The C-Tug Kiwi Wheels are puncture free solid plastic wheels that will retro fit older C-Tug Carts that came with the pneumatic wheels.
I like them. Replaced the pneumatic tires on my two C-Tugs because I never really trusted the tires to hold up on a longer tow. The KIWI wheels fit with no problem and work well. These wheels do not flex, so the "ride" is a bit rougher than with the old tires and the resulting vibration may result in a bit of loosening of the strap over the kayak in a longer tow over rougher paths. Not really a big concern, but be aware. On the other hand, the wider footprint of the KIWIs makes pulling the cart over uneven ground slightly easier. Have not tried them in sand but suspect they will work better there also.
I had the tube tires and they were okay but it was all but impossible to get a chuck on the stem to put air in them. I shopped at a retail outlet for these wheels and they thought they were gold. ACK, Fair price and quick delivery. All problems solved.