If Craig Nicholls is the public face of the Vines, then Patrick Matthews is the Sydney quartet's public voice. While the diminutive Nicholls may claim the media's attention with his eccentric behaviour and erratic stage performances, he rarely gives interviews - especially once the band are on tour.

Enter Matthews. After a night out at a Munich beer hall, the bassist is sitting on the bed of his German hotel room, affable and low-key, well aware that even when Craig Nicholls isn't talking, he's still the main topic of discussion.

"The hardest question I always get is: 'What goes on in Craig's head?'" says Matthews. "The answer is that I really don't know."

Depending on his mood and the depth of his interview schedule, Matthews sometimes toys with the notion of asking the band's sundry publicists to place Nicholls and his actions on a blacklist of questions not to be mentioned. But midway through a European tour to support the group's second album, Winning Days, he's happy to field all queries.

The dynamic between the pair exemplifies the curious tension that underpins the Vines.

The band's 2002 touring schedule, for example, came to an unplanned and sudden end at a Boston show when a disagreement turned the stage into a wrestling arena, although it's now written off as the blow-out of stress and tiredness from excessive time on the road. Nonetheless, Matthews now discusses Nicholls from a distinctly Swiss standpoint.

"I don't have the charisma or the talent to carry off a band by myself, so you have to appreciate what Craig brings," he concedes.

"Most of the time, if he's doing stupid stuff - or what I consider stupid stuff - I can see how it's interesting to others. I don't condone it and I don't apologise for it."

There's no denying the grim edge to proceedings when the Vines - Nicholls, Matthews, drummer Hamish Rosser and rhythm guitarist Ryan Griffiths - play live.

Nicholls may change his vocal style from line to line in a song and then ritualistically attack the drum kit at the set's culmination, but the real source of intensity is Matthews. When he plays, it's as if he's trying to seal himself off from Nicholls and his antics, trying to project a barrier across the stage to distance himself from the discomfort he feels.

Did Matthews know what he was getting himself into when he allied himself with Nicholls and the Vines?

"Not really," he replies. "I used to see Craig just at shows and stuff, but when we made the first record we all had to live together, and that's when it became different. We couldn't avoid each other and there were these outbursts. So no, I didn't know."

Touring has only served to exacerbate Nicholls' behaviour and Matthews' unease.

"Being on a tour bus is like being on a submarine," Matthews adds. "There's no escape."

Perhaps it's put in stark relief for Matthews because of the choice he made when the Vines first attracted record company interest in Sydney in 2001. At the time, the bassist was coming to the end of a deferment in his medical studies, which he had taken after finishing the first two years of the demanding course. When events quickly escalated and the Vines were presented with the opportunity to record their debut album in Los Angeles, Matthews was thinking about his third year of learning, most of which would be spent in a Sydney hospital.

"There will always be this curiosity about what could have been," says Matthews. "I didn't really make the decision in the best way. I went along to the dean of medicine and said, 'Can you give me another year off?'. However, I'd been out pretty much all night and didn't look the best. I didn't have my wits about me either, so the choice was easy for him. He said, 'No, you can't have another year off - decide what you want to do'. In the end, I just let things drift along. On the subsequently finished it for use in the studio."

One of the criticisms of the Vines' new disc has been that many of the songs were rejects from Highly Evolved that shouldn't have made it past a strict editing session, a charge that Matthews is sanguine about.

"There are a few that are old - Rainfall, Winning Days, She's Got Something are quite old - but there are others that were ideas from when we did the first record, stuff like Fuck The World and Amnesia and TV Pro," he explains. "We had chords, but they weren't finished, we'd barely played them. They needed to be recorded properly."

Whatever the cause of the malaise, Winning Days has been a commercial failure in comparison to the worldwide sales of approximately 1.3 million copies that its predecessor accumulated. After just eight weeks on the Australian album chart, it's languishing at 75; the situation in America has been just as dismal.

But for Patrick Matthews, after all the choices he's made and the ongoing accommodation with his bandmate, the Vines have been about something more than purely commercial success. "When something like this happens, you become more confident in your ability to have an impact on the world," he concludes. "It shows you've got potential, because I never expected to be part of a successful band. So maybe there are other things I could do that I thought I never could."

The Vines play at the Forum, city, on Wednesday night. Winning Days is out on Capitol/EMI.