BMW’s frame tech explained
New S1000RR’s frame is revolutionary, too
It might be the new ‘Shift Cam’ variable valve-timing technology that is making the headlines, but there is more to the 2019 S1000RR than a new motor. It also includes a new frame and swingarm that is lighter and more flexible than before in a bid to make the bike easier and more forgiving to ride.
Stressed member
“The main aim was to develop further enhanced riding dynamics as well significantly reducing weight, compared to the predecessor model. We were able to meet this target by means of the new main frame: the engine is now much more closely integrated as a load-bearing element, and there are a whole range of optimised details,” explained Marcus Mund, Project Engineer Suspension. Dubbed the ‘Flex Frame’, the concept behind the frame is similar to before; a structure of four cast aluminium elements welded together using the engine as a stressed member and integrated at a 32-degree tilt. But in order to save weight, the top tubes, steering head and engine mounts are reduced in mass, relying on the engine more for an increased load-bearing function but with special effort for the load paths to the engine being as short as possible. The new frame also benefits from being as narrow as possible, reducing the width of the bike by up to 30mm. All of this also reduces the frame weight by 1.3kg, which contributes to the claimed 11kg weight reduction of the new bike.
Swinging low
The S1000RR also boasts a new swingarm now with underslung bracing. Superbike racing S1000RRs (which are allowed aftermarket swingers) have been using under-slung bracing for years and there are a number of advantages to it. Firstly, when it comes to packaging, there is more space below the swingarm rather than above it and this means there is more flexibility with bracing design. Secondly, the way they flex allows a reduction of lateral tyre contact patch movement during flex. The bracing below has also allowed more freedom in the placement of the damper and spring unit, which can now be further away from the engine unit for reduced
heat transfer. Amazingly, despite its complex structure, the new S1000RR’s swingarm is cast in one single piece before being machined for the chain adjusters and mounting points. It’s also 300g lighter than the previous bike’s swingarm.
Angle of dangle
BMW have also played with the new bike’s geometry, lengthening the wheelbase by 9mm to 1411mm (Superstock racers have traditionally pulled the wheel back as far as it can go for the same effect) in a bid to aid stability. That extra wheelbase has allowed tighter, more extreme steering geometry as well, being 0.4 degrees steeper at 23.1 degrees while trail has been reduced to 93.9mm. All of which points to a machine that is lighter, more nimble and more stable all at the same time.