Hmm sweeping generalisation alert.
OS (and equivalent maps in other countries) also include the small back lanes and bridleways that simply don't appear on larger-scale maps. So they have definite advantages as well as disadvantages. 1:25k is too much but 1:50k can be worth considering, depending on what sort of cycle tour you are doing: for example try doing the South Downs Way or the Ridgeway with a road map - or to take a less extreme example, I'm not sure how many of the Sustrans routes you could follow with a road map.
For cyclists the ideal map would probably be 1:100k linear and custom-printed on ultralight waterproof paper.
Oh, and don't forget the Sustrans and Harveys linear maps which can be useful.
Another sweeping generalisation
The best cycle map series I have ever used are the German 'Bikeline' by Esterbauer maps.
They are all at 1:70,00 (I think) which they have found to be the perfect size for cycling, their are printed in landscape format which means the maps fit in almost any typical bar bag the right way up.
Most importantly on a map designed for cars, the motorways are in the main colours and the footpath and cycle lanes are barely marked. On their cycle map the colours are reversed, so that motorways are greyed out, so you don't even think to use them. Hills are also marked as are the alternate routes around them.
I'd love to see a Bikeline map of a classic UK cycle route such as the C2C it would blow other maps such as the Sustrans version (which won an award. Why ??) out of the water.
