Our Skoda Roomster - the day before it goes to its new owner!
A few comments.
The very low pressure under the front undertray would be over only a small area - the puck was placed at the point where the undertray has a short projecting downwards curve. The low pressures under the rest of the car reflect that it's not that untidy underneath - the front undertray, some side undertrays and a spare wheel well that's at a similar height.
The -220 Pascals on the roof is a mystery to me. I rechecked the data and that's definitely the average of what was logged. Looking at the logged pressures, this tap varied a lot more in pressures than the others on the roof. If we were keeping the car, it might be interesting to tape up the roof rails. I've also not tuft tested this car - perhaps tufts might show something. Maybe A-pillar vortices interacting with yaw airflow across the roof rails - but that's just a complete guess.
The increase in pressure at the back of the roof (ie it is not as low) is probably caused by the flattening of the roof - it's not quite a spoiler but the roof stops dropping away.
The two pressures measured in the wake are basically the same.
