I went mountain biking yesterday, when the temperature was 100F / 38C. This is in Southern California in June, so that's not that unusual. The only issue I had is that my shoes get uncomfortably hot, especially the toes.
The trail I rode is just a climb to the top, then a descent back down to the start. There's no shade, and until the descent, there are no opportunities to get airflow that would help cool things off.
My shoes are SIDI Dominator. Black, of course.
I have a similar problem with my road shoes, which are the SIDI Genius 5. It's not as bad, because I'm usually moving much faster on the road, but it's still bothersome.
Buying new shoes is not an option right now, so I am looking for ideas to alter the shoes to be cooler. I want to avoid cutting holes in the shoes, so I came up with two options:
Paint the shoes white or silver. Black absorbs heat, white should reflect it.
Tape some foil on the shoes, especially the toe box. This will look goofy, and durability is questionable, but it should offer the highest level of reflection.
Duct tape. I'm thinking of the classic grey duct tape. Simple, durable, and probably a decent reflective quality.
Anyone have any better ideas?