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I cycle in sandals throughout the summer. If it's warm then my feet get a patchy sun tan, if it's cool I use socks and if it's cold and wet I use waterproof socks. They eventually get wet through but still provide some warmth and are much easier to dry than soggy boots or cycling shoes.
I prefer SPD cleats over sandals on platform pedals. That said, my last tour was planned to be in warmer weather, so I wore sandals in rain when it would be too hot for rain pants. And it was warm enough that I wore sandals in the campsite too. I used Shimano A530 pedals that had a large enough platform on one side that the sandals with a fairly stiff sole were comfortable and SPD cleats on the other side.
But I am already struggling to minimize too much weight, do not want to carry sandals, and bike shoes, and hiking shoes. That along with some flip flops for shower shoes.
Photo attached from that tour, but the photo was taken after the rain had quit. Yes, I am wearing socks with my sandals.
My bike shoes will be Keen Commuter 4 cycling shoes (discontinued). They were sold as a sandal, but with a closed toe I consider them to be shoes.
https://www.biketiresdirect.com/reviews/keen-mens-commuter-4-cycling-sandalhttps://www.treefortbikes.com/Keen-Mens-Commuter-4-SandalThey are slow to dry out but I have some cycling overshoe covers that I plan to wear with them when I wear rain pants that can overlap over the overshoes. When too warm for rain pants, I will wear waterproof hiking shoes with waterproof gaiters.
Thanks.