An afterthought... Has anyone ever tried doing a 70 mile a day tour on a single speed? Again, I'm thinking RAGBRAI here so any advice or criticisms would be helpful. I think IOWA is relatively flat and I ride fixed most of the time on a bike that I think I could make comfortable for longer durations. I think I'd want to do it for the fun factor. Is it insane?

Around 25 years ago my wife and I rode a noteably hilly ride here in the St Louis area along with a fellow who did it on a fixie so it's obviously been done.

The terrain in Iowa is obviously quite different from the mountains of Colorado but don't expect it to be like eastern Colorado either. You can have miles of relatively flat or maybe rolling hills and then encounter a river valley with hills that, while they won't be nearly as long, will be just as steep as the mountains.

The first person to tour the world did it on a single speed.

Reinhardt bicycle
Catalog #: 311,533, Accession #: 148,650
In collection
From the Smithsonian Collection
The donor, Fred A. Birchmore, a resident of Athens, Georgia, bought this bicycle in Gotha, Germany, in July 1935. An "Original Reinhardt," it was made by Fahrradfabrik Otto Reinhardt, Bielefeld, Germany, and was bought for 67 reichsmarks. In the course of the next two years Mr. Birchmore rode it through western Europe, eastern Europe, Crete, Cyprus, Egypt, Iraq, Iran, Afghanistan, India, Siam, Indochina, and the Philippines, before pedaling his bicycle home across the United States from California.

It has been estimated that his travels covered approximately 40,000 miles, of which about 25,000 were on the bicycle, and the rest by boat. Approximately four saddle covers and seven sets of tires were worn out during the journey. The present tires were purchased from a shop in Calcutta, India.



Link to the Smithsonian's article

It's perfectly doable fixed, even on hilly rides, as long as you're geared properly.

I've heard from several people who've ridden RAGBRAI that Iowa isn't nearly as flat as most folks think it is, so keep that in mind in terms of gearing-

I ride fixed most of the time but a Single Speed Chunker in the winter.
I would say gear the Single Speed about 2-3 gear inches lower than
the fixie. I like the fixie better but I really do enjoy bombing down big
hills (a lot of them aroung here) and regrouping.
I am part of a Fixie mailing list that a few people on it did RAGBRAI. There
stories were great !
I dont see any reason why you couldnt do a 70 mile day with no problem at
all if you were geared right.

Yeah... I feeling like if I do it I could just roll the flip flop hub so that if I'm feeling really tired I can just flip it so I can coast. I guess my fears are more about being able to keep up with my pack of friends (all non cyclists) and not totally conking out so that I can't have fun at night. Again, I ride a lot but I am just a little fearful. If I rode my fixed gear though I wouldn't need to worry about rack and panniers because it is already set up that way, it is an older "touring" bike so the geometry is a little more relaxed, and I'm accustomed to riding her all the time.

I hope my memory is correct, but if yu google
'Kent Peterson, Great Divide' you should get some
tales of this guys waaaay serious, zillion mile single
speed ride. I read some of it in an old Dirt Rag magazine
and it was a great sory and very informative about stuff you
might run into on an SS run.

You decide. Here is Kent Petersen's account of his fixed gear ride from Issaquah, WA to Cloquet, MN, June 15-26, 2002.

The Northern Road to the Interior

My LBS told me about some cogs that fit together so it's possible to have two on one side of the hub. If you hit some bad hills, you could manually change gears. Or carry a cog or two with you and swap them out.

Since you are accustomed to riding the bike you know what you're getting yourself into. You may want to map the route on one of these sites that'll give the elevations and grades. Maybe find some local hills that match the ones on the route and see how well you do.

Look up the Furnace Creek 508. Its been done many times (and completed) on fixed gear bikes. I have ridden my fixed gear 30 miles or so, and plan my first century ever on it this summer.

70 miles on a fixed is no biggie if you are in shape and your gearing is right for the terrain, especially if you have a flipflop with a bailout freewheel. Given that your friends are non cyclists as you say you should have no trouble keeping up with them. If anything they will be the ones who will be suffering. But why not just go out on your fixed bike for some longer rides and see how you do? I think you'll be surprised.

Surly has a cool 'Dingle Cog' too....
Two cogs together on the fix side so
all you have to do is move the wheel
forward and backward to change ratios.

No offense but that sounds like a solution that creates more problems than it solves. Changing cogs mid ride? Just roll a flip flop and you'll be fine. Or really take a geared bike.

See Sheldon Brown's pages on his single speed mtb, with a double chainwheel and a two-speed freewheel.

https://www.sheldonbrown.com/singlespeed.html

It would be nice to have a second granny combination around a 1:1 ratio, but using same chain length, for long climbs with gear. The Surly dingle cog looks nice, but the ratios don't seem very different to me. Can you choose different cog/chain ring combinations?

But, I think op would be fine in Iowa with single speed. Expect rollers, though. Iowa is not flat in most parts, it's not central Indiana or the plains.