Did some practice packing tonight with 50% of the gear I'll be taking. Obviosly I'll be wearing the other 50% of it so I've stuffed the bag with some sweaters to add weight for my practice with the bag tomorrow. I usually cycle with a normal back pack so I've no idea if this will be better or worse.
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Today I took a fully loaded (20kg) pack over 38km of local mountain road to get a feel for what I'm up against. I can honestly say I think I'm ready but I've got serious worries about my colleague who'll come with who hasn't done any prep training on the bike.
The first 19km were comfortable with the pack on and the bike rode well over the rougher road surfaces. I wore my track bottoms with the long-Johns under which caused me a slight over-heating problem and made me slightly uncomfortable in the legs while me feet were pretty much ice blocks with just the footie socks and my bike shoes. I wore a woolly hat which was toasty but again, it felt like it was over-heating me. My neck scarf/ buff thing was totally unnecessary.
For the return leg I packed the bottoms and went with the Lycra leggings over long-Johns which were perfect for the weather (~2/3 degrees + 8kph wind, dry). I put some cheap plastic shoe covers over my socks to go inside the shoes which also worked a treat. I bagged the neck buff and woolly hat in favour of a skull cap and helmet combo which was not bad, if a little less comfortable. Coming home I deliberately hit every pot hole, sunken manhole cover, broken bit of asphalt and uneven surface I could find to put the tyres and tube through the works and they just took it in their stride. Had a few close calls through the traffic but the brakes are in fine order bringing me from 40+ to less than 10kph in under a second.
The pack started to get my upper spine aching towards the last 5km which I managed to help by tightening the hip straps and allowing my abdomen to take some of the weight. I'm sure it was just a matter of the straps being wrongly adjusted as the first leg gave me no issues with the pack at all. Either it was the straps or I'd packed it wrong; it was only carrying a few more kg than on the first part of the trip.
So in conclusion: The gear is fine. The bike is (I think) tough enough and the pack is fine as long as it's worn correctly. I think my body is in good enough shape so all I need to worry about now is booking hotels ahead of time to make sure I don't end up sleeping in a barn when I could really do with a soft bed and some sort of heating system & shower.