We ride a lot around the Coniston area. I’ve plotted a route on OS Maps here which is based on one found in a popular routes book:
MTB Routes – Around Coniston (osmaps.com)
Starts and finishes from the Sun Inn, only downside is a very stiff climb at the very beginning of the ride up to the car park at the beginning of the Walna Scar Road so make sure you warm up first!
Turning back northwards, the climb around High Nibthwaite is a difficult one but the view of the south end of the lake from the top is spectacular.
There’s also the option to extend the ride around Tarn Hows and pick up the Bridleway at Glen Mary Bridge which really would make it quite a big day!