Lower gears for climbing, Shimano 105

Get yourself a Wolftooth and use a medium cage 105. Got a 36T SRAM WiFli sprocket fitted to the rear of my Shimano set up, running well.

It'll mean major surgery: a 34 inner ring, a 34 cassette and a long-cage derailleur - or a wolf tooth hanger to lengthen it. You should be able to get up most things on that...

That's a 0.70 ratio, WOW, that must be cool.? I love my Cinelli at 0.75. Huckfinn hope you get it below....

The old 105 derailleur probably won't go too far past its published capacity but if you get yourself a Wolftooth Roadlink or something similar you should be able to fit a far bigger cassette.

Alternatively switch out for a new 105/grx/ultegra Rx deraillieur and you should be able to get 11-40 working easily without too much bother.

There was an article on here saying you could run 11-40 on 11-speed 105. Personally, I've got a 50-34 compact and 11-34 11-speed 105, which generally does me fine (and I'm rubbish at climbing )

My Jamis touring bike came with 105, circa 2013.

24/32/42 front triple.

12-30 10-spd cassette, changed to 11-34 when it wore out, no shifting issues. 24-34 is good for vertical walls or pulling tree stumps.