Last Sept and early OCT. I rode my 2013 C-5 from San Francisco to Washington DC via the old Lincoln Highway. Not a wise choice given how remote the western section is. But the traffic is very sparse and the small towns friendly. You can get lost as some (a lot) of it has been incorporated into modern roads. Get the Lincoln Highway Association maps. Chicago was evaded completely. The bike has the original "0" ring chain, a new higher quality battery (the old one was fine)and the battery cables replaced. Bike has the RE stage I kit (with baffle installed) and 7inch sealed beam headlight kit. Never rode at night. The engine was broken in with 1500 miles on it with three oil and filter changes. I put in a new NGK spark plug and a small kit on the back and left. I traveled 300 to 350 miles each day. 150 morning and 150 afternoon. Speed was 55 to 60 mph. No more. Stayed in motels, no camping. Chain took two adjustments along the way. Did one oil change along the way. Waited out the rain when it came if I could. Original Avon tires were fine. No flats. No problems what so ever. Nothing. Nothing fell off. The exhaust header is still the same as new with no bluing. Solo seat is not so great for long rides. It was the limiting factor some days. Why do it? Because Route 66 is done too many times and the Indians do it all of the time in India (south to north to the big mountains and back) and they have the same results on REs. These are good bikes; if you ride them as they were designed to be ridden. Never ran out of gas, but came close once or twice in the west. The Aerostich padded under wear is the best investment you can make. Bought two pair. Did not do a return trip. Trucked it back as I ran out of time. I will ride the length of the Rockies next, from Santa Fe, New Mexico to Canadian border in June on the same bike.
http://modernvespa.com/forum/topic134424. Here is link to a good video on the Lincoln trip.