name.
The fuel tank, front fender, and rear clamshell are finished in matte black with white gold leaf offset racing stripes down the middle, and cream BMW-style double pinstripes. The seller has converted the bike to LED lighting, including the headlight, indicators, taillights, and license plate light. The plate is mounted to a custom aluminum bracket which follows the contour of the final drive.
The wheels were custom made by Woody’s Wheelworks to allow fitment of tubeless tires. They are based around an R65 front hub and R90 rear hub with stainless spokes and sealed aluminum hoops, and are fitted with Avon unidirectional tires. Braking is handled by dual front Brembo discs and a mechanically-operated rear drum. Custom wheel spacers machined by Chris Cantebury affix the R90 rear hub and final drive assembly to the R100 swingarm.
The factory front forks were rebuilt by RaceTech with their Gold Valve emulators giving the bike dual-stage damping. A few years after the bike was initially completed the seller had a set of 3.5″ fork extensions with built-in preload adjusters designed by Toaster Tan. The rear coilover shock assemblies were custom built by Works Shocks to the seller’s specs, and were later extended for additional suspension travel.
The custom solo seat was made by Thorsten Strenger in Florida. The seat is designed to fit on a shortened factory seat frame, and to pair to a stock BMW tank. The brown leather cover and cushion were made by the seller’s local upholstery shop. A 12-volt Alien Motion lithium-ion battery is affixed to a custom pan made from a road sign and concealed under the fiberglass rear clamshell.
A CNC-machined triple-clamp from Toaster Tan is fitted and sits lower on the forks than the factory item, allowing the Tarozzi clip-ons to be mounted over the triple clamp rather than underneath for a more upright riding position. The steel bars are fitted with factory BMW controls, and the footpegs and controls have been relocated with a set of Boxer Metal rearsets designed for airhead BMWs.
The Acewell multi-function gauge incorporates a digital speedometer and an analog tachometer, and the housing has been hand-brushed for a satin texture. The gauge incorporates indicator lights for high beams, directionals, and the rev limiter, and includes a ride timer, odometer, trip meter, and a voltmeter. Approximately 6,400 miles are shown, which is the total mileage since completion.
The 980cc air-cooled boxer engine was reportedly rebuilt to stock specifications prior to the seller’s acquisition, and sends power to the rear wheel via a 5-speed transmission and shorter R65 final drive. Modifications include an Epco stainless steel exhaust with reverse-cone mufflers, a Motorrad Elektrik Alpha Electronic ignition system, and Motorrad Elektrik diode board, stator, and voltage regulator, which are pictured in the gallery below.
A custom aluminum toolbox is installed on the factory battery tray and houses a 12-volt mini air pump, a tire plug kit, and a tool roll with a selection of hand tools, a multi-tool vice grip, and an LED flashlight. The seller opted to retain the factory center stand in addition to the side stand for ease of repair, and an air pump and plug kit are included for the tubeless tires.
The seller has kept a handwritten log of work performed since 2011, as well as a printed spiral-bound book that is more than 600 pages long and incorporates both the seller’s handwritten notes and forum activity from the duration of the build. The bike was also featured as one of Bike EXIF’s top ten custom bikes of 2013, and the Bike EXIF calendar featuring the bike is also included, as well as a copy of the magazine which features the bike on its cover. A video highlighting the build is viewable below.