Merlin walking 4-10

Merlin has more energy and is doing much better, but still only up to about two blocks- partly because he runs for the treats and wears himself out! He's using the K9cart with front extensions. The original owner of the front-extensions replaced the wheels with pink skateboard wheels, which work well, but I'm wondering if we can find something slightly larger, say Razor scooter wheels, to fit. I'm going to have to go on a mission and look for them.

The front wheels for all the various carts have issues. These are nice in the way they attach, permanently, so the dog is put in and out of the cart without removing the wheels or having them get in the way. But the wheels are small and the framework holding them quite heavy, and it would help to have more support for the corgi's front than a single band about 2 inches wide. For a female you can put a wider band in but for a male this would tend to block the ability to pee.

Doggon has better swivel wheels, but a bulkier way of attaching them to the cart, and my dogs aren't used to the Doggon-type cart. (Though Wesley did fine in his.) They also sit wider apart which could be an issue. And Eddies Wheels has non-swiveling front wheels that are a pain to attach to the cart.

What I'd like is partial swivel, so they could turn but only about 45 degrees, allowing wide turns but not ending up sideways (I've never seen a swivel like this.) A lighter framework might also be nice. I like the looks of the K-9 East front extension a little more; it seems like it would be lighter. I need to ask them how hard it is to add and remove from a standard cart. K9 West was an easy do-at-home modification.

What I'm after is wheels that allow a dog to move on rougher terrain than the sidewalk seen here.