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Period Roadtests

BMW R100RS
BMWR100RS

BMWR100RS

When the RIGORS BMW was announced, in September of 1976, it looked like no other BMW before it; indeed, it was very different from every other motor cycle on the road. The obvious difference is the big Bee Emm's fairing, which is wind-tunnel developed. It cuts down drag, reduces lift at high speed, makes the bike more stable in cross winds and, incidentally, looks very smart.

Internally, the obvious improvement over the 100's predecessor, the R90S, is the extra capacity, which boosts the total displacement to 980cc. In RS trim, the flat-twin unit produces 70bhp at 7250rpm and an impressive 55.71b ft at 5500rpm. More importantly. the torque curve is particularly flat over a large part of the rev range. On the road, this means that acceleration is smooth and quick and virtually constant. whereas a large two-stroke bike, such as the Kawasaki 750. with a 'peaky' engine, will have almost negative acceleration should the engine speed drop below a very narrow and critical range.

The BMW. however, is a high-speed tourer and is not designed for race-style getaways, even though its sub-14-second standing-start quarter-mile time is quick by any standards.

The high, 5001b machine takes some getting used to. especially when negotiating town traffic, its weight and considerable proportions making progress more of the 'follow the stream' kind rather than 'find the gap.' Blipping the throttle at a standstill produces the famous BMW trait of the torque reaction tipping the bike to the rider's right. Any time the bike does tip to an angle of more than a few degrees, one has a struggle to keep it upright, the fairly high seat not helping things, especially if one is shorter than 5ft lOin. Once on the move, however, one quickly forgets about the weight and the movement and the machine is transformed into an extremely smooth and efficient tourer.

Acceleration is totally drama free: the power is put down exceedingly well and there is absolutely no hint of control loss, even when blistering away slipping the delightfully light clutch.

The gearchange is far better than on previous machines although it still suffers from the 'shaft-drive clunk'. Two large, cross-drilled discs at the front stop the bike well in any weather, but the large rear drum seems less efficient.

As for the handling, one does not throw a big BMW around, it just corners well on its own. Even at very high speeds, the machine banks over without any of the fuss and twichiness that plagues machines of lesser breeding.

It is when one is travelling at speed that the fairing is noticed: crouching slightly is all that is needed to keep out of the airstream and there is hardley any trace of turbulence at all. In fact, when it is raining the rider should keep completely dry as long as the speed is kept above, say, 25mph.

Accentuating its touring capabilities the bike can return up to 50mpg and, with a 5 1/2 gallon fuel tank, gives a possible range of over 260 miles between refills. However, two up touring on the banana sports seat is out except for the very closest of friends, perhaps the optional dual seat is the better proposition.

Engine
Air-cooled flat-twin four-stroke. 94mm (3.7in) bore x 70.6mm (2.78in) stroke = 980cc (59.8cu in).
Maximum power (DIN) 70bhp at 7250rpm:
maximum torque (DIN) 55.71b ft. Aluminium-alloy cylinder barrels and heads.
Compression ratio 9.5: 1. 2 main bearings. 2 valves per cylinder operated, via pushrods and rockers, by a single central camshaft.
Two Bing constant-vacuum carburettors.

Transmission
Single-dry-plate clutch and five-speed gearbox with left-foot change
ratio: 1st 4.40, 2nd 2.86, 3rd 2.09. 4th 1.67, 5th 1.50:1.
Shaft and hypoidbevel final drive to rear wheel ratio 3:1.

Suspension
Front-teleseopie fork with coil springs, hydraulic dampers and steering damper, rear longitudinal rocker armwith progressive-action spring struts, three-position setting for rear springs.

Brakes
Twin cross-drilled discs, front and drum, rear.

Wheels and tyres
3.25m x 18m front, 4in x I8in rear. Spoked wheels standard (light-alloy optional).

Weight
5001h (227kg).

Tank capacity
5.25gals (24.15 litres).

Seating
Single sports saddle (dual saddle optional).

Performance
Maximum speed 125mph. Standing-start quarter mile 13.6secs.
Fuel consumption 40mpg.

If you need work done on your classic machine, from basic service to full rebuilds, contact me, I can help.

Period Roadtests

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