This section is a diversion from the main route, beautiful beaches and wonderful views.
I took a group of Americans here a few years ago. They were experienced cyclists who had ridden widely in the USA, Canada and Europe. At the end they said it had been the best bike ride ever. Fortunately the weather had been kind as there are often long spells of settled weather in the early summer.
The area falls into two parts as far as cycling is concerned: Coigach to the south is not dreadfully hilly. Cycling this is inevitably out and back. A rough track is shown on some maps leading from the road end east of Achiltibuie to the A835 near Strath Kanaird. This is difficult scrambling and taking a bike is out of the question.
All the same you should go to Altandhu, Achiltiebuie etc. There are some lovely beaches combined with distant views of the mountains to the north. There are also interesting places to visit.
Further north in Assynt it's sort of hilly. A B&B owner in Lochinver once told me that she was expecting a family from Surrey one evening. They planned to cycle from Kylesku via Drumbeg. They knew it was hilly but it was only 25 miles after all. She got a phone call at 3pm in the afternoon, they weren't even half way round - she drove round and collected them.
Cycling to Achiltibuie you should go the longer way via Altandhu. There is a wonderful panorama of the Summer Isles a mile before Altandhu making the extra distance well worth while. There's a pub the Fuaran Bar at Altandhu, also a fish smokehouse where you can see fish being smoked and of course buy the product. Just south of Atlandhu is Old Dornie harbour, opposite Isle Ristol, a pleasant place to stop. Further on you'll pass a craft and coffee shop at Polbain. Continuing south again you run into Achiltiebuie. Achiltiebuie has the Hydroponicum, a warm damp place to sit if it's cold and damp outside. This is a complex of greenhouses with plants grown without soil. You can have a guided tour or simply sit and drink coffee surrounded by all the flowers.
For other parts of this route, click Related above.