Say from a 20 inch folder.

The front wheel would be relatively easy, just switch out the fork, but what about the back wheel?

What frame are you modifying? It would make all the difference in the world. I have seen it done to Raleigh Twenty but it looked odd to me the way he did it. Roger

how many tools do you have in your home shop ? brazing cutting and all that .

just changing the fork drastically changes the steering .. easy rider chopper your goal? ..

It would not be easy to put on a rear 24" wheel on almost any 20" folder. Changing on the front only isn't the best idea either.

Regardless, why would you want to?

1. see very few 24 inchers
2. could fit more easily on airplane than 26
3. i've ridden a 20 inch before and I did not like it much at all. Hopefully, 24 would be better and close enough to a 26

Just speculating. I figure that some frames could likely handle it (just 2 inches) while others cannot. Big thing would be brake braze-ons, to which it looks like disc brakes are the only way to go. Or just putting brakes on the front and relying on a coaster brake.

You'll get worse tire selection with 24" wheels. And unless you're riding off road or on really crappy roads, there isn't much advantage to 24" compared to 20" wheels.

20" don't ride that differently. You didn't like the bike on which the wheels were mounted...

considering that a 24 inch Tern Node d8 is 750 all built up and ready to go, it doesn't make sense to make a monsterbike which doesn't work cause the geometry is all wrong

here is an example
https://www.thorusa.com/tern/noded8.htm

1) maybe there are good reasons for that (i.e. not enough more compact than 26" or 700c to make it worthwhile). But they do exist and would probably ride much better than trying to shoehorn bigger wheels into a frame not designed for them.

2) Even 20" folders usually require some disassembly to fit in standard luggage that's compatible with airline size limits. I'd expect a 24" version to require considerably more effort and likely special luggage that's more likely to raise questions at the airline counter even if it does eventually pass their tape-measure tests.

3) Probably a characteristic of the particular bike you rode. My 20" folder's handling characteristics actually fall in between two of my 700c road bikes (one is a quick handling crit-bike, the other a touring-oriented bike). The smaller wheels are a bit harsher with the same width tires, but using slightly wider tires eliminates that issue. And rolling resistance is marginally greater, but this is pretty insignificant anyway at normal cycling speeds. And I'd be concerned about the variety and availability of good 24" tires in comparison to 20", 26", or 700c.

Plus Airnimal out of UK is made around 24" wheels if the wheel size is paramount, just buy one.

I rode the tern eclipse x20, its fantastic!

On a Raleigh 20 you need to remove/move the rear seat/chain stay bridges and get a longer fork.
Makes for a nice - and cheaper - ride than an Airnimal.
Mine is running a 7 speed Shimano 110 gruppo. Have brazed new stays in since this pic and it's nice bbq matt black instead of hot-rod primer grey.