I'm an anthropologist, I work in the UK and Ireland. Given Covid concerns for this summer I don't think I will be able to rely on public transportation as much as I did in previous dig seasons. I'm hoping for some advice on a decent steel folder that I can throw a rack and pans on and that can take up to 240lbs. I'd like to be able to fold it up and take on a plane, train and fishing boat/zodiak easily enough.

i was looking at Citizen bikes since they have steel frame options and DaHon. Any other recommendations?​​​
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The folders are complicated because of the folding. They have proprietary features and must be build to high precision. Hinges and clamps increase weight that works against portability. The market is smaller than for regular bikes. With all this, you need to be prepare to spend more than for a regular bike when staying within similar quality expectations. Yes, there will be many circumstances where a budget folder will be easier to handle than a regular bike, but you will not be able to check it in as a regular luggage on a plane and it may be difficult to tackle even on a train. You need to be realistic.

Do you plan to pack the bike in a suitcase gif travel? Are you looking for a particular wheel size? Is speed or hill climbing a priority?

I'd like to keep the budget under 1.5k if I can. I'll be on mostly flat ground in post glaciated areas with decent paved roads. Wheel size 16"-20 and oversized luggage is fine since I have to check most of my equipment as oversized luggage anyway. The problem I have run into with my standard bike is that it takes so much time to ship and then have it built up at a local shop and then take it with me on the ferry which just wasnt a possibility in Shetland and the Hebridies.

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See if anyone is selling a Bike Friday anywhere near you. Designed for packing in a suitcase, rides great, uses standard parts, no hinge.
Even if you find one somewhere else on the continent, they can ship in the suitcase to you for a reasonable price most likely.

Have you lookded at Brompton or Bike Friday?

I have 3 folders: Bike Friday New World Tourist, Dahon Boardwalk type and Brompton. I have been taking along all 3 in connection with work as means of local transport. All are steel. Of the 3, only Dahon would fit, and in fact quite well, into your budget. However, it is extremely klutzy in handling. I take it only on trains to destinations that are easy. Bike Friday takes a lot of time to disassemble and assemble. Only Brompton is of the type where folding or unfolding is completely uneventful and air transport too. The weakness of Brompton are limited gears. However the costs, including bags for transporting the bike and for carrying loads on the bike, take costs above 2k$. Pakit, that linberl has, might be a similar option but for a similar cost.

Basic pakiT is about $1300 but if OP is in England, ordering from BF with shipping and customs is not going to work well. However, NWT Bike Fridays do come up for sale over there, I see them on the BF Facebook page and the Yak from time to time. Knocking down a NWT for suitcase travel takes about 20 minutes once you've done it a few times. It's not hard, and there are videos to help with the process. While I do love my pakiT, I would suggest a 20" wheel for most folks in England - the 16" wheels do not love cobblestones and bad streets. Furthermore, it's easier to find 20" tubes/tires than it is 16" (even in the U.S.). And, yes, I know Brommies are 16" and they are English but I also see a LOT of Brommie posts about suspension add-ons, lol.

I have done it tons of times and it takes me about 2h pretty consistently. It is the last thing you want to do after a long travel. If you have some sort of bare bones bike that's not useful for nothing from my perspective, you can run some sort of exercise for UTube, but I am talking about my normal life. I also have a Brompton with all kinds of similar complexities and it takes maybe 7 min for about the same goal.

Well, when I had my NWT (1x11) I did it in less than 30 minutes even after not doing it for months. Don't know what to tell you. I also have friends with NWT's who can do it faster than I. Split handlebars helps. I did have the color packing process photo chart i made (mostly for TSA) to help me remember. I guess we move at different speeds.

I am in the US (Everett, WA). I have looked at Bike Friday and DaHon but the REI didn't have any Bromptons when I went in last. I have ridden a few Dahons and found them a little clunky, but my bike shop didn't stock many models and mostly for the boat camping crowd. Weight is in an issue for me only when it gets above 35lbs. I dont need a huge range of gears because it's pretty flat ground where I work. I was thinking 6-7 speeds would be sufficient. Rider and load weight though is more of a concern. I tip the scale at 235lbs with my backpack and wet weather gear and that's before I get on the bike.

The important Brompton dealer in Seattle is Electric & Folding Bikes NW. I think they were one of the two first dealers in the US, though presumably under different ownership and name then. They normally kept 1-2 Bromptons on hand, even when there was a shortage, for the customers to try out. Give them a call. Montlake Bicycle was fine too in my memory, but I would start with the shop above.

Thanks! I'll check out Electric and Folding Bikes this weekend.

IMHO, best bang for the buck is Downtube.

Which ferries are giving you issues with a full-size bike? We had no troubles getting to Mainland Orkney from Aberdeen a few years ago, or booking them on the trains to there - including with a trailer and camping kit.

I had trouble with the Mull ferry which can take between 4 and 6 vehicles depending on size and we're packed in pretty tight. The passenger seating area is very narrow and bringing a fullsized bike inside would have been a significant impediment to getting to the safety exits. Bike had to stay on the car deck and there wasn't a secure attachment site and the transportation guys didn't want it locked to the boat. I also had issues with some of the smaller island ferries like Musa, Fair isle and Isla. Some of the boats we have to hire and they are essentially small fishing vessels, or as we called them "Shetland Uber"

Dahon Mariner,...it come's w/rack an fenders, can hold 250lbs (more actually, but for legal reasons they cap it at that weight), and comes in either the i7 model (7 speed internal geared hub), or D8 (8 speed w/derailleur). Look for the model that has the Deltec cable and Jaws tech folding tech. It's the newer model. It's about $750ish here in the USA. Great bike for travel,... I have the i7 model.

A 20" Dahon with racks, eg Mariner (Al frame) or Speed D8 (steel frame) sounds like a reasonable compromise and not too expensive an experiment if it doesn't work out. Bickerton (I think Al frame) fills a similar niche in the UK, although only the brand name is original. I recommend getting one that has the luggage bracket welded to the frame in front of the head tube as that increases your luggage options a lot.

A Brompton is better for multimodal transport as its fold is much smaller but may be a bit compromised on the tracks that your job likely takes you down.

I have taken my old Dahon Speed down some pretty rough terrain on touring tyres. Not too fast though obviously.

My boyfriend ended up ordering me a Citizen Tokyo with a rack and muffin tires for Christmas so I guess for the short-term we'll see how it handles. One of his friends weighs 264lbs and doesn't have a problem riding his citizen apparently. It should give me some time to save up for something more substantial in the future. Though I like how quickly it folds down. That's great for getting on and off the boat and or train and quickly get moving.

Their website indicates that these tires are airless. I rode such tires on share bikes and, within the general low expectations regarding such bikes, they were acceptable there. However, I would not want to such tires on my regular bikes. Still, technology moves and might improve. It would be good to hear how they work for you.

Yes will be interesting to hear what you think of the muffin tyres. Let us know how you get on.

When you are using this folder, considering that you have a Trek 520 touring bike, you have the extremes, an ultra portable bike and a long distance load carrier. That gives you an opportunity to figure out what your priorities are in a folder for doing field work.

Lots of folders could be easily loaded onto a small boat. Some of the bigger folders would not be convenient to carry into passenger area on a ferry where smaller ones might be.

And some of the folders would be easy to pack for airline travel while others would be similar to packing a full size bike.

My point is that there is a huge range of folders out there, but once you use one for a bit, if you are unhappy with it, you will have a much better idea of what you really want in a folder.

While you are in the UK, if you decide to buy a bike locally there, make sure that they can help you get the VAT refunded as soon as you leave the country. And if you bought a new bike there and used it some, then brought a used bike back from the UK that you bought there, being used instead of new would reduce the value for purposes of paying any customs duty upon arrival here.