Rear Drive Ratios

Variables for the chart are your actual on-the-road tire diameters (modest effect); tire pressures/temperature (tiny effect). The variation in UNLOADED diameter of a 4.00-18 rear tire versus a 120-90×18 rear tire is about 15 mm in the WORST case I know of. However, the actual rolling circumference varies little (probably about 2%, but could be larger). Hence the values shown below are THEORETICALLY fairly accurate, and some are taken from a BMW chart dated 1978, others are calculated, and some are actual test data.  Values are theoretical; and do NOT account for tire slippage and tire variations, nor for speedometer and tachometer variations.  Because of these factors, rpm is LIKELY higher for a true speed as charted.

See notes at end of this article!!  The speedometer ratio is printed on the dial of most speedometers.  The author’s website discusses things in much more depth, and includes expanded ratios for earlier models, etc…..link at the end of this article.

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R100GS Ohlins Shock Installation

After experiencing the amazing performance of Ohlins shocks on the K12, it was a forgone conclusion that the Works Performance damper on the GS would be replaced in short order. A quick FAX to Wim Kroon had one on its way, with instructions to fit a spring one weight lighter than standard. When it arrived, I used a home grown collection of threaded rods and drilled plates to remove the spring, which was sand blasted and painted black (I didn’t need or appreciate Ohlins’ bright yellow advertising clashing with the custom paint). Mounting took only a few minutes, the key being to drop the swing arm enough to allow the top end of the shock to slip between the mounting plates on the frame.

The most difficult mounting decision was where to locate the remote adjuster. Since no mention was made in the installation instructions, I decided to fabricate a small bracket that let me put it in front of the left swing arm pivot where I’d have easy access.The scrap box yielded a piece of 1/8″ x 1″ aluminum which, with the addition of a few holes, proved worthy of the job. Ohlins had seen fit to include plenty of line between the shock and adjuster, so there were no worries there. I’ve since learned that the recommended location is on the right side of the luggage rack, even with the rack’s end. On bikes I’ve seen using this setup, I found the knob hard to reach and even harder to turn, so I’m happy with the new location.

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Driveshaft Bolts, the split lock-washers…..and, push-starting cautions

The four TRANSMISSION OUTPUT FLANGE BOLTS CHANGES;…split lock washers, updates, …and….pushstarting! © Copyright 2021, R. Fleischer https://bmwmotorcycletech.info/drvshftboltstoolstorque.htm 47 Background and History on these 10 mm 12 point bolts and lockwashers used at the transmission output flange: The earliest bolts for the /2 & the Airheads (transmission output flange-to-universal joints)  had steel split-type lock-washers, & were […]

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