This is certainly the most hilly road in Scotland
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.
This is possibly the most scenic road in Scotland, it is certainly the most hilly. In days gone by you could camp wild on the coast here but erosion problems have meant that campers are concentrated at two sites, Achmelvich and Clachtoll. The start of the road is signed: 'Kylesku Tourist Route'. There are a number of minor roads leading towards the Point of Stoer which are worth exploring. Just before Stoer you come to a memorial to the Rev Norman MacLeod who eventually settled in New Zealand with his followers. On the way they also tried Nova Scotia and Australia - all by sailing ship too. After Stoer you pass the golden sand of Clashnessie Bay, then climb up to Drumbeg where there is a hotel. After this there is another plunge to Loch Nedd - watch out for sharp bends. There is a sign 25% descent. Is it possible to have a road with 25% descent? Certainly it seems like it. Towards the end you get the occasional dramatic view of the mountain Quinag. The road joins the A894 just south of Kylesku. There is a hotel at Kylesku doing bar food. You can also take a boat to the Eas Coul Aulin Falls, the tallest waterfall in Britain, a 200 metre drop. This is not a big waterfall in volume but the surrounding scenery is undeniably impressive.
For the other parts of this route, click Related above.