If you are 20, your father is 40 - 60, probably, and your grandfather is 60 - 100. Most genealogy data on th eInternet is about people born before 1900. You might try asking your grandfather who his parents were, especially his mother's maiden name. That would be a help. If he knows where they were born or even lived, it would help too.
The place most people start is the Mormons; http://www.familysearch.org/Eng/default.asphttp://www.familysearch.org/Eng/default.asp they just recently put the 1880 census on-line. There are 14 people surnamed Uhr in Pennsylvania on it. There are over 284 citations in their general search for Uhr. Some go back to the 1700's.
You might consider interviewing your grandfather about his life; once he's gone, you will have lost a generation of knowlege.
Finally, the GTE people pages http://wp.superpages.com/people.phtml?SRC=http://wp.superpages.com/people.phtml?SRC= have 13 Uhr listings in Pennsylvania. Call th eones you don't know and ask. If they are a second cousin and have done research, they might share it with you.