I'm hoping the OP isn't opposed to changing per se, but he may not have access to a shower and he doesn't want to wear spandex. Some people don't like to wear spandex and that's fine. There are plenty of alternatives that would be cooler than typical business casual clothing.

In the summer I don't wear long pants if I can avoid it. Being outside in warm and humid weather it's hard not to sweat in business casual attire even if you aren't on a bike. Inside a climate controlled environment is a different matter. Different clothes for different environments makes sense to me.