The lack of tire availability is really a question for the industry as a whole, as the folder market is too small to exert enough influence to make a change.

I have a 20" folder (Zizzo Liberte) and a 20" 451 folder (Bike Friday Pocket Rocket). When ridden side by side, the compromises of 20" wheels are pretty clear. And while the Bike Friday rides 90% like a 700c bike, when I get on my 700c bike, the differences are there.

The question for the industry as a whole is, why the obsession with 700c? Anyone riding a 700c bike and with an inseam of 30" or less is riding a compromise of odd geometries and toe overlap. Mini velos and 20" folders are fairly popular in countries short on average stature for this very reason. I rode a 650c road bike for years, and it provided many of the rolling benefits of 700c with none of the 700c/small frame drawbacks.

It's within this context that I ask this question. Helix has shown - the precious few that actually got their bike - that nice rolling 24" folders can be made. It could be the Goldilocks size - rolls well and folds ok.

It's encouraging that ebike makers - faced with new packaging challenges - aren't as dogmatic (700c or bust!!!) as the rest of the industry with respect to wheel size. 20" wheels are popular for electric cargo bikes, and 24" and 26" options are also widely available too. Perhaps the ebike market - one of the fastest growing in the industry - will spur Schwalbe, Continental, and others to provide a greater variety of quality tire sizes that folder makers can then choose from.