No place for a tri bike (IMO) and a compact or triple ring at least IMO
Why? Most of the route is undulating/flat – there are only really two climbs where you get out of the saddle – one up away from Ullswater early on and the other being the struggle. The descents aren’t technical enough not to use a TT bike. You can pretty much spend the rest of the route on the tri bars. I wouldn’t use deep section aero wheels, but light weight wheels with a TT position are perfect IMO.
And double & 12-28 for me 🙂
Anyway, swim is lush, every breath has a slightly different, very beautiful view (it was last year in the sun anyway!). Bike is nice, Struggle is great – crowds line the road TdF style. The ‘run’ is brutal if you don’t have many walking/hiking miles in the legs. Learn to ‘run’ downhill on uneven ground – get plenty of practice at that. There’s a great scramble up near the top.
It’s very rewarding!