That's going to be an absolutely brutal ride as 100 miles off road is a a big challenge on its own but that's a crazy amount of climbing. I did a ten hour endurance race with that rate of climbing and it was savage as you were either climbing or descending, there were hardly any sections that were reasonably flat. Admittedly I was doing that on a rigid fat bike which was badly suited to that type of riding but even then, your event sounds like it's going to be extremely tough. Your fitness is clearly very good though and if you keep up the riding over the next month I think it will be doable but it will be a case of how tough it's going to be.
I stopped doing MTB endurance a couple of years ago although had thought about reviving my full suspension 29er as I find descending gets tiring on a rigid or hardtail whereas on the FS bike you can just unlock the suspension and let it do the work. On the other hand though I find MTB endurance riding not that fun as you have to worry about conserving your power, that's fine on a road bike but I find it frustrating not being able to stamp on the pedals and accelerate hard through technical features.
I did a different 100km race last year as it was 70km on road then through a transition point to swap to the mountain bike for two 15km off road laps to make up the 100km. I have one of the plushest road bikes going with its big 32mm tyres, carbon frame and both front and rear dampeners but getting onto the hardtail plus 29+ mountain bike felt like sitting on a very soft armchair. Although I was almost caught out by the braking because although the road bike has hydraulic brakes the lever action is not as responsive to stop people crashing but on the MTB they are very responsive, I almost crashed the MTB as the brakes just felt so wrong in comparison.
I said I'd never do it but I'm now giving serious thought to doing a Lands End to John O'Groat attempt, I've been told I have to take a shift off at work (we've been through a very busy period and had to do crazy amounts of unpaid overtime) which would mean I'd have three weeks off and I'm feeling I should try to do something with that. When I've done 120+ mile rides before they've absolutely killed me and I've not wanted to see the bike for at least a week but then I am terrible with pacing, I'm always trying to do it as quickly as possible with minimal breaks which makes it much tougher at least for my fitness level.
When I did the Loch Ness race a couple of months ago I found it very easy going compared to last year as I'd done it at a slower pace with a friend but looking at the stats it wasn't that much slower, last year I averaged just over 17mph finishing in three hours an 54 minutes. This year my time was four hours 36 minutes with an overall average speed of 14mph and a moving average of 15mph so I'm thinking 100 mile days are definitely feasible if I can pace myself properly. Plus if it all goes wrong I can just abandon it and get the train home. If I did it over the summer I'd have long days so there would be no rush to get in for a certain time and if I could keep a flexible schedule then I could take a day off if the weather was crap or I was needing a break.
Baggage was another concern as I didn't want to have the bike loaded up with heavy gear, I've been looking at panniers but I couldn't really see any that are particularly lightweight. I was having a look at racks in the bike shop today and came across a saddle bag that straps onto the seatpost and seat rails which looks great, it would give me 12L capacity and some protection for my rear from the back wheel in the wet. In addition it would work for all my bikes as it just straps onto the seat so if I did ever fancy doing something longer on the mountain bikes, it could be useful for that too.
I have a fantastic little 4L backpack which was a little pricey but it's so well made it's still in perfect working condition after many years of abuse so I've invested in a larger 12L model as I wanted a backpack that could take the drone and additional clothing but not be too big either. However I'm also thinking it would be great for a Land's End to John O'Groats ride as between that and the saddle bag I'd have a fairly decent 24 litre capacity. My plan would be to stay in Travelodges or similar which I know would be pricey but I'd want a good night's sleep and I'd have a chance to rinse out clothing so I wouldn't need to take a huge amount.
What are your thoughts on how to do such a run, have you given it much thought? I realise the simple suggestion would be to load up the bike and start doing some test runs both to see how that works and check my fitness for multi day long runs but then I think that will just put me off the idea whereas if I book it all and dump myself in the deep end, I have to see it through otherwise my train fare down and back would be a waste.
The weather is still surprisingly awful here but I was determined to get out so grabbed the rigid bike and did a three hour ride on Thursday night when it was four degrees celsius and constant heavy rain. On one hand it can be quite satisfying to be able to take on such conditions and have fun but at the same time it's getting ridiculous it's halfway through June and I'm still using my winter setup. I popped out for a quick 20 mile ride this evening and glad I didn't go out for more as I was feeling the spots of rain as I reached the point I was heading home.
Leviathan - AMD Ryzen 9 3900x, 64GB DDR4 3200Mhz ram, Nvidia GTX 1070 8GB, 2TB SSD/44TB HDD, BD-ROM, Dell U2711/HTC Vive