I think for a non-competitive event like the one mentioned it might make more sense to compare cycling to walking. For me a brisk walk is about 4 mph, the same level of effort on a bicycle is probably about 12 mph.
The SSS is a difficulty score based on how easy or difficult it was to run a quick time in a given race. The harder it was to run a quick time, the higher the SSS score. The way it is worked out is by looking at people's times in a particular race and comparing it against their previous performances. As a very simplified example, if 100 people run in race A one weekend, and the same 100 run in race B over the same distance the next weekend, if, on average, the field is 60 seconds slower in race B than race A, there was clearly some factor (be it weather conditions, accuracy of course measurement, type of terrain, competitiveness of the field, how hilly the course was etc) which caused times to be slower. Therefore the SSS for race B will be higher than the SSS for race A.
Sometimes the system doesn’t have enough data to run the calculations properly – for example if there were only a small number taking part and only a few of them have profiles so we have limited access to previous performance data. In this situation the system gives a notional value of 1.0.