Lightweight and durable: plastic-bearing in racing motorbikes

Motorsport on two wheels is characterised by a whole range of different vehicle classes - right down to single-cylinder machines. The limited engine power of these bikes is not a disadvantage if the weight - i.e. the mass to be accelerated - is also greatly reduced. plastic-bearing instead of metal alternatives make an important contribution here. And they offer even more advantages in tough everyday racing conditions.
 
At Krämer Motorcycles (KMC) there is exactly one product to buy: Riding fun on two wheels. To be more precise: a supermono racing bike that is characterised by extreme riding characteristics and has therefore not only been able to win titles in the single-cylinder championship, but can also keep up well in the Supertwin races in the current season. The machine, which is offered under the model designation HKR-EVO2, reaches top speeds of up to 230 km/h. At the Tandragee 100 road race in Northern Ireland, Shaun Anderson achieved an average speed of 100.485 miles/hour (161.715 km/h), making him the first and only racer ever to break the magical 100 miles/hour barrier on a single-cylinder motorbike.
 
Although the company is still relatively young, a lot of development work has already gone into the machine. What began in 2009 as the private project of three friends Christof Henco, Markus Krämer and Nico Rothe - whose initials (HKR) were used in the type designation - to develop their own motorbike purely for motorsport purposes, led to the founding of Krämer Motorcycles in 2014 by Markus Krämer, who had previously worked as a development engineer at KTM. Accordingly, the decision for the central component was not difficult: the single-cylinder KTM 690 LC4 engine served as the drive unit right from the start. The rest of the bike was designed around this, partly using standard parts and partly with components developed in-house.

In motorsport, every gram counts. Metallic bearings increase the weight of the vehicle and therefore affect the overall performance of the vehicle. The bearing points are often subjected to heavy loads due to the tough racing conditions and must therefore be adequately lubricated. This in turn ensures that dirt collects at the bearing points, which can impair the components.

Krämer Motorcycles relies on iglidur® Q and J plain bearings and igubal® rod end, as these offer a lubrication- and maintenance-free solution. They ensure constant functionality as no dirt accumulates at the bearing points. As the plain bearings are made of plastic, their weight is only around a third of the metal bearings previously used. Krämer Motorcycles uses iglidur® bearings in the link, brake and gearshift systems as well as in the footrests. In addition, two igubal® rod ends are used in the foot brake lever. Another advantage of all igus® components: Their service life can be precisely calculated using a free online tool.

KMC takes component after component and endeavours to develop its own products that meet its own requirements instead of standard products. Reduced weight is the top priority here - the less, the better. As the maximum power of a single-cylinder engine is limited, the only way to gain an advantage is to reduce the mass.
 
But simplicity of design is also an issue, because it also determines how easily - and therefore how quickly - a repair can be carried out. In day-to-day racing, this may determine whether you manage to get back on the track in time for the next start. And a certain degree of flexibility is also required. Krämer cites the wheel suspension as an example: "If you want to change the weight distribution, you have to use a different length. Such configuration options must be taken into account from the outset."
 
Another issue is the price. Krämer wants to appeal to a clientele below the fully professional segment. Depending on the configuration, the bikes, which are used exclusively for racing, cost between 15,000 and 25,000 euros. The manufacturer must therefore also ensure that high-quality components are available at a favourable price.

The latest development from the KMC developers is a new link system for the rear swingarm, which connects the rear wheel to the frame via a damper. The shaft of the previous link system contains an inner workings consisting of nine metal parts, which had to be laboriously assembled and lubricated. The new design, which will now be installed in future machines after a year of development, only requires two lubrication-free plastic bearings, which are pressed in and then operated maintenance-free. In addition, the weight is reduced by around a third: from 535 to 355 grams. And last but not least, the price of the components - including the iglidur® Q bearings with flange - is significantly lower than that of the previous design.
 
This application is predestined for the use of bearings from igus®, because large forces occur, but only small rotation angles of up to 10°. This is where the fact that the plastic does not require lubrication pays off. With a similarly simple metal design, you would have to ensure that a complete rotation is achieved, as otherwise there would be no complete surface lubrication. The use of igus® products also corresponds to the principle of simplicity: "Sometimes you just have to press in a plastic bushing where several parts would have to be joined together in a metal version," explains the KMC boss.

Markus Krämer already had his first contact with igus® at his previous employer KTM. There, the products were used in a few niche areas, in the gearstick and steering systems. The final decision in favour of using the plastic components was made at the suggestion of the designer, who had already worked intensively with igus® in bicycle construction. It quickly became apparent that the planned applications could be covered by the igus® standard range. This made the search for an alternative supplier unnecessary.
 
It was easy to start using plastic bearings, as the company was not reliant on customised products. However, Krämer reports that the development of the link system that has now been finalised was time-consuming, as a whole series of tests had to be carried out. The KMC boss explains: "The standard tolerance specifications from igus® were not suitable for our application. A margin of a tenth of a millimetre multiplies here, and then you suddenly feel a movement of one to two millimetres on the rear wheel - unacceptable for a racing machine." In the search for the right tolerances between the hole and shaft, tests had to be carried out to find the right combination. The cooperation with igus® was very good.

Of course, the weight of the machine could be reduced even further, for example by using carbon fibre parts. However, KMC refrains from such extremes in small series production: "That would make the machines almost twice as expensive," explains Krämer. Other racing teams do not have to take this into account when putting together prototypes. However, KMC is not only concerned with racing itself, but also with selling machines. And to do this, an attractive price point must be achieved. Even without these design tricks, he sees himself well ahead in his class in terms of weight: "Definitely in the top 3". Krämer prefers to focus on smaller improvements that are nevertheless noticeable overall. And part of these improvements, in addition to the self-constructed steel frame and a powerful aluminium-based braking system, are the components from igus®.
 
The effect of this combination of low weight and extreme braking power surprises and delights riders in equal measure. While other 80 hp machines are considered to be rather weak-chested, the HKR-EVO2, which weighs just 125 kg, cuts a fine figure with this drive even in a field of significantly more powerful but heavier motorbikes. Strong braking deceleration and precise tracking despite high cornering speeds with extreme lean angles put the racing machine ahead, especially on tracks with tight cornering radii. The result can be seen in Töging: numerous winners' trophies adorn the shelves in the production hall.