repair
I know you've seen these things. It's an indestructible black fiber-plastic cart body and a pair of 20 x 2.125 inch wheels with plastic spokes.
Does anyone know if I can replace the tires with the same size bicycle tires with tubes on the original wheels? Hate to throw out the wheels which also are shaping up to be indestructible (but not the tires).
You could try some Fix-a-Flat. If nothing else, it might show you where the leak is.
Pump the tires up and apply some soapy water to them, or hold them underwater in a large bucket. This will help you locate the leak(s).
If the leak is in the tread, you could try a tire repair kit like this
If the leak is in the sidewall, you'll have to replace the tire.
If the leak is near the rim (and the rim is not bent), remounting the tire might fix the problem.
I think that's a good idea, but you dont need to use concrete like the quikrete bags with big rock, make your own using portland and sand, and adding the glue will help!
Best Answer
I have 2 of these on my farm, we used mountain bike tires on the one that broke. We thought the wider and heavier rims would be needed even though we only carry sawdust for bedding stalls I think they have been on for 3-4 years and we did change the tubes that came with the rim & tire to the thorn resistant after a couple of flats.