The new stores — 15 in New Jersey and five each in New York and Pennsylvania — expand STS's network to 150 stores.
The dealership's grand opening/anniversary celebration will run June 7 through Aug. 3 and include a "true fan" sweepstakes for prizes such as tickets to New York Yankees or Giants games, sets of tires or oil changes for a year, iPads, gas cards, etc.
STS will stage week-long grand opening celebrations at each store throughout the period. A schedule of openings is at www.ststire.com/grandopenings.
"Especially in these trying economic times, we definitely have reason to celebrate our growth," STS President Bill Caulin said.
"As an employee-owned company, we know that it's imperative to provide each and every customer with quality service. We are truly grateful that we've been able to serve our existing communities for 55 years, and we look forward to servicing these new communities with the same level of care."
STS said its "ambitious growth strategy" of the past year added millions of dollars to the local economy in the form of expenditures on construction and renovations on many of the new sites.
STS was founded in 1958 in Somerset County, N.J., by John Apgar Jr. and has been employee owned since 1984.
With 150 stores and more than 1,000 employees, STS is considered the sixth largest independent tire dealership in the U.S. It is an Official Partner of the 2014 Special Olympics USA Games.