2.3. Measurements
All measurements described below have been done on short laps consisting of multiple types of
pavement. Three specific experiments have been done, in each of the three experiments one of the
variables has been changed while keeping the others constant. In the first test the tire pressure has been
varied. Four pressure levels have been tested: 5, 6, 7 and 8 bar. The second test was done on the mountain
bike; in this test the speed was varied. The first 3 laps were ridden with a cruise speed of 18 km/h, the
following laps with 25km/h and 32 km/h, respectively. During all 9 laps the Manitou suspension fork was
locked. Three additional laps were ridden at 25 km/h, but with the fork unlocked. During the third
experiment different wheelsets were used. Four mid-class wheelsets, which were expected to have the
largest differences in comfort (16 spokes vs. 32 spokes, low vs. medium profile rims, etc) were selected.
On all 4 tested wheelsets the same Continental 4-season tires were mounted and inflated to a pressure of 7
bar.
3. Results
After a couple of initial tests the accelerometers were configured to measure acceleration at their
maximum range of ±6 g. Hitting a minor pothole results in an acceleration of more than 6 g, so the sensor
clips some times. In figure 2 top part, acceleration data in the time domain is shown. This data has been
corrected for tilt and filtered. The bottom part of figure 2 shows the speed during the 3 laps, where each
lap can be easily identified, due to the stop periods. The impact of different road types is also visible, for
example the difference between the smooth asphalt and the small cobbles is very high. Riding on smooth
asphalt happens just before 15:05. The transition from asphalt to the cobbles is not flat, but there is a
small bump in the road. The result of this small bump is clipping sensors at this point.
3.1. Tire pressure experiments
Table 2 shows the results of the experiments with the four different tire pressures. The data shows that
a lower tire pressure increases the comfort. Of course there is also a down side to lowering the tire
pressure: the chance of having a ‘snake bite’ flat increases and the rolling resistance increases too.