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BMW F650CS Tech Article

25 Mar 2015 | စာရေးသူ: | ဟာ Off comments အပေါ် BMW F650CS Tech Article

BMW F650CSit’s Scarving time

Technical Article by Dick Henneman

A funky supermotard evolution of the F650ST, which itself was a street development of the F650. Now on 17 inch alloys front and rear (old was 18F/17R spoked), which allows it to be shod with wider and stickier sportsbike rubber. The engine is a BMW development of the old 650 Rotax unit and the new cylinder head has lost one exhaust port and a spark plug, and gained fuel injection.

Double overhead cams and four valves are retained and the compression ratio is up to 11.5:1 from 9.7:1. The result is a couple more peak horsepower at 6,500rpm and a little more torque some 300 rpm up the rev range at 5,500 rpm ပါ.

The biggest visual changes are the toothed belt drive to the rear-wheel, which is now supported on a single-sided swingarm, the projector headlights on a more aggressive looking front fairing and the “multi-purpose” compartment on top of where the tank normally is. The slightly smaller fuel tank is now under the rider’s seat, and in fact takes up virtually every last cc of the underseat area. The bottom of it even forms the rear wheel undertray.

But as the claimed fuel consumption is down by 25%, the range on a full tank should be about the same. Under all the plastic there’s a twin-beam steel top frame replacing the old spine one, but the oil for the dry-sumped engine is still stored in the frame tubes up by the headstock. This means a short life for the head races, which run dry when the heat from the oil melts the grease in the bearings.

Front suspension is non-adjustable as before, but the CS has lost the rear ride height adjuster of the ST, which was very useful when the bike was used two-up or carrying a load. In line with its greater “street orientation”, suspension travel is reduced, as is the ground clearance, so getting the pegs down should be a lot easier. Wheelbase is up by 25mm to 1,493mm, trail is down by 14mm and the bike has shed a couple of kilos from it’s already light weight predecessor, probably by getting rid of the centre stand.

သို့သျောလညျး, it would be a mistake to think of this as a development of the 650ST; it is in fact an all-new bike which just happens to be powered by a single cylinder 4-stroke motor with the same bore and stroke as the ST. BMW’s Marketing department have also come up with a new name for the bike, and called it “The Scarver”. Riding the CS is described as “Scarving”, whatever that is, although it will probably appeal to the active youth market that the bike is aimed at.

There’s a whole range of goodies available for the bike, from soft luggage and sound systems to bolt on carbon fibre and stainless steel bits, as well as a whole line of clothing for on and off bike use. And if that’s not enough you can also do a “mix match” type exercise of different coloured components to select the look of the bike that you buy.

Sitting on the bike for the first time, you’re immediately struck by how low the bike feels, and although the seat height is only down 5mm on the ST’s 785mm, it feels much more than this. Ahead of you there’s this strange tray where the tank filler normally sits, and it looks as though it could hold a substantial lake if the bike is left out in the rain, as there’s no drain holes in it.

If not dried out first, this will immediately transfer itself to the rider’s crotch as the clutch is let out, so all prospective owners would be advised to carry a sponge with them at all times! Nice wide bars have all the usual switches in all the usual places (thankfully BM have refrained from fitting their “unique” indicator switches), and there’s even a three-position switch for the heated grips which were an option fitted to this bike.

Strangely, there’s no light switch, as these now come on automatically with the ignition, in line with new legislation that comes into effect for all vehicles later this year. The analogue speedo and rev counter are grouped around the usual ‘idiot lights’, including one for low fuel and one for the ABS option that was fitted to the test bike. There’s also an LCD clock and an LCD odometer, which can be switched between total miles and a trip function.

Switch on the ignition and press the starter, and after a couple of seemingly lethargic rumbles, the big single fires up. As it’s fuel-injected, there’s no choke and the bike will pull away smoothly from cold. On the move, the lowered centre of gravity from the re-positioned fuel tank makes itself felt with good low speed stability and easy direction changes.

In fact this is a very easy bike to ride, and surprisingly for a single, there is very little vibration through the pegs or bars at any engine speed, in spite of the fact that the old rubber bar-mounts of the ST have been replaced with solid ones. The five-speed gearbox is positive, if somewhat agricultural compared to a Japanese one, and there were no false neutrals on the test bike.

From rest, first gear selects with a solid clunk, and as it high geared it’s best to short-shift to second as soon as possible. The remaining ratios are reasonably spaced and the engine can be revved-out to get the maximum acceleration. In fact the engine pulls strongly right through to the 7,500 rpm limiter in all gears, whereas its Rotax predecessor got all breathless around 6,500 rpm ပါ.

The fuel injection is good, with only a slight tendency to “hunt” on small throttle openings. Slightly more disconcerting, until I got used to it anyway, was a rather strange ‘two-stage ramp-effect’ when the throttle was opened. By this I mean that the first movement of the throttle produced a very gentle increase in engine speed and then, as if a switch had been closed, the engine got onto the power hard as you continued to open the throttle.

BMW F650CS

This happened in all gears and irrespective of the engine speed. It was as if the engine management was checking to see if you really wanted to accelerate that hard, and then when it found the throttle was still being opened, said “OK – Lets Go!” The old carburetted engine had a much sharper throttle response, but felt much less refined especially around 4,000 revs, and also suffered from driveline snatch at low revs, something completely absent from the CS and probably due to a combination of the fuel injection and the belt drive.

The suspension is fairly soft front and rear although well damped, and the ride is excellent with the front end only getting a little vague at highly illegal speeds. The bike sometimes got a little out of shape if you were pushing it hard through long sweepers and encountered some unexpected bumps and ripples. This happened a couple of times at around 90-95 with the throttle pinned to the stop, and the bike shimmied gently as the suspension fought to keep up with the inputs it was receiving.

But it was nothing alarming and the whole thing stayed on line through the corner, helped no doubt by the Dunlop D207s, which gave good grip and feedback. The brakes are more than adequate for the performance of the bike, although they lacked the bite and feel of a sportsbike. But as the CS had only done 1,200 မိုင်, the pads and discs may not have fully bedded-in.

The test bike had the £345 ABS option fitted, which I didn’t get the chance to use, but it didn’t interfere with normal braking and it was nice to know it was there if needed.

The riding position is relaxed, with little body weight being taken through the arms, and the wide bars give good control, especially at low speed through traffic. The generously padded wide seat gave good support, and even after 2 hours in the saddle there were no twinges or aches.The small fairing does a surprisingly good job of deflecting the air over rider, and even with the speedo showing 110mph there was little upper body pressure from the airflow.

But like all unfaired bikes, you do get the usual buffeting from other vehicles when following at speed. The mirrors were good and solid up to around 70-75 တစ်နာရီမိုင်, and then got a little blurred but still quite readable. သို့သျောလညျး, on the test bike the right hand mirror head folded back at 95 mph and the pivot couldn’t be tightened to stop this happening.

Conclusion

In spite of its somewhat unusual looks, BMW have come up with an excellent bike in the 650CS. This is a machine that can be a good first bike for the new rider, as it can be both forgiving when things go wrong and rewarding when you get things right; and the more experienced rider will also enjoy the handling and performance without having to think too much about their licence. And if that’s not enough, this is a bike that can commute, tour, and blast the back roads on a warm summer day.

With BMW now building the bike in-house instead of farming out production to the Italians, the quality control problems that occurred with some of the earlier 650s should be a thing of the past. Which in turn means that this could be a bike that could be ridden all year round. But only time will tell.

BMW F650CS
BMW F650CS
BMW F650CS


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