Black Rebel Motorcycle Club formed in San Francisco in 1995 in obvious thrall to UK indie icons such as Ride, Spiritualized and Jesus and Mary Chain. Indeed, so indebted were they to the Mary Chain's squalls of white noise that some unkind souls suggested their future could lie as a tribute band.

Their third studio album, Howl, released this week, sees BRMC perform a severe about-turn from feedback-laden, FX-heavy speed rock to gentler, mellower charms. Inevitably, debuting this material tonight leads to a distinctly uneven set.

Joint vocalists Peter Hayes (guitar) and Robert Turner (bass) still look like indie warriors. Skinny and gazing intently at the ground, they diligently thrash through feral adrenaline rushes including Whatever Happened to My Rock'n'Roll (Punk Song). It's thrilling, but hardly original.

The pace drops severely for the new material, a grab-bag of alt.blues and folksy reveries. Shuffle Your Feet is woozy narcotic gospel music that sees Hayes morphing from punk kid to raddled Delta bluesman, while Howl is opium-drone rock reduced to a funereal plod.

It's clear that BRMC are keen to lose their cartoon-rock strictures but this genre-hopping is baffling. The muted pop-blues of Promise finds a self-conscious Hayes wrestling with a trombone, while the rambling Still Suspicion Holds You Tight may have Bob Dylan consulting copyright lawyers.

Relieved cheers greet the Stooges thrash of Spread Your Love, then the closing Devil's Waitin' finds Hayes strumming acoustic Appalachian blues like a stars-in-their-eyes Leadbelly. BRMC's journey across fresh musical terrain is laudable, but you suspect their crustier fans may well be staying behind.

· At the Reading festival on Friday. Box office: 0870 380 0017.