What do the “bumometer” and the roll/pitch motion have in common? Quite clearly: both are key criteria used by Berthold Merkle and Bernd Gutmann to perfectly tune the driving comfort of every Setra bus and coach to the relevant fields of application. To be more precise, they select the optimum shock absorbers using these standards. Because these have a considerable influence on the feeling of comfort – for the passengers, but also for the driver.

Test engineer Berthold Merkle and technician Bernd Gutmann climb aboard the Setra ComfortClass S 511 HD for a test drive. At first glance the vehicle appears to be already full with passengers. Taking a closer look behind, however, you can see that water-filled dummies are simulating the travellers here. Instead of the usual suitcases, bags of sand are placed in the vehicle’s belly – with good reason, as Bernd Gutmann explains: “The shock absorbers have to cushion the load, which is why we do our tests with different vehicle loads, in other words empty, partly and fully loaded. When it comes to road conditions, we look for characteristic routes for the purpose of the vehicle in order to also test the worst case, for example cobblestones or motorways with offset flagstones.” For these measurements, the “bumometer” is used. The special sensitivity in the gluteal muscles which decides on the right shock absorbers.

Then it all begins. The Setra sets off whilst the two experts look through the windscreen as though spellbound. The question is: is the bus pitching severely, rolling or is it bumpy? “If you sit in the back row, look forward and the shock absorbers are too soft, then the front goes up and down and you lose the horizon. This ‘pitching’ makes many passengers feel ill,” says Berthold Merkle.

Dampers that are too firm impair the passengers’ sense of well-being; ones that are too soft impair the driver’s handling and hence the feeling of safety. “If we make the shock absorbers a bit firmer, tune them to the vehicle, the driver has to make fewer steering corrections to hold his lane,” explains Berthold Merkle. “On the test drives, we can tell very soon whether the bus needs more driving comfort or more stability.” It is precisely this balancing act between comfort and stability, a compromise of the two, which both men look for when designing the dampers.

It is not possible to learn this special feel. A certain basic feeling should already be inherent. Both experts agree here. Added to this, however, is plenty of experience: at least three years with five to ten tunings a year. This time is necessary to know approximately what details you have to look out for so that the vehicles run well when they go into production. Because that is the point and purpose of these tests. “We want to tune the vehicle so that our customers, and their passengers, feel good all round,” emphasises Bernd Gutmann. “We make a great deal of effort here to set our products apart in the international market. Not many competitors do these workshops.”

The experts are therefore fully conversant with the road conditions in the various countries. During winter testing, for example, the team head to Scandinavia for four weeks. They cover around 5,000 kilometres in the process. “You have to live for this job. If you don’t like riding buses, don’t like travelling and shy away from extremes,you will never get the right feeling,” says Berthold Merkle. Bernd Gutmann adds: “An affinity with the product simply goes with the job. For us and our colleagues, this is precisely the case. The passion for our buses is there in everyone to a large degree. In this way we even overcome extraordinary trials together, for example extreme weather conditions.”