BMW and their contribution to the world of motorbike suspension
Intro by Chris –
Here then is the Suspension Bible : Motorcycle edition.
Oh – a little note – the reason I switch back and forth between motorbike and motorcycle is simply an internet thing. I’m trying to make the page more friendly to search engines for people looking for both words : motorbike and motorcycle. That’s all…..
Copyright ©1994 – 2008 Christopher J Longhurst. All Rights Reserved
Bayerische Motoren Werke: those teutonic Germans and their incessant need to be at the pinnacle of engineering excellence. BMW are responsible for a lot of developments in motorbike suspension – not just the quirky ones. The first hydraulically dampened telescopic fork on a production motorcycle (1937), the longitudinal swinging arm (’50s and ’60s), and the long-stroke high-comfort telescopic fork (1970). Because of this, I’ve given them an entire section to try to explain some of their innovations for which we should all be thankful.
Well perhaps not all, but those riders who have chosen BMW as their steed of choice will know that their bikes have what could best be described as some pretty funky and unconventional suspension systems. BMW, it seems, are never quite happy with the status quo. Why use an existing design when it could be bettered? Why settle for DVD when you can have Blu-Ray? Just because a particular type of suspension system is favoured by the Japanese, and sold on hundreds of thousands of motorbikes every year doesn’t necessarily mean that its the best option. At least not in the eyes of the Germans.
BMW have long been known for their ability to cast scorn the accepted way of things, and pursue other, better methods of achieving the same result. Whether their suspension systems for their bikes actually are better or not I suppose is open to debate. Having ridden and owned a BMW with telelever suspension, I can’t understand why its not used on all bikes. Conversely, bullet bike riders will look at a BMW and see nothing but excess weight. You can be certain of one thing with BMW suspension systems: they’re different. Very different. So lets start at the back and work forwards.
In 1980, BMW introduced the world to the monolever suspension system on the back end of their R80GS big dirt bike. Little did anyone know at the time that it was a sign of the radical design changes to come. Most BMW bikes, modern ones anyway, have shaft drive, so its a given on a beemer that one side of the rear suspension is going to be pretty beefy because it has to house the driveshaft and ultimately the rear drive. BMW capitalised on this and with the monolever, they created a single-sided suspension system, much like the Yamaha monoshock, but the shock / strut unit was mounted to one side of the bike, rather than in the centre. The driveshaft ran down the inside of the single-sided swingarm and into the rear drive. This design helped eliminate the need for beefier engineering at the front of the swingarm which would have been needed to resist the torsional load of having the wheel mounted to a single-sided swingarm.
Rear Paralever Suspension – first generation
In 1987, BMW improved on their design and introduced the paralever suspension system on the back end of the new R100GS, a system which found its way on to their K1 sports bike too.
(Note : This is an improvement of a suspension system originally fitted to the Magni Sfida called Parallelogramo. It was also available as a kit for Moto Guzzis in the 80s. Parallelogramo itself is a derivative of a prototype suspension of the same type shown on the MV Agusta 500 in 1950)
Paralever uses the same basic principle as monolever but adds a lower control arm to the mix and an extra pivot point between the main swingarm and the rear drive. The effect is that the old pivoting swingarm now becomes part of a skewing parallelogram system – in fact a geometric double wishbone system just like in a car. This added lateral stiffness to the suspension, but it also kept the rear drive at the same orientation relative to the rest of the bike. Because of the extra link at the rear drive, the strut / shock unit was turned over so that it was “the right way up”, and it was still mounted to one side of the bike. Because the whole system now acts as a double swingarm, it substantially reduces the change of load response of the driveshaft. Using this type of suspension was also the impetus for BMW to change to using the engine as an integral stressed member of the frame, which allowed the swingarm and suspension components to be bolted directly to it.
Suspension – second generation
Suspension – second generation
In 1993, the second generation paralever system appeared on the R1100GS. The basic design was the same as the original paralever except that the strut/shock unit was moved away from the side of the bike and on to the centreline, bringing it more in line with the monoshock type system. It also gained a remote preload adjuster and spring plate height adjuster. This new paralever was made of aluminium instead of steel so it was lighter than the original whilst maintaining the strength needed for the single-sided shaft drive system.
Suspension – third generation
Skip forward ten years to 2004 – which tells you how good the paralever II was that its design didn’t change in nearly a decade. The third generation paralever appeared in the new R1200GS. This design is similar but at the same time noticably different to its predecessor, and at the time of writing is now the current BMW rear suspension of choice. The control arm was moved above the shaft drive from underneath, and the rear drive was changed to have a hole through the middle of it to save weight. The unsprung weight of the latest generation paralever is considerably lighter than its predecessors. That’s not to say that it couldn’t still be used as a substantial bludgeoning weapon if you got it off the bike, but in engineering terms, it has slimmed down considerably.
Front Telelever Suspension
In 1993, when paralever II appeared on the R1100GS, BMW also introduced their new telelever front end suspension system. The problem with traditional telescopic fork suspension is that all the forces acting on the front of the bike are transmitted to the handlebars, and thus the rider. Some people think this is A Good Thing – it keeps the rider “informed” as to what is going on. Others argue that it is a necessary evil and that telescopic forks are an unfortunate accident of history (see the section on forks above – it’s the same reason we got VHS when Betamax was the better system). BMW fell squarely into the second camp, and developed telelever as a method of separating the braking and suspension forces from the steering force. With telelever, there is now a single strut/shock unit in place of the combined spring/shock functions of telescopic forks. Telelever still has front forks, but their primary function now is to make a stiff frame for the front wheel to sit in, and to allow the rider to steer the bike (which is always useful). The strut/shock unit is connected to a wishbone which itself is connected to the frame of the bike at the back via a yoke, and to the crossmember of the forks at the front using a ball joint. When you hit a bump with telelever, the suspension forces are transmitted through the ball joint, across the wishbone and up through the strut / shock unit into the frame of the bike. One of the biggest advantages of this system is that you don’t need to engineer an anti-dive system into the forks. The design of the Telelever effectively reduces fork flex under braking to near zero which in turn reduces dive under braking. Another benefit is that the forces acting on the steering head bearings are dramatically reduced. In fact with telelever, as a rider you have to get used to the concept of braking without the bike diving at the front. It’s really quite unique.
Front Duolever Suspension
Never being satisfied with resting on their laurels, by 2004 BMW decided that telelever was yesterday’s news, and introduced duolever on the front of their first inline-four sports tourer – the K1200S. I’m not sure, but I think some of the BMW engineers might have discovered suspension nirvana with this system as they now finally have double-wishbone type suspension both front and rear. Duolever is an evolution of Norman Hossack’s double wishbone / parallelogram suspension, which is why its sometimes referred to as Hossack Suspension (see below). The idea itself has been around since Hossack modified a Honda XL500 in 1979. In the early 90’s he modified a BMW K100RS, and whilst it never really caught on in England, German engineers understood the idea instantly. Like the rear paralever, its geometrically a double wishbone system. As with telelever, in duolever the pivoting links and springs are not steered. But with duolever, the physical link from the handlebars to the suspension is radically different, involving a hinged link. If you look at the image here, you’ll see the front suspension is completely independent of the steering, with the two only being connected by the hinged link up top. (That link is simply used for turning the fork assembly and provides no structural support or strength). Hover your mouse over the image for a close-up of the system. With the combination of paralever III on the rear, and duolever at the front, sitting on and riding a K1200S is unlike riding any other type of motorcycle. Whilst it may technically be the current pinnacle of motorbike suspension design, BMW have created a system which has divided riders into the love/hate camps.