My upper limit is about 85 - 90 degrees which in Albuquerque, NM limits daytime riding for about 4 months out of the year. It is not so much the temperature itself that limits me, but the correlation between temperature and the evil, yellow sun which at a mile above sea level is like a microwave.

I will happily ride in 20 degrees. I have been warm riding in the low teens but I have never been cool riding in the high 80's+

bf