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170 grams for a bit of insurance.
I'm the worrying sort so that'd be a no brainer - if it's pissing down I want to change the tube and get moving again ASAP. Also, I guess not so relevant since you're self-supported anyway but there can be very long stretches with no cellphone coverage. This is a big mostly empty country. Edit: tyre != tube, duh :|
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Spare tyre or no spare tyre?
I've only ever had tyre failure twice, once on TCR and then again on Ipwr. Both were sidewall punctures, one tubeless, one with tubes. Both times I was able to patch the tyre up and ride 1000+km on it. So I still wouldn't take a spare. Just make sure you have plenty of patches and something to make a boot with.
Spare tyre or no spare tyre?
170 grams for a bit of insurance.
I didn't take one on TCR but the population density is much higher so there was unlikely to be 100i hike to the next town.