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Bike Tale - Posted 20th April 2015
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BMW R45

Mark Holyoake tries a classic airhead BMW, and reckons this small but perfectly formed flat-twin has been especially under-rated...

The road climbed and snaked above the fens in the distance. Riding past a small river where the odd rowing boat bobbed about, the water rippled and glistened and it was really nice to bimble along without a care in the world; the bike beneath purring smoothly.

This BMW comes equipped with a torsion damper which banishes (well almost) the clunk that used to be familiar to Bee Emms, and a surprisingly pleasant and handy gearbox completes the transmission. As with older Beemers, it is beautifully finished. It uses cast rather than wire wheels and has that later style of brake master cylinder on the handlebar, rather than under the tank of Beemers built a little further back in time. In addition (what’s this?), an indicator switch which operates horizontally and isn’t vertically operated with the thumb.

A largish petrol tank gives around 240 miles before a stop to refuel – typical BMW fare. The single-walled exhaust pipes are blueing slightly, where other manufactures might use double skins. The silencers flatten out along a slightly rakish angle to allow the customary panniers to be mounted. This twin uses long-ish travel suspension both front and rear, with built-in handles to alter the pre-load. Two discs up front provide ample stopping power and no worries for the pilot.

BMW R45

Impressions of the BMW: comfort and no first aid kit under the front of the saddle. A joyous ability to flick left and right and not ground the cylinders. A nice neutral feel with the bike feeling it can be flung about: lovely.

Getting back to the fens we encounter a long straight. It’s bumpy, allegedly used by BRM to test cars back in the day, and it puts the BM’s suspension to a more severe test. However, wheels stayed in line and there’s no need for a steering damper, the forks and shocks however having a decent workout. The rider, cushioned (a bit) from the chaos.

If today’s ‘comfy speed’ is 55mph, then touching the ton on an autobahn should be no problem. The bulk of torque is produced above 3000rpm giving the bike the ability to cruise at 5000rpm. Then revving up to about 6000 sees 80mph, and on A-roads 5500rpm (75 mph) makes for a pleasant ride. With the carburettors set properly, this bike could average 60mpg if kept below 70mph, 55mpg below 80mph, and 50mpg when / if ridden with abandon.

So it’s most definitely a finely balanced twin, but which one is it?

This is that oddball from BMW’s back catalogue, their smallest twin, the BMW R45.

BMW R45
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The R45 uses most of the same bits as the larger models, even the crankshaft having the same main bearings, etc, and being made from the same forging. The big ends were ground on different centres to give the shorter stroke. For some reason the valve stems are only 7mm rather than 9mm, hence the problems on pre-81 engines with valve heads breaking off. Post 1981 the head/stem weld was moved upwards, to within the guide.

Mike Fishwick, BMW Techy Guru, recalled that the only problem he had was that when going from his KRS or RS he had to make a conscious effort to change up at about 4000rpm when the R45’s engine was warm, rather than the 2000rpm on the large engines. This is probably why media hacks regarded the R45 as being underpowered, comparing it to the big boxers rather than reporting on the R45 as a 500cc twin. On the same subject (a bit of folk-lore) a friend of Mike’s is a very good rider and usually rode a Guzzi Monza. When loaned an R45, the Monza-owner admitted that it went better, handled better, and stopped better (with twin front discs). So much for the superiority of the Italians!

The R45 appears to be capable of cruising two-up at 80mph all day. Some other 35hp twins from the 1960s to 1980s might not quite be so happy at being run like that...

BMW R45

So there, the R45 is a good go-anywhere, do-anything machine. An under-rated twin? Probably! However, my personal opinion might be influenced by the type of bike I enjoy riding. I also liked the Moto Guzzi Nuovo Falcone, which likewise tended to get a battering in the press for being overweight with poor performance. I found it charming, robust and well made. It’s just my knee didn’t enjoy the starting experience.

The R45 ‘owns’ the NF in terms of performance although the BM is missing the Guzzi’s wondrous flywheel effect, and maybe it’s not quite so strongly engineered. Yet the R45 was built in a time when BMW clung on to the ‘quality / engineered’ ethos rather than an ‘accountant driven’ process. That didn’t stop the press giving it a hard time when new.

So maybe my conclusion should be that I’m simply a sucker for a slow, old, lost cause of a bike?


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