Contrail MGN full-suspension bike from Bergamont is a top mountain bike model. The bike uses innovative technology, such as butted frame tubes with various wall thicknesses as well as carbon frame components to deliver Olympic-winning performances. Light polymer plain bearings from igus are also used to handle the severe stresses of the rear suspension.
Full suspension bikes – also known as ‘fully’ – with a spring-mounted rear wheel are found to be the best by anyone who rides mountain bikes for fun and professionally. They give a far more comfortable ride and are ultimately faster, because the rider has to respond less to uneven ground. The adjustment of the suspension must be good and tight in order to provide the comfort and performance desired. They must be set up to absorb quick jolts well, therefore not endangering the stability of the rear suspension, and the whole system must also be ‘drive-neutral’ with motion of the suspension not being transferred to the pedals.
The Contrail MGN model, designed by graduate engineer and product manager Thomas Marquardt at Bergamont, features supported single linkage rear suspension with a bell crank on the frame. Known as a ‘Top Fully’ in the trail bike category, they are for athletes who both win marathons and also want to enjoy cycling for fun.
Bergamont originally used ball bearings for all the bearing points of its ‘Fullys’. Marquardt says: “At the two front pivot points, at the connection between the swingarm and the frame, we used deep groove ball bearings. This is because the bearings here have to execute a relatively large swivel movement.” However, Bergamont has taken a new approach for the Contrail MGN and is using a plain bearing at the rear joint, on the rear axle.
There are good reasons for this, the most important being lateral stiffness. A plain bearing offers a much larger contact area than a roller bearing. Marquardt explains: “Even with very severe stresses and large lateral forces, nothing wobbles.” The plain bearings will perform very well with the high-pressure loading at this bearing point. He notes: “The pressure is also very well distributed over the larger area.”
Tribologically optimised polymer materials
Bergamont needed advice in selecting the optimal bearing material, and its tests with plain bearings on the suspension joint were supported by igus, who offers 10,200 items, including 35 different tribologically optimised polymer materials. The first tests were performed with iglidur G because this universal material offers the broadest range of applications at an economical cost. However, as the wheels often run through streams and puddles, and they are often cleaned after use with a garden hose or even a pressure washer, iglidur J proved to give a higher performance with greater dimensional stability when wet. Thomas Marquardt says: “These conditions are no problem for polymer plain bearings.”
The self-lubricating iglidur polymer plain bearings can expect a long and reliable service life and the feedback from bike owners was 100 per cent positive. The torsional stiffness of the wheel is very good and the suspension responds very quickly. The careful design of the bearing point certainly contributes to this. The innovative use of plain bearings is one of many factors that proves Bergamont’s high-tech claim for mountain bikes and trail bikes. Other design features include butted tubes with varying wall thicknesses, which contribute to the light weight of only 10.8kg. The fork is fitted with a carbon crown; the dropouts are 3D forged.
The bikes deliver world-class performance: the Olympic gold medallist in Beijing 2008, Sabine Spitz’s bike, had iglidur plain bearings in a sensitive suspension fork. The polymer components stood up to the constant impacts, edge loads, and dirt on the difficult and spectacular course at the Chinese Laoshan Velodrome. At the 2004 Athens Olympics, iglidur bearings were also on the winners’ podium. Light and wear-resistant, they were built into the guide rollers of the derailleurs.
For further information about igus bearings visit www.igus.co.uk.