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Friday, February 23, 2018

BMW Motorcycle Racing Tachometers

Like most vehicle manufacturers of the day, BMW did not produce its own tachometers for race bikes.  Rather, the task was out-sourced to premier instrument makers.

In the pre-war period, this job fell to Robert Muhle and Sohn of Glashutte, Germany. Muhle tachs were sourced for use on the BMW Type 255 Kompressor, as well as the twin cam racer R51RS.   Interestingly, the company remains in business, producing high end wrist watches.  Its no surprise then that a peak inside one of these instruments would have one believing that were viewing a ship chronometer.

R. Muhle Drezahlmesser

For the post-war Type 253 (colloquially known as the RS54), the original long stroke version was fitted with a 60mm VDO, complete with a weighted and balanced needle.

VDO 60 mm Drehzahlmesser

On the works bike, and later privateer RS54's, the more commonly found tachometer is a Smith's ATRC.  Generally considered to be the Rolls Royce of instruments, the ATRC were required to be mounted in a special vibration dampening holder. It was essentially a bezel mount connected to the instrument by means of large rubber O-ring.  

Smith ATRC Drehzahlmesser

Of interest, there was two ways to run the tach on the RS54.  Both a straight drive from the timing gear, or an angled drive from the front of the crank.  The straight drive is commonly found on solo machines, while the angle drive is more common to side cars, and the works type racer.  The works motors were occasionally fitted with a Bosch fuel injector which was driven by the timing gear shaft.  Therefore, the tach drive had to be relocated, and furthermore this allowed for clearance of the cable.

Tachometer drives for RS54

Buchanan's Does it Again

Special thanks to the guys at Buchanan's Spoke and Rim in Azusa, CA!  They went the extra mile getting the wheels for one of my race bikes built.  I love this setup.  Borrani Record rim mated to a magnesium Fontana 230 doppelduplex from brake, complete with magnesium shoes.  And of course Metzler tire. Aluminum nipples, stainless spokes.  Perfectly balanced as built without weights!  Thanks again guys.