Well, I did it!
Here's a write-up I did for my club website.
...I managed to get myself a late entry to the Upper Thames audax - my first one since PBP. It goes in a big loop which starts near Didcot, loops down to the Chilterns (going up the ridge at Berins Hill), skirts Henley and heads back up to Christmas Common. Then it goes across to the Cotswolds with a stop in Chipping Norton before looping back towards Didcot. Here's the route: http://ridewithgps.com/trips/438336
With half an eye on the 24 hour time trial next year, I decided I would crack on on on this ride, aiming to finish in daylight, which would mean getting back by 4:30 (7:30 start so 9 hours). Also I wanted to see how I got on with eating while on the move so I decided I would only stop for the two controls and only for the bare minimum of time. One advantage was that I did the ride last year (first time I've repeated one) so I knew the route. While it's not terribly hilly, there are some exposed sections and it is a good bit over-distance at 214km.
It was also the first time I'd used a heart rate monitor on an audax and it was interesting. I was surprised how much higher my heart rate got compared to on time trials, sometimes for long periods (I'm actually a bit worried that it means I've not been trying hard enough in TTs!).
During the first part of the ride I mostly rode 3-up then 2-up at a fast pace. The heart rate monitor was very handy for this as I could use it to guide when I could up the pace and when to drop off. A fair bit of this stage was done into the headwind so it was good to share the burden.
I finished the stage about 10 minutes under 3 hours. This was by far the hilliest section so I was well on track but I knew I would slow down as the day wore on. I also lost my partners (one to a puncture, the other to an early lunch) and, being near the front of the field (of 70-odd riders), there were no others near me.
The next stage was therefore quite hard with a bit more headwind and the long pull up from Bicester to Chipping Norton. I had to make a couple of stops - one to buy water and another because, amazingly, a friend riding in the opposite direction recognised me, shouted out, and we had a quick chat. Eating on the go was going well. Sausage rolls, bananas and muffins were all going down smoothly, with only one minor reverse - I'll spare the details.
This ride coincides with peak hedge trimming season and, as last year, there were loads of punctures. I was pleased to pass the spot just before Chipping Norton where I'd got mine last year. I was also pleased to get into Chipping Norton at 1:35 - only 5 minutes down on my schedule despite the stops. Leaving at about 1:45 after buying more drinks, I had 2hrs 45 minutes to do the last 73km. I felt quite confident as, although it was slightly longer than the other legs, and I had been going all day, there was going to be a tailwind and some long flat sections.
It worked out to plan. I had to keep pushing and my heart rate was still hitting high levels on every climb, but I got in at 4:28 - two minutes ahead of my objective on a 9-hour ride! Two others passed me in the last few miles, having the same objective, and I was fourth rider to finish.
A good day out. I enjoyed doing an audax after a few months off, achieved my objective, and feel happy about eating on the go, but it was nowhere near the sort of speed I need to maintain to get a decent 24hr distance. Weather and hilliness permitting, I'll try and have a shot at one on my time trial bike soon and see how that feels for speed and comfort.