July 30 (Reuters) - Rivian Automotive ( RIVN ) beat quarterly revenue estimates and raised annual delivery forecast on Thursday, buoyed by optimism over the rollout of its lower-priced R2 SUV and growth in its software business as it expands beyond its premium lineup.

The results suggest that the electric-vehicle maker's long-awaited push into the mass market has picked up pace. It began customer deliveries of the Tesla Model Y rival during the second quarter and improved its outlook for deliveries, adjusted core profit and capital spending despite a softer U.S. EV market.

Rivian said it hosted a record number of R2 demo drives during the quarter, reflecting strong customer interest in the vehicle.

"We've been very positively encouraged by the conversion rate of reservations to orders for the Launch Edition. It is meaningfully above our own internal projections," CEO RJ Scaringe told Reuters.

The company will start to see positive gross margin on the R2 vehicle in the back half of the year, he said.

Rivian's expansion into the lower-priced segment comes as U.S. EV demand has slowed following the expiry of a federal consumer tax credit in September last year.

Revenue rose 27% to $1.66 billion, topping analysts' average estimate of about $1.51 billion, according to data compiled by LSEG.

The company delivered 12,194 vehicles during the April-June quarter, up from 10,661 a year earlier, while production increased to 12,613 vehicles at its Normal, Illinois facility.

Rivian raised full-year delivery forecast to 65,000-70,000 vehicles from 62,000-67,000. It lowered planned capital spending projection to between $1.7 billion and $1.8 billion, from $1.95 billion to $2.05 billion earlier, and expects a smaller adjusted core loss.

Software and services revenue climbed 37% to $515 million, with $308 million coming from Rivian's joint venture with Volkswagen, showcasing the growing importance of software alongside vehicle sales.

The EV maker is increasingly relying on software and technology licensing to diversify revenue beyond vehicle sales.