Their name—REO Speedwagon—comes from a 1911 fire truck chassis designed by Ransom Eli Olds, but for 13 years and 11 albums, REO's career had so many false alarms that the band seemed destined mainly to extinguish little else but themselves.

Then, unexpectedly, came Keep On Loving You, their now-ubiquitous rock ballad that helped the LP Hi Infidelity take over the No. 1 spot on the charts and become their first double-platinum success. "That's a precious metal," quips drummer Alan Gratzer, "we'd heard of only vaguely."

When the Chicago-rooted rockers—lead singer, guitarist and composer Kevin Cronin, 29; lead guitarist-composer Gary Richrath, 31; pianist Neal Doughty, 34; bassist Bruce Hall, 27, and Gratzer, 32—returned home last month, they broke the Rolling Stones' International Amphitheatre record by selling some 50,000 tickets for four shows in under four hours. One local diehard was hardly shocked. Millie Cronin, front man Kevin's mom, known locally as "Mother Rock" for scolding record retailers whenever REO bins are allowed to thin out, gloats: "It's about time the rest of the world caught on."

Faith in REO paid off, and her son's breakthrough song was about real-life faithfulness, or more specifically the lack thereof. "It was the most painful song I ever wrote," says Kevin. "I found out about an affair of my wife's before we were married and was angry and hurt. But I decided I was going to keep on loving her—that was a lot harder than saying, 'Hey, baby, take off.' "

Cronin isn't alone. Richrath had a similar problem with girlfriend Debbie Mackron and vented his wrath with Take It on the Run and In Your Letter. "Believe me," adds Gary, "it caused plenty of trouble when the girls first heard the songs. The girls had thrown it in our faces and we threw it back."

Denise Cronin, for one, wasn't flinching. "They should have called the album Wives on the Run," she says. "The band gets all this sympathy and is excused for all that goes on when they're on the road. No one," she jokingly pouts, "even mentions the problems of the wives who are home alone."

Fidelity to fans is a far simpler matter for REO. Long respected as a high-intensity grind-it-out road band, REO softens up along its itinerary for benefit basketball games with DJs. "We pick the short ones," notes Gratzer. Proceeds go to favorite charities like drug rehab and orphanages. "Young people," Cronin says believably, "kept us alive when our sales or hype didn't. Now we want to give back something to kids who need it."

Cronin, the son of a pension plan consultant father and social worker mother, grew up in Chicago sensitized to those sorts of needs. After his birth his parents couldn't have other children, and they adopted a younger son and two daughters. Kevin filled the house with his electric guitar chords as a teenager, and dropped out of Loyola University after a year to be a full-time rocker.

In its earliest incarnation REO played Illinois animal-house parties and small clubs, and once shlepped all the way to Connecticut to cut a disc and ended up making a pimple-cream jingle for $100.

But after two albums, the band's general complexion still seemed far from smooth. Cronin was axed in 1973. "We had huge ego problems," recalls Richrath, "and I was convinced we needed to get rid of Kevin. We were both immature."

He was invited back in 1976 after Gary was inspired by "seeing Don Henley and Glenn Frey of the Eagles work out their ego problems in the studio. I got homesick for Kevin." A year later manager Irving Azoff flew the coop to devote more time to his highflying Eagles. Despite the shakeup, they rebounded with You Get What You Play For, REO's first of four consecutive gold releases before Infidelity.

Speedwagon may not have taken the fast lane to the top, but along the way its members all relocated from the Midwest to the L.A. area. Kevin, Denise, her daughter from a first marriage, Christian, 7, and their son, Paris, 3, live in Woodland Hills. Kevin's off-road interests include swimming and trips with the kids to Disneyland—though it can be stressful now that he's no longer in some Mickey Mouse band. "I spend half my time," he complains weakly, "signing autographs."

Certainly nothing Walt wrought could match Cronin & Co.'s dizzying ride up the charts, but mostly it's been pleasantly disorienting. "We are at a point," Cronin boasts, "where you hire accountants to figure out what to do with the extra money." It could be a chore because, as Kevin proclaims, "We won't be spending $1,000 a day on smack, and we already have all the toys we want."