Lloyd Carr’s retirement after 13 years as head coach — and 28 overall — at the University of Michigan marks the end of an era at college football’s all-time winningest program.

Since 1969, Michigan has been coached by Bo Schembechler or one of his former assistants. Even if athletic director Bill Martin opts for someone with school ties like LSU coach Les Miles, the presumed frontrunner, the winds of change are blowing in Ann Arbor.

Despite playing on TV more than any other school not named “Notre Dame” and filling in the largest stadium in America, Michigan has trailed some of its college football contemporaries in the race to turn the sport into an ever-bigger business.

The massive stadium contains no advertising. While the school was among the first to sign an apparel deal with Nike, it also had the sports clothing giant de-emphasize the omnipresent “swoosh” in a subsequent uniform design. Carr is well compensated, but much less so than some of his peers with far-thinner résumés.

Those who would assume Carr is being asked to retire or being nudged aside in the wake of his sixth loss in seven tries against Ohio State don’t understand the dynamics of the Michigan program. Had Carr insisted on returning next season, he would have. Martin has made it quite clear that only Carr would determine his fate. Furthermore, Carr’s decision has been in the works for some time — he altered his contract last offseason in a way that strongly suggested this would be his last year on the sidelines.

Among major programs, Michigan has always been tortoise rather than the hare, and in doing so has avoided the boom-and-bust cycle that has beset nearly all of them. Michigan has not had a losing season since 1967 and has played in a bowl every year since 1975 — also the last year the Wolverines had a home crowd of fewer than 100,000.

Carr is a big part of that success — he won or shared five Big Ten titles and took Michigan to four Rose Bowls and an Orange Bowl. He retires with a .722 winning percentage, seventh among active coaches, and the school’s only national title in the last six decades. More important to Martin, Carr’s teams have never been touched by scandal — which carries considerable weight at a school whose high profile basketball program was laid low by “Fab Five” era misconduct.

Still, Martin is a businessman. Under his stewardship, Michigan’s athletic department has embarked on aggressive revenue-growth initiatives. He is about to oversee an estimated $250 million renovation of the stadium that will accent the classic bowl with premium seating. He knows he cannot afford to see the program sink as traditional powers Nebraska and Notre Dame have. As a result, every top coach in America will be on Martin’s list.

Jobs the caliber of Michigan don’t come open often. In the insular world of big-time college football, Carr’s retirement is likely to set dominoes tumbling, perhaps all the way to Louisiana — where Miles will be under a siege until he is either hired by Michigan or officially no longer a candidate.