SandwichShortOfAPicnic as I have no idea what your ages are, us, well, let's just say we collect Social Security
we have all the time in the world to just meander.
As the World has changed so much and violence is running rampant, in particular in the large Cities, as I made mention earlier, DH & I stay away from the majority of them, with a few exceptions.
We've done not only the parts of the original Route 66, but also the "new" aka I-40.
FUN FUN FUN!!!
As I recall, there's a travel guide of Road Side Oddities that I would encourage you to research as well.
I would suggest that you "follow the 70 degree weather" especially on bikes.
Do you plan on any "wild camping"? You can use your NPS pass for some of that as well.
Us, we aren't campers (I would have liked to have gotten an RV way back when, but...) we try to stick with one, maybe 2 hotel chains and earn reward points for free nights.
Our personal favorites are Best Western Motor Court type hotels and then Hampton.
BW (not the plus or premier) for the nice, firmer mattresses-no frills kinda place and also we can back right up to our motel room door, unload and reload with ease (ask for a first floor room).
Next is Hampton by Marriott. These are bit of a step up, nice room, great lobby area to hang out in, but for us, the mattresses are a bit too soft and we have a soar back the next morning. Yea, but the free hot breakfast is usually better at the Hamptons
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As you say, going from North to South along a coast and then East to West and back again across a country is what we've done, numerous times.
The USA has some very interesting history and gorgeous scenic byways, just depends on what you want to do. One of our most memorable road trips was our "Great Western Adventure" and "Florida Here We Come" both trips were over 6000 miles round trip, taking us about 30 days-give or take. Oh, did I say that we name our trips now to remember, "Oh yea, that's when we ..."
Can I also say, I (we) just LOVE to plan our road trips!
I wish I could sit down with you guys and point at this and that, no don't bother with that, this place has some of the best seafood, go to this diner over there, etc.
To me, that's part of the trip too.