I have had some problems more in the winter in Spinning, where you don't get the "aeration" you do on the road outside. My derm suggested a powder called "Zeosorb", you can get it at Walgreens but have to ask the pharmacist. It is a highly absorbent powder, much higher than baby or corn starch powder. It basically keeps the perspiration from cauzing havoc or creating rashes. Works well for me, I use it everytime I ride if I remember. Also good anytime on hot summer days.

They also make a miconazole version if you are prone to athletes foots, etc.