I put together a page on this for my mother’s website:
Cycle routes
Now that we’ve got kids, I’m usually pushed for time and will either just hit Whinlatter or drive to either Keswick or Honister for an early morning Borrowdale Bash.
If you fancy a big day of carrying your bike, you can ride to the far end of Buttermere and do the four passes loop which is a great day out as long as you have the right expectations.
Another favourite is the Lonscale Fell loop (Keswick to Threlkeld, then follow the BW past the Blencathra Centre towards Skiddaw House, then back behind Latrigg to Keswick), although I’ve not done it since the bridges fell down on the railway path and I don’t know what the alternative via Brundholme is like.
Don’t bother with the tempting looking BW from Loweswater west of Mellbreak: it’s a bog, and the BW to the side of Buttermere is very dull and always busy.