A Mirror Bagatelle

Written by Rich Morin.

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Precis:  mirror modifications on a BMW R80ST

See Also:  BMW R80ST Modifications

This note describes a series of modifications I’ve made to the mirrors on my BMW R80ST motorcycle.

bagatelle noun (SMALL AMOUNT)

something, especially an amount of money, that is small and not important:
A thousand pounds is a mere bagatelle to him.

https://dictionary.cambridge.org/us/dictionary/english/bagatelle

Many motorcyclists seem to consider mirrors to be a minor (i.e., “small and not important”) consideration. And, if they’re always driving faster than everyone around them, this may be largely true. However, as a slow-riding geezer, I like to be able to see what may be coming up behind me. So, I’ve played around with a variety of rear-view mirrors and mounting approaches.

The Stock Setup

The R80ST’s mounting arrangements for mirrors consist of two holes, located next to the bases of the brake and clutch levers. These holes were originally used to mount a pair of circular, flat mirrors, about 4” in diameter. Although the (10 mm) holes are threaded, the stock mirrors did not take advantage of this. Instead, their (8 mm) shafts went through the holes and met a lock washer and a lock nut on the other (bottom) side. This seems a bit hacky for the exalted Bayerische Motoren Werke (BMW), but it’s actually a perfectly serviceable approach.

The Napoleonic Era

That said, I soon replaced the stock mirrors with some black plastic mirrors, made by Napoleon. These were convex, larger (about 3.5” x 5”), and rectangular. This let me see more of my surroundings without the need to move my head into a particular position. Although these served me well for many years, they eventually became difficult to adjust. In addition, there were some emerging maintenance issues.

Because these mirrors did use the threaded holes, removing them required swiveling them through the space now occupied by my windscreen, etc. So, I recently started looking around for another solution. I wasn’t sure what the end result would be, so I decided to try some inexpensive experiments. eBay has a lot of overseas vendors who offer inexpensive products, particularly if one isn’t in a big hurry. So, that’s where I’ve been shopping…

Degrees of Freedom

I began with an fairly inexpensive ($20) and very promising pair of mirrors. They have several adjustable joints and I was particularly pleased by the multiple degrees of freedom (4) this offered. Unfortunately, the actual mirrors aren’t what I wanted. The bodies are pointy and small; the lenses are flat, rather than convex. I inquired about alternative mirror bodies and was told (basically) that there weren’t any.

So, I thought about ways to improve the situation. I could probably fashion an adaptor (or even new mirror bodies!) using SketchUp and some 3D printing. However, I don’t really want to work that hard and there’s no guarantee that I’d be pleased with the result. Also, although the design is extremely adjustable, it also seems to need frequent adjustments. So, I’ve decided to call this an educational experiment and move on.

My current setup is based on another inexpensive ($17) pair of mirrors. These are largish (about 3.5” x 5.5”), convex, and roughly rectangular in shape. The production values aren’t going to win any awards, but they seem to be quite functional, providing great views of approaching vehicles. They are also pretty robust: a recent spill scraped some chrome off the plastic shell, but didn’t bend or break anything. In short, they are well worth what I paid for them. In fact, I bought two more pairs, to serve as spares.

Details, Take 1

Working out how to mount these mirrors has been an ongoing design project. I wanted a flexible approach that would make maintenance convenient (e.g., no need to remove the windshield). I also liked the idea of raising things away from the controls. My solution was to raise the mounts up on a pair of long bolts. I’m quite pleased with this approach and am still using it, albeit with some slight modifications along the way.

Specifically, I’m using a pair of 120 mm long metric bolts. A nut and a lock washer at the bottom of each bolt keep it firmly attached to the bike. Near the top of the bolt, another nut and a spring washer provide an adjustable “platform” for mounting mirrors.

My first pair of eBay mirrors were “universal”, designed to mount by means of a metal ring and a bolt. So, I was able to mount each ring near the top of the long bolt. Conveniently, this also allowed another degree of freedom, because the ring (and thus the entire mirror assembly) could now be rotated around the bolt.

Note: The threads on readily available bolts don’t come all the way to the heads, where I wanted to attach the mirrors. So, I extended the threads, using a die, elbow grease, and a lot of oil. If you know of a convenient and economical source of fully threaded bolts, let me know and I’ll mention it here…

Details, Take 2

My second pair of eBay mirrors mount by means of a threaded shaft. Building on the approach taken with the first pair of mirrors, I fashioned a pair of steel mezzanine plates. These are rectangular, 1/4” thick, and about 1” by 2” in size. Each plate has holes for the riser bolt and the mirror’s mounting shaft. So, each plate can be rotated into the desired position; the mirror can then be set and tightened up to taste.

My first try at using this capability puts the base of each mirror’s shaft about an inch forward (toward the front of the bike) from the bolt. This keeps it out of the way of the front brake reservoir, etc. I’m hanging the mirrors down from their swivel mounts. This keeps them from extending out to the sides past the handlebars, but the convex lenses still provide excellent visibility.

In the unlikely circumstance that I find some mirrors I like better, I’m now in a position to try them out with very little hassle. The “bolt and mezzanine platform” approach will let me install pretty much any pair of mirrors I want, in just a few minutes. Stay tuned…