RideYou could ride your bike without a shirt. This provides some advantages:
Less clothes overhead when on multi-day trip. One of my friends carries 5 t-shirts on each multi-day hike. That's more than a kilogram.
The ultimate evaporation - unmatched by any clothes. Furthermore, there is no clothe, which the backpack to press against the body and increase sweating.
Unbuttoned shirt serves the same effect, even better. The wind creates vortex in the shirt and cools even better than when naked.
Of course, there are some downsides:
- Some people are uncomfortable showing themselves or watching others do it.
- If riding all day in the sun, severe sunburn is a sure thing.
- Marginally lower protection in case of a crash.
- Only usable from about 15 C upwards.