I think the best deals was backfire inner tubes x4 for $11 back around Xmas. I'm not familiar with amazon. This is what I found. 2x $12 . I heard they are a little tight and may pinch with stock plastic hubs but you should have the metal hubs. Don't know if you want to try 200x50 tubes. https://www.amazon.com/Inflation-Pneumatic-Scooter-Trolley-Wheel%EF%BC%88inner/dp/B07GWFPMNZ