If your wheel has a crossbar it isn't glider safe. Crossbar wheels act like scissors on glider tails and can cause not only the fur to be pulled out but tail injuries than can and have resulted in tail amputations.
Most pet store wheels are not glider safe I'd suggest removing the wheel and watching the tail for any skin coloration changes, if the tail skin gets dark-black in color the glider needs to go to the vet.
Glider safe wheels can seem expensive at first but they last a long time and they are considerably cheaper than vet bills from unsafe wheels.
Safe Wheels... Atticworx has some really great wheels, personally I love the xmount as it's the easiest to put in and remove for cleaning than any other glider safe wheel out there
http://atticworx.com/
This my 2nd fav wheel and first for customer service and quality of materials. These wheels are awesome and are the only ones that use a coated metal mesh track on every single wheel and only wheel with bounce. The quality of materials is unsurpassed.
http://customchoicecruiser.all4gliders.com/
The Raptor wheel was my first wheel, I bought it like 4 yrs ago and it's still in use with little wear n tear signs. It's a great wheel but can take longer to receive than the others above.
http://www.mygliderwheelsandmore.com/
Fast track also makes a decent wheel... I've never had an issue with it either.
http://www.spinzoneglobal.com/
I personally have at least one or more of each of these wheels. They are all quiet, durable, and long lasting when cleaned properly and mounted properly.
When mounting a glider safe wheel please make sure there is enough clearance around the wheel it should be at least 6 inches off the floor and below the roof with room on each side of it to prevent gliders riding on the outside of the wheel any injuries...... yes it does happen.