# iihs crash test results, are they apples to apples? **URL:** \ **Category:** Factual Questions\ **Created:** [July 5, 2013, 2:49pm UTC](https://boards.straightdope.com/t/iihs-crash-test-results-are-they-apples-to-apples/662721 "2013-07-05T14:49:01Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![jmwatts](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jmwatts/32/17348_2.png) [@jmwatts](https://boards.straightdope.com/u/jmwatts)\ **Post date:** [July 5, 2013, 2:49pm UTC](https://boards.straightdope.com/t/iihs-crash-test-results-are-they-apples-to-apples/662721/1 "2013-07-05T14:49:01Z")
I’m looking over crash test results at [http://www.iihs.org/ratings/default.aspx](http://www.iihs.org/ratings/default.aspx). If you click on the various vehicle types, you’ll see their top safety picks, including the “top safety pick+” (TSP+). So obviously it’s easy to pick the safest vehicles per category. However, I’m wondering if a TSP+ car in the small car category is equivalent to a TSP+ large SUV? Are the tests performed in the same manner, regardless of vehicle? I’m wondering if the test for a small car is different than a test for a 5000lb SUV, therefore the safety ratings aren’t really equivalent among different categories. ---
**Author:** ![GreasyJack](https://avatars.discourse-cdn.com/v4/letter/g/df705f/32.png) [@GreasyJack](https://boards.straightdope.com/u/GreasyJack)\ **Post date:** [July 5, 2013, 4:26pm UTC](https://boards.straightdope.com/t/iihs-crash-test-results-are-they-apples-to-apples/662721/2 "2013-07-05T16:26:53Z")
They aren’t comparable. The main head on collision tests that make up much of the safety rating are designed to simulate a collision with a car of the same weight, so they’re only comparable among similar sized cars. I believe the side impact and low speed crash tests are all done the same with all cars, though. [http://www.iihs.org/ratings/frontal\_test\_info.html](http://www.iihs.org/ratings/frontal_test_info.html) ---
**Author:** ![jmwatts](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jmwatts/32/17348_2.png) [@jmwatts](https://boards.straightdope.com/u/jmwatts)\ **Post date:** [July 6, 2013, 3:46am UTC](https://boards.straightdope.com/t/iihs-crash-test-results-are-they-apples-to-apples/662721/3 "2013-07-06T03:46:33Z")
> [@GreasyJack](#): > > They aren’t comparable. The main head on collision tests that make up much of the safety rating are designed to simulate a collision with a car of the same weight, so they’re only comparable among similar sized cars. I believe the side impact and low speed crash tests are all done the same with all cars, though. > > [http://www.iihs.org/ratings/frontal\_test\_info.html](http://www.iihs.org/ratings/frontal_test_info.html) Ah, thanks **GreasyJack** , that certainly puts a spin on things. From the page you referenced: > [@](#): > > Frontal crash test results can’t be used to compare vehicle performance across weight classes. That’s because the kinetic energy involved in the moderate overlap and small overlap frontal tests depends on the speed and weight of the test vehicle. Thus, the crash is more severe for heavier vehicles. > [@](#): > > Given equivalent frontal ratings, the heavier of two vehicles usually offers better protection in real-world crashes. I can’t make sense of this. That page basically says that they’re running cars into barriers, so I’m not sure how they would be simulating collisions with cars of the same weight. Also, above it says “the crash is more severe for heavier vehicles” but then that the heavier vehicle usually offers better protection. Not sure I’m any farther along than when I started, besides having the idea that being in a Suburban is better than being in a Civic, and that the crash ratings really only compare cars in that same weight class. ---
**Author:** ![Pinmin](https://avatars.discourse-cdn.com/v4/letter/p/4af34b/32.png) [@Pinmin](https://boards.straightdope.com/u/Pinmin)\ **Post date:** [July 6, 2013, 3:55pm UTC](https://boards.straightdope.com/t/iihs-crash-test-results-are-they-apples-to-apples/662721/4 "2013-07-06T15:55:08Z")
> [@jmwatts](#): > > I can’t make sense of this. That page basically says that they’re running cars into barriers, so I’m not sure how they would be simulating collisions with cars of the same weight. Also, above it says “the crash is more severe for heavier vehicles” but then that the heavier vehicle usually offers better protection. Not sure I’m any farther along than when I started, besides having the idea that being in a Suburban is better than being in a Civic, and that the crash ratings really only compare cars in that same weight class. Physics. Two identical cars crashing head on is almost identical to one car crashing into a solid barrier. But think about a Suburban and Civic hitting head on. They basically share the crash energy evenly, but the size difference means the Civic is absorbing more energy than it contributed and the Suburban less. ---
**Author:** ![Throatwarbler\_Mangrove](https://avatars.discourse-cdn.com/v4/letter/t/8c91f0/32.png) [@Throatwarbler\_Mangrove](https://boards.straightdope.com/u/Throatwarbler_Mangrove)\ **Post date:** [July 7, 2013, 4:13am UTC](https://boards.straightdope.com/t/iihs-crash-test-results-are-they-apples-to-apples/662721/5 "2013-07-07T04:13:05Z")
> [@jmwatts](#): > > Ah, thanks **GreasyJack** , that certainly puts a spin on things. From the page you referenced: > > I can’t make sense of this. That page basically says that they’re running cars into barriers, so I’m not sure how they would be simulating collisions with cars of the same weight. Also, above it says “the crash is more severe for heavier vehicles” but then that the heavier vehicle usually offers better protection. Not sure I’m any farther along than when I started, besides having the idea that being in a Suburban is better than being in a Civic, and that the crash ratings really only compare cars in that same weight class. The crash is more severe for heavier vehicles because a heavier vehicle moving at the same speed is going to have more energy for the crash structures to dissipate. On a head-on collision between a suburban and a civic, the suburban _may_ come off better supposing it has the same well designed energy absorbing structures, which it may not. The Suburban is a body-on-frame vehicle, and BOF is a way of building vehicles that generally isn’t used much today for passenger cars. The body itself may not be very sturdy or designed to deal with impacts, since it doesn’t actually bear any of the load of the vehicle. Against a solid object like a tree it would not fare well, and in a rollover accident it would definitely not fare well, since the body of a BOF vehicle usually doesn’t have very strong pillars to hold up the roof, _and_ in the event of a rollover the heavy ladder frame at the bottom of the vehicle will impart additional weight and force on the body. I leave to you to find out what the likelihoods are of being involved in each type of fatal crash.