"Many people have asked us why we didn’t build a four-wheeled cart that wouldn’t need to be balanced. However, four wheels would double the rolling resistance and thus the effort required to push the cart. Furthermore, a four-wheeled cart is less maneuverable and more difficult to drive on uneven terrain. You also need to get two extra wheels, and you need to build a steering mechanism.
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I would have asked them why they didn't make a 3 wheeled version. Keep the two big wheels on the side, add a smaller freely rotating one in the front, like a lot of strollers have. They could make it just a tiny bit too low, so it's easy to roll it with both 2 or 3 wheels.
I have a 4-wheeled wheelbarrow/cart/whatever. I think Scotts made it, but I could be wrong (it's green with orange lettering); I got it at some big-box years ago. It's wildly easier to move than my regular wheelbarrow, precisely because you expend no effort balancing it, and it's equally easy to use pulling as pushing (even with kinda crappy small, hard wheels). It is definitely not as maneuverable as the traditional, but it's easier on (most, not all) 'uneven terrain' (again, I don't have to balance it) and it doesn't have any 'steering' other than pushing the handles so it points the direction I want to go (I do know there are more elaborate versions that have a steerable set of wheels; I got the cheap version).
I guess tl;dr: I dunno what these guys are going on about and wonder if they've ever actually tried a 4 wheel cart.
I would have asked them why they didn't make a 3 wheeled version. Keep the two big wheels on the side, add a smaller freely rotating one in the front, like a lot of strollers have. They could make it just a tiny bit too low, so it's easy to roll it with both 2 or 3 wheels.