Wheel Diameter, Wheel Width, and Tandem Wheels
The outer diameter of a caster wheel affects how easy it is for the caster to be able to move across rough or irregular surfaces. Large diameter caster wheels are able to bridge wide gaps where a small caster would fall inside and get stuck, such as the gap in the floor between an elevator door and the elevator car.
However, the larger diameter a caster wheel, the higher or wider the caster support arm must be. Either the base of a low-hanging object must be lifted higher above the wheels, or the casters must hang out to the sides straddling the low-hanging supported object. Large diameter swivel casters also typically need much more room to rotate the vertical shaft than a small caster.
Load capacity may be increased by using wider wheels with more ground contact area. However, when rotating a wide swivel caster in-place, the center part of the wheel-to-ground contact patch rotates slower than the regions further out to the sides. This difference in rotation speed across the base of the wheel contact patch causes wide wheels to resist rotation around the swivel, and this resistance increases as weight loading increases.
An alternate way to increase load capacity while limiting swivel-rotation resistance is to use multiple narrow wheels in tandem on the same wheel axis. Each wheel has a comparatively narrower ground contact patch than a single wide wheel, so there is less resistance to turning in place on the swivel.
Read more about this topic: Caster
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