You are describing some of the routing on the Wessex SR audax rides! If it doesn't have grass up the middle, you've taken a wrong turn.
Sounds ideal ..
Yesterday I tried the same route again, got it done.
How it went -
Started 7.30am aiming to finish late / early am. Rode to start of Ridgeway double ITT route and started that at 8am. Used the drop-bar 650B bike as it has dyno lights - but riding a road-biased 'all-roader' on a mostly off-road route was harder than I thought on the return leg. The Ridgeway is generally pretty smooth and this bike had Horizon 47C tyres, but there's enough lumpy hardpack and narrow ruts to demand a lot of out of saddle riding and that got to me. The bike just isn't as comfy as an MTB when ridden like that. A lot of "arrrgh my neck/shoulders" stretch stops. Other stops to stretch-out in a way that I often need to on long rides, more so this ride though. Niggly, flow-breaker kind of stops.
It was hot, 28+. Those white roads reflect a lot of heat. I really felt it early-mid afternoon but the steady pace I aimed at meant I wasn't sweating too hard.
Flints. Fking flints, everywhere..! I know this so why didn't I top up my sealant the night before? Partly because I just jumped at the weather forecast on Friday to ride this on Saturday, and partly carelessness. 5hrs in, flat tyre, no sealant coming out of the small nick. Topped up with most of the content of the small bottle I had with me, now worried about the rear for the rest of the ride. Rear also seemed a bit squidgy - pumped it up. This became a recurring theme of the ride ..
Eating. Ate and drank plenty over the first outward leg. Was planning on a good food stop halfway, brought a pour-store bag of rice with honey and planned to stop at the shop on the way back ~3/4 of the way through. Not sure why but the sweetness was too much, maybe the heat also. Felt that stomach churn that I got doing a 300km a few years ago that meant I rode 180km or so pretty slowly, on empty. Not good .. churn got worse and had me feeling pretty grim, slowed right down. Had a very slow 3rd quarter of the ride between Fox Hill and Goring. Felt good enough on the hills after that toblow my knee again, it'd been fine for 150 or more miles than the warning twinge and the 28T front up every hillafter that. Not a bad lesson in pacing though - taking the hills like this generally is probably the way to go on a big day ride.
All in all though, what a day to be on the Ridgeway. It's really beautiful and passes through some quite empty landscapes. There are sections that may be some of my favourite tracks in the area, the UK's strada bianca. Rolling hills and dirt tracks that made me think of other places I've been on trips away. More so on the way back as I rode through the golden hour and the white roads turned yellow, then the orange-red light among the trees at sunset. Lovely. Would have been even nicer as part of a 3hr ride rather than 17 though! Finished feeling OK, beat-up but not bonky or overly done-in, so eating issues aside that's a success.
Lessons -
Choose my food better. This ride confirmed it, I should stick to mostly savoury, real food. I stopped at the shop for a chicken tortilla wrap and milkshake and it was amazing .. Picked me up in no time. I was craving a bacon and egg sandwich .. Meant I stopped at the shop for longer than I needed, savouring the food : ) Cue a 1am cook-up after I got home!
Top up your sealant, dumbass.. That little error cost me prob 45mins in total - the flat fix then maybe 8 stops to top up both tyres' pressure. But I did get a really interesting experiment in tyre pressure done .. that sinking feeling .. Horizons on 25mm rims feel fine right down to maybe 20psi. The ideal pressure is probably lower than the 27ish that I've been using.
Drop bar bikes .. I love them but if I expect a lot of off-road ie >5 hours at a stretch .. No. Or, I need to work on strength to cope with it. Feel a bit beat up today. Triceps and arm tension that was felt in my neck. This bike is armchair-comfy on road centuries but here it beat me up.
Edelux II light - brilliant on road, not so great on woodland trails. Compared to usual night-riding in the area with my L+M, really slow going in places on the way back because of this.
Lastly - don't use ITT routes for things like this? I ignored my GPS for the first leg, only checking the time at the end of 1st leg (7 1/2hrs, just under 4 from Ivinghoe to Goring - about as expected). I didn't want to 'TT it', just to ride and pace consistently. But on the way back I was thinking '15hrs .. 15hrs .. ', the leader board on the site in mind. Took longer than that in the end, gut ache and flats accounted for a chiunk of time, yet I'm not posting a file to be checked as an ITT attempt anyway. Just that ego gets to me - pretty normal I think? In the end it made no odds to the ride apart from being on my mind during a ride where I wanted to get away from that and focus on managing my pace. Might try another 300km on a different route for this reason.
Anyway .. all just experience. I've never set out to do day rides like this before. All my longer rides in the past have been sub 12hrs or training focussed on higher intensity over maybe 12hrs then a bivi and another 8-12hrs. Have to say, 13hrs for the RW double ITT is impressive. 13.5hrs on a SS perhaps more so, it's really not a quick route for a SS imo. Wasn't when I SS'd my variant of the out-back anyway : )