This morning I could not find my training shoes. So, I used my sandals. I found that the sandals not only kept my feet cool but there was no pedal slippage as I had expected. The more I think about it, having no laces is probably another advantage. So, which footwear is best for summer cycling?
When summer comes around, I love riding around in my Chaco sandals. When using any non-cycling shoe on a bike, you'll want to have proper pedals with a good grippy platform, I particularly like the MKS Grip King. The biggest danger is probably getting the tops of your feet sunburned.
I wouldn't recommend flip-flops or non-sport sandals, but sport sandals are perfectly fine on a bike. If you want to get seriously dorky, you can even get SPD-cleat ready sandals from Shimano or Keen.
I commute by bicycle in the summer in Sacramento, CA... there are days when it is so hot in the afternoon that I avoid brushing against the steel frame of my bike because it burns the skin to touch!
I agree that open-toed sandals are not such a great idea for cycling--even when overheating is an issue--but I also believe that heat stress is a real problem that must be dealt with. Cooling my feet off isn't my highest priority, but it is certainly in the mix.
The solution that I have found are close-toed sandals. In fact, I have found a pair of closed-toed sandals that accept cleats for clipless pedals. I roll with SPD's in my sandals in the summer. I'm riding in Keen Commuter sandals in the summer: http://bit.ly/hyo1M5
My one issue with them is that I need to cinch them very tight in order to not feel them moving on my foot when I'm lifting up on the pedal. Otherwise, no complaints!
Sandals are fine for casual pedaling, but are unsafe and innapropriate for more energetic efforts. Good rule of thumb? If you're going for coffee, and not on a hard core road bike (or in a group of friends that make everything a race) then sandals are probably ok. Less than 5 miles an hour, probably ok.
Road bike? Racer buddies? Off road, even a little bit? Wear the trainers. And BTW good, ventilated, light weight trainers are just as comfy as sandals, but are a lot safer. Sandals at low speed may have good traction on a pedal, but sandals at higher speeds are unlikely to maintain good traction between both the pedals and the sandals, and between the sandals and your feet.
Even better, consider a pair of cycling shoes, with pedals made to fit. They'll have the best traction, and really high quality shoes are very comfortable and well ventilated.
Generally sandals aren't good riding shoes.
I happen to think sandals are a bad idea. They provide next to no toe protection.
I know people who have ridden in the winter with sandals and love them. (Goretex socks as outers for water protection and whatever you need inside for the temperature).
But the problem is there is so much crap on the road, you never know when something will pop up hit your feet.
This was funny as after reading about the guy with the Goretex socks, I tried my ride to work in sandals, and actually hit a bit of wrapping (The stuff the tie up stacks of wood or things on pallets with) that was on the ground, and whacked my toes pretty badly.
The more I looked around as I rode on the street I realized there is way too much crap on the road for sandals to be a good idea.
As zenbike said, to hop out for coffee, sure. But if you are going to do any road riding, it seems ill advised to me.
There are Shimano SD65 sandals with the SPD cleat, cleats being a safety feature IMHO as they keep your feet on the pedals even if you are not fully clipped in, with less scope for your feet to slip off the front of the pedals. Couple these with Time rather than SPD cleats and you get ankle movement and do not have to constantly reposition your feet as happens with platform pedals.
As mentioned already in this thread, flip-flops are a bad idea. In fact they are a spectacularly bad idea and I only found this out after meeting someone that broke their ankle from riding a bike with flip-flops. What happened was that the flip-flop bent round the pedal to be close to the ground, this hit some scenery and the hospital ward followed thereafter.