A few short notes about the route. Norway.
Rallarvegen, from Haugestøl to Flåm.Navigating the Rallarvegen is pretty easy, either starting from Mjølfjell or Haugestøl. If you choose to start in Haugestøl it reduces the amount of climbing you have to do. From Haugestøl you follow the path until you reach Myrdal, where the signs tell you to turn left to get to Flåm or carry straight on up to Myrdal and the short train journey to Upsete. The bulk of the route is on grit tracks until you hit the asphalt road after the turning Flåm, just down from Myrdal train station.
The quality of the tracks is very variable. Up to Finse the road surface is generally good and gradients not particularly steep. It is thus not surprising that you are most likely to encounter large groups of day cyclists and families with small children cycling this section. It is possible to hire bikes and take an organised tour from Haugestøl and many people choose to do this.
After Finse the track and terrain become more demanding. There are short steep inclines and longer uphill sections. Some sections of the track are extremely rough which seems to be a result of repairs made after the track has been washed away. In 2007 we encountered some rough sections in the last five kilometres to Myrdal. On our 28" wheel bikes we walked these short sections as it wasn't worth risking a fall or broken wheel.
There are around twenty harpin bends after the junction at Myrdal. Whilst it is possible to cycle down and up this section you have to be very careful and/or know what you are doing. The road surface is very poor in places, and the gradient quite steep. Other sources on the internet talk about you melting brake blocks on the way down. I think this is a little exaggerated as you would not want to go any faster than walking pace on the way down. However it is probably the most dangerous and technically demanding part of the Rallarvegen.
A feature which varies from year to year is the amount of snow to be found. In 2006 the track was completely clear whilst in 2007 there were a number of snowfields some over a hundred metres across. We had to walk across all of these. A related issue is that no matter how sunny it is in Haugestøl the weather can close in very quickly and there are precious few places you can shelter should you get caught in a storm. So take full rain gear, extra clothing and sufficient food when you venture onto the Rallarvegen.
There is a cafe (and museum) on the route close to the highest point. It shuts before five even in the summer season. In 2006 the coffee and waffles were good, and the cafe was very warm.
Sognefjorden including Jøstedal and Fjærlandsfjorden.
There is not much usable land on the sides of the fjords and not surprisingly all of it is in use. This means that outside of the larger towns you have to cycle on the main roads. Fortunately our experience of the 55 is that traffic is light. The only issue we experienced was with tradesmen's vans (green number plates). Everyone else gave sufficient room when overtaking. In a few places old tunnels and road sections have been turned into cycle and pedestrian tracks.
Between Sogndalsfjorden and Gaupne there is a fair bit of climbing. The first part starts a few kilometres out of town and ends by Hafslovatnet. After skirting the lake the second shorter part of the climbs starts ending at a viewing point looking back down to Hafslo. The descent on the other side (or climb if you are going the other way) into Marifjøra is a fast and continuous downhill. It is great to go downhill and a slog going back up it.
Jøstedal is a reasonably gentle valley rising to around 250-300m. Every now and again the road climbs sharply away from the river before returning to the same level as the river. We did not find we had problems with traffic except for the occasional car (usually non-Norwegian) that did not give us enough room.
As far as we know it is not possible to cycle to Fjærlandsfjorden as the tunnels into Fjærland are closed to cyclists. We don't know if you can take a bus through the tunnels with your bike. We took the ferry from Balestrand up to the Fjærland Kai and then cycled the short distance to Bøyum camping. This campsite does exist although it was not on any of the maps and guides we found bar one.