Originally Posted by
Iride01
When you inflate the tire to the pressure you ride at. If the cut pooches out like a grandma wanting a smooch from her grandkid, then sure, you probably ought to replace it. Especially if the tube can be seen bulging out as well. Assuming you are tubed.
To put it more clearly, if the tire bulges when inflated, then the casing is damaged. Some would boot it at that point, and others would throw it away. If there is no bulge, then there is no reason to not use the tire.