When to Change Gear Cables?

[Will Spin]

Carry a decent size safety pin to poke the broken end out. Otherwise it's a devil to get out. The safety pin may come in useful for other (eg repair) purposes.

Unless you are crossing the Sahara or somewhere equally remote, it isn't worth contemplating changing gear cables whilst out on the road if you have brifters. It really is a job best done in a workshop with the right tools and materials. You are better off carrying a cable tie or two so you can tie up the derailleur so that you are in a gear that will get you home.

 

[Blue Hills]

Being a happy ignorant flat bar rider, this had never occurred to me. Another argument in favour of flat bar touring. Simple job with modern rapidfires.

 

[Ajax Bay]

thinking of going for the higher-end Jaqwire stuff - any advances on that from anyone?

I used a Jagwire set and they did me very well (I left it on longer than I should've). They have some shiny gold bits (ferrules) too.

Unless you are crossing the Sahara or somewhere equally remote, it isn't worth contemplating changing gear cables whilst out on the road if you have brifters. It really is a job best done in a workshop with the right tools and materials. You are better off carrying a cable tie or two so you can tie up the derailleur so that you are in a gear that will get you home.

Will - have you tried to do that with a cable tie, or two?
With all due respect, Will, that 'stagger home approach' presupposes that the rider can't index their gears in the first place. If a cable breaks (and you have a spare or can get to a bike shop for a spare) then by all means temporarily set the front derailleur on the smaller (or middle) chainring, or set the RD on a central sprocket. But as soon as convenient, stop, remove the broken cable, replace with new, undo the adjusted limit screws and reset/index the gears.
"[It is a job best done in a workshop with the right tools and materials." Please say what tools and materials you'd need to replace a cable that you'd have in your workshop but you don't carry on a ride. For me it's a safety pin, a spare cable and a hex key.
Last time for me was 60km into a 600 (Wales end-to-end, and back). FD cable broke at the crest of a hill (so the chain defaults to the small ring); spun like a crazy fixed rider down the hill (when not aero); stopped at the roadside; set the FD on the middle chainring; removed the cable; rode to Rhayader (where I knew there was a bike shop); bought a new cable and a coffee; fitted it and adjusted it; and rode on (less than 15 minutes). @Ian H advises against carrying a spare cable. I paraphrase: "If you think you need to carry a spare cable; install that 'spare' before that ride."
"Can't" means "haven't yet done". Learn and practise indexing gears (front and rear) - don't wait for the Sahara to come to you.