Who has the strongest roof? Do all crossovers have the same roof strength to protect occupants in a case of a rollover? Insurance Institute for Highway Safety (IIHS) performs a series of crash tests and safety evaluations. One of the tests they perform is the “Roof strength” test. This procedure is fairly straight forward and its results can be displayed in an easily understood graph. (See IIHS video below, which demonstrates the test).
The strength of the roof is determined by pushing a metal plate against the driver’s side of the roof at a slow and constant speed. The force applied relative to the vehicle’s weight is shown as the strength-to-weight ratio. The graph shows how the ratio varies as the metal plates continues to push against the vehicle. The peak strength-to-weight ratio recorded at any time before the roof is crushed five inches is the key measurement of roof strength.
“Good” rating requires a strength-to-weight ratio of at least 4.oo. In other words, the roof must withstand a force of at least four times the vehicle’s weight before the plate crushes the roof by five inches. The higher the number – the better. And the steeper the graph in the beginning – the stronger the roof structure and the lesser distance the roof is likely to squish during an accident.
This table shows how 2013 and some 2014 compact crossovers faired with this test. The Volkswagen Tiguan has the highest Force Ratio. It can withstand a force of 5.82 times its own curb weight. If you look at F-150’s graph carefully, you can see that as the force is continued to be applied past 3.4 inches – the roof becomes a little weaker. This graph shape is typical for most vehicles. The structural rigidity of the roof can only go so far.
|Force Ratio||Roof Deflection||IIHS Rating|
|2013 VW Tiguan||5.82||N/A||Good|
|2014 Mazda CX-5||5.47||3.34 in||Good|
|2013 Honda CR-V||5.08||2.85 in||Good|
|2013 Ford Escape||5.03||2.43 in||Good|
|2013 Toyota RAV4||5.00||4.04 in||Good|
|2014 Subaru Forester||4.95||3.52 in||Good|
|2013 KIA Sportage||4.43||3.77 in||Good|
|2013 Jeep Patriot||4.25||N/A||Good|
|2013 GMC Terrain||4.17||3.34 in||Good|
|2013 Chevrolet Equinox||4.17||3.34 in||Good|
|2013 Nissan Rogue||3.34||N/A||Acceptable|
See image gallery below for each individual graph.
This video from IIHS.org shows what happens to a 2009 VW Tiguan and a 2008 KIA Sportage when equal crush force of 15,000 pounds is applied to each: