RAPID CITY - More than 300 motocross riders are to twist the handgrip throttle during Saturday night's second installment of the 2007 Black Hills Arena Racing Winter Series in the warm confines of the Pennington County Events Center Arena at the Central States Fairgrounds.

The first round of the seven-event series on Oct. 6 drew 395 riders from several surrounding states.

"We get a lot of riders from around the the region, because there's just not a lot of places to race in the winter time," said Penny Ladner of Spearfish, who along with her husband Mike, a longtime motocross champion, started the indoor series four years ago.

Last month's entry numbers were actually down a bit because of other outdoor events still going on, Ladner said. About 300 riders have already pre-registered for Saturday's race, she said.

Competition classes are set up based on motorcycle engine displacement and rider experience.

Mike Ladner builds a different course on the events center clay for each event.

Heat races start at 11 a.m. to determine starting spots in the main events, which start at 6:30 p.m. Main event line-up is limited to 12 riders.

Doors open for the main events at 5:30 p.m.

The remainder of the series is set for Dec. 8, Jan. 12, Feb. 9, March 15 and April 12.