Best time of year to travel route 66?

September is usually nice everywhere.

...and so now is much of the old Route 66

I looked at the average temps there for a trip later in the year. Mid Sept seemed to be the best.

I have followed as much of Route 66 as can be followed in August, from LA to Saint Louis and it was fine. Yes we used the AC a lot.

During the summertime....!!

im a brit ..done the route 66 ..not worth the effort ...America has thousands of routes much better ...drive death valley ...corpus Christi to Brownsville ..taking in padre island

September is usually nice everywhere, and many of the tourists are gone by then.