Most effective > 200 mile ride training On the 17th of August I'm doing a 250 mile ride in the UK in one day. I'm no stranger to longer rides often completing 100 mile rides and my longest ever was 175 miles (it was fairly unpleasant towards the end).

I'm quite squeezed for time, so getting really long rides in prior to this event is difficult.

My question is, what's the most effective training possible over several shorter sessions (perhaps up to about 2hrs long) between now and then? I can probably just about get 8hrs of training in per week.

I quite enjoy doing really hard threshold intervals, and I've heard sweetspot training is highly effective, but I'm just not sure if that's better than sticking in zone 2 for this event?

Note: I feel strong enough to complete 250 miles now, but I want to make it as pain free as it can be. I have a power meter so I can train effectively, and I also have a turbo trainer and the trainerroad app.
I did a ride of this length solo in March this year. I designed a route to suit me (not flat, not steep), and intended to be quick (I was aiming for under 21 hours). At 400km it was a tough day, but I never doubted I'd finish. I have seen people (tougher then me) go from a solid base of centuries/200km rides to this distance without anything in between, so it's possible. 

A few things that helped me get round (an hour faster than my target). 


all the riding I'd been doing. Prior to this I'd ridden at least one 200km (125mi) ride a month (often more) for over a year, of which several were 320+km (double centuries) in tougher conditions, though none for a few months before the 400km. When training for endurance, even commuting counts, especially if you've got stretches you can push hard. 
fasted training. Until I injured myself recently I was going out once a week for 90 minutes before breakfast. For endurance rides this is really beneficial - you don't bonk as easily or as hard, and you learn what it feels like to be out of carbs. Once a week is ideal, twice as an absolute maximum. This seemed to help after only a handful of training rides. 
a feeding schedule on the day. I set an alarm on my phone to remind me to eat, drink and stretch out of the saddle every half hour. I tried to remember to drink in between as well. This really helps when pushing a personal distance record. 
aim to cruise round. Hard efforts only on climbs and if you're riding in a group take turns at the front especially into a headwind. You don't have to be right on each other's wheels to get some benefit. 


A ride of this length is never going to be easy, and by going for it so suddenly you're doing it the hard way - so plan the actual ride carefully. Know where you can get a meal - you'll need real food - and where you can stock up on snacks and drinks. You might need to carry more water than you think. Know where the bike shops are in case you run out of tubes. Know how you can get home if things go more wrong than you can fix (it happens; it's happened to me twice this year). 

Apart from fasted training, I suggest you try to pack all your training time into long sessions, rather then hard efforts. You need the saddle time. But don't push yourself for a few days before the event.