Properly flexible filaments are hard to do with the bowden printers, as you are essentially trying to push a wet noodle down a drinking straw and you struggle to get enough force at the hot end to drive the material thru and flow properly.
I have a direct drive printer which I've set up specifically to use TPU - that gets around the feed problem, but the other down side is the print speed is still low. The realy soft (80 shore hardness) material I started with could only print at around 15mm/second, which translates to a single tyre for a CCKW taking 8 hours.
I've since moved on to another brand, which is harder at 85 Shore but that allowed me to crank the speed up to 25mm/sec and get that tyre done in around 5 hours. Its also a about a quarter of the cost of the really soft material as well.