ETRTO507 (there are several other 24" sizes, ETRTO520, ETRTO540) was a BMX wheel size. There are plenty of tires but most of them are wide tires 50mm or wider.

Helix made a wrong decision when they decided to design a frame for ETRTO507 wheels with a max width of about 40mm.

Availability of high performances tires (not only low rolling resistance but this together with good grip, good puncture resistance, long lasting) is a key factor for any bicycle, there are none for Helix, only low end tires.

Helix is struggling with tires choice since almost the beginning of the project, well before any Helix bike was delivered.

The project was supposed to deliver a lighter (because of the titanium frame), smaller, safer, cheaper bike than any existing folding bike. The project failed in all of these 4 aspects:
- The helix frame is heavy because if its complex folding mechanism. Titanium didn't help. As consequence, even with lightweight components, the complete bike is not really lightweight.
- Its not smaller than a Brompton or Dahon Curl.
- Its not safer, no difference in safety compared to other folding bikes.
- Its not cheap, Helix could never reach its target manufacturing price. It costs more than twice its target price.