Rossett Ghyll is really pushing the limits as far as riding, and "whats acheivable" goes.(Its classed as a scramble in walking guide books!!)
Its a challenge for sure, but its only a decent I would do if I was doing a point to point route like the Coast to Coast.
To get the best out of it,I would advise a big travel bike,wide tyres,a dropable seat post,and plenty of body armour if your going to have a go.
To carry up would take an hour or so from the bottom of the steepest section.
The first part from Angle tarn is a stone pitched climb,possibly too steep to climb on the bike,Its a great trail from here on though (to sprinkling tarn) and one I plan to do soon.
From Allen Crags keep over to the right hand side from the summit Col shelter,If your on the right path it has a fast red coloured gravel trail down to the T junction for the Main Sca fell path,Awesome trail from this point, allthough its very rough and pitched,it potentially is one of the best/and longest/highest decents in the Lakes to Wasdale Head. 😉
Ime I would do the Bridleway from Styhead to Wasdale head farm that stays close to dingmell beck,its less busy with walkers and a nicer gradient,although its tricky to find from a cairn near Styhead coll,(Mountain Rescue strecher).
If you are a good technical rider you will love this route,if not,you will struggle,and I wouldent recommend Rossett ghyll to anyone as a good decent but,enjoy it if you do. 🙄