A lot of small animals require a wheel. But do rats need wheels?
It depends on the rat. Some rats won't even touch them, but other rats LOVE their wheels. If adopting from a rescue you can ask the staff if the rat you are adopting uses a wheel. If you don't know provide the rat with one anyway, because if they do like the wheel it is a great way for them to get exercise. If after a few days they don't seem to like it, you can remove it from the cage, but keep it handy in case you want to try again, or for if you get another rat that might want a wheel.
When looking for an appropriate wheel here is what to look for:
A solid surface
Mesh wheels or wheels with rungs can potentially cause injuries to the rats tails or legs. Also a solid surface wheel is easier to clean and they don't squeak like the metal wheels.
Bigger is definitely better
Make sure the wheel is appropriately sized for a rat. Look for a diameter of at least 11 or 12 inches. Anything less is best suited for a hamster, not a rat.
Some good wheels:
Super Pet Comfort Wheels: These are great, albeit a little noisy. Make sure to get the largest size.
Silent Spinner: The largest one is great for rats, and for you because it is SILENT! (it really is silent, it is amazing!)
Wodent Wheel: This is probably the best wheel for rats. It comes in two types for rats: Senior (which is great for older, smaller, or female rats) and Wobust (which is best for active rats or large male rats). There is also Junior which is great for young rats and hamsters but is too small for adults. This is probably the safest wheel you will find.
Note: The Wodent Wheel is only available online. Here is a link to one site that sells them (you can also find them at some other online stores, such as ebay and amazon):