Since the end of the AMA Supercross Championship, which was taken for the second consecutive year by Monster Energy Kawasaki’s Ryan Villopoto, the 450-class teams have been prepping their machines for the outdoor Motocross series.But the series will be lacking the reigning MX champion Villopoto, who is out injured due to tearing up his knee during a wreck at Seattle Supercross. Also out will be another top contender, Two-Two Motorsports Honda rider Chad Reed.With these two riders out, the major rivalry will be between Red Bull KTM’s Ryan Dungey, and newly-signed Yoshimura Suzuki rider James Stewart.For 2012, the outdoor MX summer series will once again feature 12 rounds with 24 motos, beginning at Hangtown this Saturday, May 19, and ending at Lake Elsinore in California Sept. 8.Following is a breakdown of each team in the 450 class courtesy of MX Sports:Monster Energy KawasakiWith Villopoto on the sidelines, former World Motocross MX2 Champion, Tyla Rattray, will make the move into the 450 Class after three seasons in the 250 Class. Rattray is no stranger to winning in Lucas Oil Motocross and will look to take advantage of his valuable experience to become an instant challenger in the premier class.“I’m really excited about the opportunity to ride for Monster Energy Kawasaki in the 450 Class,” said Rattray. “I wanted to ride the KX450F outdoors and feel really comfortable on it already.”Jake Weimer’s first season in the 450 Class in 2011 is sure to pay big dividends in his sophomore campaign. Unlike last season when he entered the championship coming off an injury, Weimer is at full-strength this summer and is prepared to take his shot at the title.“I’m looking forward to Hangtown,” said Weimer. “I finished the Supercross season strong and look forward to being on the podium (at the Nationals) as well. The goal is to be there every weekend and battle up front.”Red Bull KTMThis season, the Austrian-based KTM team signed 2010 Champion Ryan Dungey. The relationship has proven to be a fruitful one so far, with Dungey grabbing four victories in the AMA Supercross Championship. KTM’s success at the Nationals has been limited, having never won an overall, but Dungey has the tools to bring the brand into the forefront of the premier class and add to the history he’s already made for the team this season.“I’m looking forward to getting the (motocross) season started,” said Dungey. “I’m in a good place on the new KTM, and the team and I have laid down a lot of laps in recent weeks testing. It’s great to be back working with Roger (DeCoster) again. I have total confidence in the team he has assembled and the new KTM 450SX-F as we prepare for the season opener this weekend at Hangtown.”Team Yoshimura SuzukiJames Stewart’s move to Suzuki has been the biggest news coming into the 2012 season, and will likely remain the most prominent storyline throughout the season. Stewart has not raced full time in Lucas Oil Motocross since his championship-winning season in 2008, when he joined Ricky Carmichael as the only other rider in history to amass a perfect season, winning all 24 motos. What the effect of Stewart’s time away from the series will have on his speed and stamina remains to be seen, but with such impressive accolades, he is widely considered to be a title threat.“I’m really looking forward to joining the team,” said Stewart. “I’m very excited. I love the bike. Ever since I rode it from day one, I knew it was a great opportunity for me to come out and showcase my talent.”Brett Metcalfe will compete alongside Stewart at the Suzuki rig. Following a breakthrough motocross season one year ago in which he was able to grab his first career victory on U.S. soil, Metcalfe is poised to be one of the biggest threats to Dungey and Stewart. While he experienced some ups and downs during the AMA Supercross season, Metcalfe is eagerly awaiting the opportunity to race the Nationals and potentially even learn from his successful new teammate.Team Honda Muscle MilkAmerican Honda’s efforts in the 450 Class this season will be anchored by Justin Brayton, who has already established a breakthrough season thanks to a strong effort in the AMA Supercross Championship. With Trey Canard out for the year with an injury, Brayton has stepped up and now enters Lucas Oil Motocross with a lot of momentum. Brayton is a former moto winner in the 450 Class, and will look to grab that elusive first career win this summer.Tommy Hahn will step in as a substitute for the 2012 season. Like Brayton, Hahn has tasted victory in the 450 Class, coincidentally taking the overall win at the very same race that Brayton won his lone moto, back at Steel City during the 2009 championship. Hahn has been recovering from a broken leg for most of 2012, but he’s ready to get back out on the track and take advantage of the opportunity before him.Toyota/Yamaha/JGRMXDavi Millsaps is coming off the best AMA Supercross season of his career, finishing second in the championship, and now he enters Lucas Oil Motocross with considerable momentum and confidence. The Joe Gibbs Racing team hasn’t seen the success it had hoped for in 2012, but Millsaps has proven to be a bright spot. JGRMX is entering its fifth season at the Nationals and Millsaps will look to add to the team’s one overall victory over that span.Joe Gibbs Racing announced just prior to the season that Kyle Regal will campaign the summer as its second rider. Regal has proven to be an impressive motocross rider over the past few seasons, with overall podium finishes to his credit. Now, with the best opportunity of his young career ahead of him, Regal will look to build on that success.MotoConcepts SuzukiMike Alessi has been one of Lucas Oil Motocross’ most consistent threats since his runner-up finish in the 2007 premier class championship. This year, Alessi enters the Nationals aboard the same bike on which he achieved some of his greatest success – a Suzuki. Alessi will campaign the summer for the well-respected MotoConcepts team and while he may not be riding a factory bike, he is sure to be a regular at the front of the field.Team Chaparral HondaAfter a year away from the brand he has identified with for most of his 450 Class career, veteran rider Andrew Short is back aboard a Honda for the 2012 season. Short is the lone rider for the new L&Mc Racing team run by a couple of the sport’s most prominent figures – Larry Brooks and Jeremy McGrath. Short has already given the team a taste of victory in 2012, grabbing his first career AMA Supercross victory just about a month ago. As arguably the most consistent rider in the premier class over the past five seasons, Short will be looking to give his team even more success this summer.Jeff Ward Racing KawasakiFormer champion Jeff Ward has also ventured down the path of team ownership this season. Experienced riders Josh Grant and Kyle Chisholm will lead the way for the up-and-coming team, and both riders look to be challengers in the 450 Class this season. Grant is a former overall winner in the premier class and has also had some strong rides aboard his JWR machine during the AMA Supercross season. As for Chisholm, he has been a fixture in the top 10 in the 450 Class for the past few seasons and will be looking to take a step forward this summer.