Comfort Wheels from Super Pet www.petsmart.com - $11.99 (giant 12") Product Description: These silent wheels have a solid running surface to provide a safe source of exercise for your small animal pet. Plastic wheels feature smooth treads to allow for a surefooted grip while creating a comfortable, safe running surface. A versatile clip attachment allows the to be free standing or attached to a wire cage. RattyRat's Review: This wheel is completely safe for your rats. It is much easier to clean than the Wodent Wheel, but is somewhat noisier. We like this wheel a lot because rat poop doesn't tend to collect in it. It's our wheel of choice.