City to City cycling

Billy-no-Money

You've obviously thought a lot about this!

I can't work out if you're a novice, or experienced but just not done this kind of trip (as you mention triathlons). So apologies if I suggest anything that you already know.

On bike reliability / repairs en-route, the main risk is of course a puncture which can be mitigated significantly by using tyres such as Schwalbe Marathon Plus. Other than that regular maintenance and inspection should prevent most other failures; brake cables don't just snap without warning for example. Carry a small toolkit which includes allen keys, any spanners you might need (most bikes don't have many nuts), a spoke key and a chain tool, along with a chain connector ('quick link' or similar names). If the chain breaks you can use the tool to split it and rejoin using the quick link.

Also there's never any harm in carrying some cable ties.

Make sure you know how to do running repairs; practice at home. Get a decent pump and try it out at home. Above all, do some similar distance runs within an urban area so you're near support if you need it, until you find your bike's weak points.

Also - consider doing the trip one way and using the train to come home if that's an option - but check your train operator's cycle restrictions. East Midland Trains and Cross Country both require reservations.

Route planning - Google Maps does offer cycle routes and it's not too bad, but I've found some instances where it's plotted routes where I certainly wouldn't choose to ride, including a road where cycling isn't permitted. But it's a good start; the worst thing you can do is simply follow road signs, because they will be set up for drivers and while you can legally ride a bike on most roads it very likely won't be pleasant. Even if a cycle facility is available you probably won't spot it until you've ridden past it. Unfortunately if you try to follow a signed cycle route you'll be frustrated; signs are hard to spot, and often disappear just when you need them.

I say give it a go; it'll give you a good sense of purpose.