Despite several trips to Spain, I’ve never fully understood the road numbering system. Some of the fantastic roads, that seem to be everywhere in Spain, might start with an N, others AS and then there are those starting CL, CA and numerous other prefixes.
While it appears to be almost impossible to plan a disappointing route through Spain as long as you avoid the motorways, here is a (very) rough guide to the road numbering.
Autopistas (AP): Likely to cost you money, so unless you need to cover a lot of miles, in a time-efficient yet soul-destroying way, these are to be avoided. Also, the cost may vary depending on the season.
Autovias (A): Are (mainly) free motorways. Still to be avoided. There is a saying in Spain there are busy motorways and very busy motorways.
Then there are pseudo-motorways built by the regional governments. In Catalonia, the C25 which links Girona and Lleida, is a motorway, but not always shown as such on maps.
There is a whole science to how Catalonia numbers their roads. It is based on the direction the road travels, which then defines the first number for that road. However, life is to short to try and wrap my head around it.
National (N) roads are a close equivalent to the UK arterial (A) roads but without the traffic. The N-260, arguably one of the best roads in Spain for a motorcycle, is only just wide enough for two cars to pass in some places, but definitely worth riding.
Roads starting CA/L or B typically means tighter twister roads, probably mountains or forests. They turn the grin factor up to 11, but nowhere you want to make a mistake.
Then there are the roads where the letters indicate the region you are in, and around Madrid it just gets crazy. There are “A” motorways, “M” motorways (for Madrid) and “R” motorways (for Radial). All totally bonkers unless you live there and then I’m sure it all makes sense.
All of that said, if you avoid the AP and A roads and avoid significant towns and cities, Spain is going to offer you some of the most motorcycle-orientated roads in Europe. It is hard not to have a great time.