Plastic bearings in racing motorcycles - To victory with ease

Two-wheel motorsport has a whole range of different vehicle classes - down to single-cylinder machines. The limited engine power of these bikes is not a disadvantage, if the weight - namely, the mass to be accelerated - is also reduced considerably. Instead of metallic alternatives, plastic bearings make an important contribution here. And they display even more advantages in the tough everyday racing environment.
 
At Krämer Motorcycles (KMC) there is exactly one product to buy: riding pleasure on two wheels. More precisely: a Supermono racing bike, which by virtue of its extreme riding characteristics not only won the title in the single-cylinder championship, but can keep up well in the current season in the Super Twin race. The machine, offered under the model name HKR-EVO2, has a top speed of 230km/h. In the Northern Irish road race Tandragee 100, Shaun Anderson achieved an average speed of 100.485 miles/hour (161.715km/h) and became the first and only racer ever to surpass the magical 100-miles/hour mark on a single-cylinder motorcycle.
 
Although the company is still relatively young, a lot of development work has gone into the machine. It began in 2009 as a private project of three friends, Christof Henco, Markus Krämer and Nico Rothe - whose initial letters (HKR) denoted the type designation - to develop their own motorcycle purely for motorsport purposes. This led to the founding of Krämer Motorcycles in 2014 by Markus Krämer, who previously worked as a development engineer at KTM. Accordingly, the decision for the central component was not difficult: the single-cylinder engine KTM 690 LC4 served as a drive unit from the beginning. Around this was built the rest of the bike, partly with standard parts and partly with self-developed components.

Markus Krämer, CEO and founder of KMC, and the Supermono bike HKR-EVO2.

Problem

In motor sport every gram counts. Metallic bearings cause the weight of the vehicle to increase and thus affect the overall performance of the vehicle. The bearing points are often heavily stressed by the tough racing conditions and must therefore be adequately lubricated. This in turn ensures that dirt collects at the bearing points, which can affect the components.   

Solution

Krämer Motorcycles relies on iglidur Q and J plain bearings and igubal rod end bearings, as they offer a lubrication-free and maintenance-free solution . They ensure constant functionality as no dirt accumulates at the bearing points. Since the plain bearings are made of plastic, their weight is only about a third of that of previously used metallic bearings.  Krämer Motorcycles relies on iglidur plain bearing among others in the link, brake and shift system as well as in the footrests .  Additionally, two igubal rod end bearings are used in the foot brake lever.  Another advantage of all igus components: Their service life can be precisely calculated with the help of free online tools.  

Weight and price are decisive

KMC looks at each and every component and tries to come up with in-house developments that meet their own requirements instead of the standard products. Reduced weight is of prime importance - the less, the better. Since the maximum power of a single-cylinder engine is limited, the only way to secure an advantage is to reduce the mass.
 
The simplicity in the design is also an issue, because it also depends on how easy - and thus, how fast - it is to carry out a repair. In the world of racing, this is crucial to be fit and ready for the next race. And a certain flexibility also has to be granted. Kramer points out the suspension as an example: "If you want to change the weight distribution, then you have to use a different length here. Such configuration options must be considered from the beginning. “
 
Another topic is the price. Krämer wants to address a clientele below the fully professional segment. Depending on the configuration, the bikes that are exclusively used for racing cost € 15,000 to 25,000. Therefore, the manufacturer must also pay attention to obtain high-quality components at a cost-effective price.

The footrests and the brake system use different igus components. The rod ends here are not from igus.

Plastic instead of stainless steel

The latest development of the KMC designers is a new link system for the rear swinging arm, which connects the rear wheel with the frame via a damper. The shaft of the previous link system contained an interior with nine metal parts, which had to be laboriously assembled and lubricated. The new design, which will now be installed in the future machines after one year of development, only needs two press-fit lubrication-free plastic bearings and can be operated maintenance-free. In addition, the weight is reduced by about a third: from 535 to 355 grams. And last but not least, the price of the components - including the iglidur Q flange bearings - is significantly lower than that of the previous design.
 
This application is predestined for the use of bearings of the company igus, because great forces occur, but only small angles of rotation of up to 10°. In this regard, it is an additional benefit that the plastics get along without lubrication. In a similarly simple design in metal version, a complete revolution would have to be achieved in order to ensure a complete surface lubrication. The use of igus products also complies with the principle of simplicity: "Instead of having one press-fit plastic bushing, several parts would have to be put together in the metal version", explains the KMC boss.

The link helps to absorb shocks on the rear wheel.

Versatile use

Wide range meets every need

Markus Krämer already had his initial contacts with igus during his time with his previous employer KTM. There, the products were used in a few niche areas, in the shifting system and the steering. The final impetus for the use of the plastic components came from the design engineer, who had already worked intensively with igus in bicycle construction. It quickly became clear that the planned applications could be covered by the igus standard range. Thus, the search for an alternative provider was unnecessary.
 
Starting to use plastic bearings was easy, since one did not have to rely on custom-made products. However, the development had been complicated in the now completed link system, says Krämer, because one had to perform a whole series of tests. The KMC boss explains: "The standard data on tolerance from igus did not fit our application. A clearance of a tenth of a millimetre multiplies here, and then you suddenly feel a movement of one to two millimetres at the rear wheel, which is unacceptable in a racing machine." Therefore, in the search for the correct tolerances between hole and shaft, one needs to approach the right combination through tests. With igus, the collaborative work went very well.

The newly developed link system with iglidur plain bearings is a simple and lightweight design.

Ride on the razor blade

Of course you could reduce the weight of the machine even further, for example, by the use of carbon fibre parts. But KMC abstains from such extremes in the small series: "That would make the machines almost twice as expensive," explains Krämer. Other racing teams need not pay attention to it when assembling prototypes. But KMC is not just about racing, but selling machines as well. And to do that, an attractive price point has to be reached. Even without these design gimmicks, it sees itself far ahead in its class in the weight comparison: "In any case, among the top 3". Krämer prefers to rely on smaller improvements, which nevertheless make themselves noticeable as a whole. Besides the self-designed steel frame and a powerful, aluminium-based braking system, a part of these improvements are just the components of igus.
 
The effect of this combination of lightweight body and extreme braking power surprises and excites riders alike. Whereas other 80-horsepower machines are regarded as underpowered, the HKR-EVO2 weighing only 125kg cuts a good figure with this drive against much more powerful, but heavier motorcycles in the field. Strong braking deceleration and precise track guiding despite high cornering speeds with extreme riding positions bring the racing machine forward, especially on stretches with tight bends. The result can be seen in Töging: numerous winners' cups decorate the shelves in the production hall.

In the uninstalled state you can see the igus plain bearing in this brake lever.

On the road to victory

Two new trophies were added in 2018 as well. This also garnered the respect of many motorsport fans who were able to see for themselves the nimble riding style of the Krämer machines at the racetracks in Europe and the USA. Accordingly, the business is developing well. Whereas only 14 machines were sold in 2015, the target for 2018 is to sell about 50 to 75 machines. And then, of course, a few more victories - perhaps even on home soil. While the races of the Super Twin class are all held in the UK this year, the Super Mono Championship also comes to Germany. At the Motorsport Arena Oschersleben, KMC will be back atthe lineup of the FIM Europe Supermono Cup on the 25th and 26th of August.

Another plastic bearing is installed in the shifting system.