Have done something similar. IIRC I went Skiddaw – Lower Man via old railway line & old coach road to then traverse up the Dodds. Up to Helvellyn proper then down Dollywaggon to Grisedale tarn, up a bit then down the tongue to the main road. Had a bit of a break and shied away from more climbs so cruised round the back roads to Langdale. Left the bike at the bottom of Rosset Gill, and nipped up to do the rest in fell shoes.
If you want to make it a complete loop then I’d carry up Rosset Gill leave your bike at the watershed and jog the rest of the tops. [edit – return and pick the bike up again, and then…] Make the most of Styhead Gill – Seathwaite, pick up the first part of Seatoller, then Borrowdale Bash/ Catbells. That and the above is mostly offroad and rideable up/down as far as most other options. You could add more off road doing a less direct route (eg descend W off Helvellyn to Townhead – Easedale- Stonethwaite – up Langstrath…) but that’s pretty contrived IMO.
One for the summer obviously as it’s quite a long day out.
Twinkyldave’s post looks interesting though.