Comment 2645

By Ted Mitchell (registered) | Posted December 15, 2006 at 11:31:57

As far as preventing accidents goes, my surgeon colleagues have a rather crude saying: you can't make chicken salad out of chicken shit.

Avoiding a crash: Putting antilock brakes and stability control on a high center of gravity, non-independent rear suspension, high torsional frame deflection (unpredictable energy storage) vehicle is indeed trying to rewrite Newton's laws, or making chicken salad out of...

Trucks have a much higher single vehicle crash rate than cars, the last stat I saw was about 50% higher. How's that for crash avoidance?

Crash mitigation: Truck engineers have to do something to justify showing up for work; and indeed there have been gains over the decades in making truck frames less longitudinally stiff to reduce the damage inflicted on other vehicles. But, NHTSA's data will show that weight differentials alone do not explain the grossly asymmetric crash damage; geometry and longitudinal stiffness are still major factors. This is indefensible engineering practice - there is no necessity for either tall/square geometry or high longitudinal stiffness to meet the criteria trucks are built for.

With unibody design it is possible to have a very strong passenger compartment and sacrificial crumple zones front and back. Body on frame design cannot accomplish this goal as thoroughly without excessively weakening the entire structure.

For trucks, the sacrifical crumple zone is primarily the other car and it's occupants.

To see just how serious truck manufacturers are about safety, browse a new truck lot. These beasts are about 6 inches taller than what was considered normal a decade ago. (look at pdf photos page 7 and 8 here: http://www-nrd.nhtsa.dot.gov/pdf/nrd-50/...

Other than appearing tough and therefore selling better, the consequences of tall stance are overwhelmingly negative: harder to get in/out, easier to roll over, harder to load/unload cargo (which mostly doesn't matter to suburban cowboy buyers anyway, since the bed is typically always covered in shiny, metallic, oh-so-utilitarian fiberglass), more unstable on the road (Newton isn't going away anytime soon), and greater risk of overriding other car frames in crashes- especially the T-bone alignment. There isn't even a benefit in ground clearance, as the rear differential is the limiting dimension.

Height is a cosmetic feature with a mortality penalty. Pretty harsh.

Mr. Low is correct about other manufacturers, most Japanese companies offer body on frame design; they can't resist the high profit margin. Even Mercedes built their first iteration M series SUV on a truck frame. Competitor BMW's unibody X5 overwhelmed it in handing.

He didn't mention Honda. With the Ridgeway, a company with zero previous experience in trucks suddenly has the best handling truck on the market on their first try. It is unique in having unibody design.

These are not coincidences.

The engineering arguments and equations behind my statements will take more time to explain clearly, so look for my next article.

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