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By Phil LeBeau, CNBC

New crash tests show bigger is not always better when it comes to the safety of midsize SUV's.

The Insurance Institute for Highway Safety put seven midsize sport utility vehicles through small overlap crash tests and rated four as either poor or marginal.

"It is a little disappointing," said Dave Zuby Chief Research Officer for the IIHS. "You would like to see more good and acceptable performers in these small overlap crash tests."

The Jeep Cherokee, Dodge Durango, and Hyundai Santa Fe were rated as "marginal" following the crash tests.

Meanwhile, the IIHS gave the lowest rating possible, "Poor" to the Dodge Journey. By comparison, the four-door Jeep Wrangler and Nissan Murano received a rating of "good" from the IIHS. The Ford Flex had an "acceptable" performance according to the Insurance Institute.

"You would like to see more good and acceptable performers in these small overlap crash tests."

"What we are seeing for Dodge/Chrysler brands is that when they are bringing out new designs they are performing pretty well in our test," said Zuby. "These older designs that have been around for a few years aren't offering the highest level of safety in this type of crash."

The small overlap crash test replicates the impact of the right front corner of a vehicle crashing into another vehicle, tree or pole at 40 MPH.

The IIHS says a quarter of all injuries and fatalities in front collision auto accidents occur in small overlap crashes.

FCA USA, the parent company of the Jeep and Dodge brands says the latest round of crash tests do not reflect the overall safety of Jeep and Dodge midsize SUV's.

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"No single test determines overall, real-world vehicle safety. Every FCA US vehicle subjected to IIHS evaluations of four key crash scenarios — moderate-overlap, side-impact, roof-strength and head restraints/seating – received the highest possible ratings in each," said Eric Mayne, a spokesperson for FCA USA. "Every FCA US vehicle meets or exceeds all applicable federal motor-vehicle safety standards."

While theses crash tests raise questions about the safety of some Dodge and Jeep brand SUV's, it's unclear how much they will hurt sales of SUV's for both brands.

This year, Dodge sport utility sales are down less than 1 percent while Jeep brand sales are up 21.8 percent.

Last year, the Jeep brand had annual sales that topped one million vehicles for the first time ever.