Seems like most people start in May, but whats the latest date any of you have completed the Trans Am route east to west? I feel like this is the year for me to do it, but wouldn't be able to start until August 1st.
Hopefully others who have started later will comment, but my impression is that it would make more sense to go west to east if starting late. You are likely to find snow on the passes if starting in the east and going at an average pace. It isn't rare for Mckenzie pass to close for the season in October (you can detour to Santiam pass, but still...). Snow is fairly likely on Hoosier Pass in September.
Assuming 9-12 weeks for the trip I wouldn't want to start in the east on or after Aug 1. Starting in the west Aug. 1 is about as late as I would start.
On my first cross country tour back in 1987, I started from Astoria on September 1 and got to the Outer Banks of NC in early November. I didn't do the Trans Am - but approximated it. I would say that it got a little bit iffy after October - the days just got so short. Halloween was in Blacksburg, VA - I remember. I had glorious weather across the West, snow in Lincoln, Nebraska, and quite a few yucky days in late October. I would say you could leave as late as August 15 for a planned 10-week tour. Then allow yourself a day here and there later in the tour for bad weather.
Fall touring is fabulous - just remember the days are short and bring something to read in your tent.
I started from Astoria on September 1 on my first cross-country tour back in 1987.
Ended on the Outer Banks in early November.
Great Sept weather. Snow in Lincoln, NE in early October. By late October it was getting iffy in the Appalachians. Come November the days are getting awfully short.
I think you would be fine leaving from the West as late as August 15. With the record warm falls we have been having (global warming?) I suspect that Sept 1 departure would be easier now - although the length of the day won't change no matter how warm it is.
Fall touring is fabulous -
But bring stuff to read on those long nights in the tent.