Small car=Deathtrap? Your opinion?

[hamsterpower]

Originally Posted by Frank Lee

I know a semi-driver who was hit by another semi and will be a vegetable for the rest of his life. So much for the large vehicle arms race, when you get screwed even at the very top.

I have seen the same thing. I saw the aftermath of a empty semi tanker that hit a small box truck from behind on the highway. The box was severely damaged but the cab was fine. The tanker was a different story. The cab parted ways with the frame and was nearly unrecognisable. I don't believe semi driver survived.

In 5 plus years as a traffic spotter, I see roll-overs every day. Three of them have been small cars.

[PaleMelanesian]

That video showed me there are good and bad small cars. The Yaris got smashed, but that's an older model car. The new model Fit held up amazingly well against the Accord. The Smart... held its structure but got thrown so far as to almost guarantee a secondary impact.

The obvious answer they're trying to tell us is, buy the Camry or Accord. My conclusion is different: buy the Fit. You get the advantages of a small car and reasonable safety.

[serialk11r]

Originally Posted by IamIan

You have it backwards.

F=MA
or
Kinetic Energy = 1/2MV^2

Under the same deceleration ( say you hit a stationary object ) or the same initial speed ... the more mass you have the more impact energy you have. Mass increases the impact energy not decreases it... Mass doesn't absorb the impact energy , it increases it.

A better design is a better design ... that part I'll give you ... but the mass part you have backwards.

I said energy absorbed INTO the structure, rather than transferred kinetic energy.

Originally Posted by jamesqf

Unfortunately, the data doesn't support your thinking. See the Wenzel & Ross paper, and particularly the differences between body-on-frame SUVs and unibody designs.

Hmmm I guess. I also forgot that SUVs tend to be a lot higher and so the strength of the doors is less relevant since you'd be getting hit closer to the frame. My bad.

[IamIan]

Originally Posted by serialk11r

I said energy absorbed INTO the structure, rather than transferred kinetic energy.

Impact energy is the transfer of Kinetic energy ... they are not separate or different things.

You credited a larger mass itself for absorbing more impact energy:

Originally Posted by serialk11r

A heavier car absorbs more impact energy into the structure

Which is still incorrect.

It is the design of the structure that would allow it to absorb or not absorb the energy of the impact.

More mass itself ... will ALWAYS increases the energy of the impact ... mass itself does not absorb impact energy it adds more impact energy to the event.

Two vehicles of identical design expect Car A weighs more than Car B ... both vehicles experience the same collision event with a stationary object at the same speed ... Car A with it's greater mass will have more impact energy than car B ... This is just the way the world works ... KE=1/2MV^2 and F=MA ... A heavier , more mass itself always equals more energy and more force... what you wrote about heavier absorbing more impact energy ... is backwards.

A good design can sometimes compensate for the mass penalties ... but that design benefit does not change the penalties of the greater mass ... the design benefits try to overcome or compete with the penalties of greater mass.

[sheepdog 44]

I'm thinking of the future in mind when i say this. If everybody drove really light cars under 1500 lbs as i think we will have to do in the future, then i suppose it would be safer overall. I would think that two 1500 lbs cars colliding head on would experience less G's in deceleration as the crumple zones don't also have to absorb an extra 2000 lbs or more mass. A future low mass vehicle would be designed to hold structural integrity and not implode. A low mass vehicle also doesn't necessarily have to be small, It can take up the space of a larger car giving it a larger crumple zone. More of the mass could be designed into safety features instead of just relying on the "dead weight" of 1000 more lbs to save you.

As far as hitting a legitimate source of weight on the highway such as a commercial truck or tractor trailer, weight will not save you up to a point. A lighter car would be more manueverable and brake faster avoiding head on collisions easier which would be much safer overall. Less accidents, safer low impact accidents, safer pedestrian accidents. Overall just much safer across the board compared to the marginal improvement of safety a higher mass vehicle offers in certain situations, and then that is only for you.

The best thing you can do is just buy a car with a good crash rating. A compact car today is much safer than a compact of the same size and weight from the 80's. It's not the weight, it's crashworthiness designed into it

The biggest problem i see with those mini city cars in the video is that they just dont have enough of a crumple zone in the front! That is a design liability, and i do disagree with them being that short. You can have the same mass and add 3-4 feet to that car in length and it would be much much safer. Furthermore your mpg would get much higher. More length doesn't add to the area of drag and it'll improve aerodynamics so much like the Aero civic. Ecomodding Boat tails and bullet nose extension are good for gas and safety! Get with the picture car manufacturers!

[jamesqf]

Originally Posted by PaleMelanesian

The obvious answer they're trying to tell us is, buy the Camry or Accord. My conclusion is different: buy the Fit. You get the advantages of a small car and reasonable safety.

But as we keep trying to tell you, you're still stuck in the attitude that the only thing that matters for safety is what happens when your car gets hit by another car, when the point is to avoid being hit (or hitting something, rolling over, etc) in the first place.

[gascort]

Originally Posted by IamIan

#1> Someone is always bigger/heavier than you.

#2> The bigger / heavier vehicle is more dangerous to everyone else around

#3> There are other types of accidents than head on car vs car.
Any accident involving hitting a stationary object the heavier car is less safe than the lighter car. It brings more energy into the collision. The human body has the same injury from force tolerances no matter the vehicle. This forces the heavier vehicle to be less safe than the light vehicle....

#4> The heavier vehicle is more likely to get in an accident in the first place.
It's inertia ... the heavier vehicle's greater inertia reducing it's ability to brake to a stop or turn a tight corner to get out of the way...

I agree with you on #1 and 2.
Your #3 argument seems to make sense until it contradicts itself. More energy in the car or in the passenger? Energy in the car relates back to #2; it doesn't relate to the passengers. Energy in the passengers is primarily managed in a collision. Unless you are talking about a side impact with a disproportionately massive but weak car or a truck carrying a trailer which will move forward and crush the driver.
I disagree with your #4. Greater inertia yes, more difficult to accelerate yes. What about proportionately more frictional force between the ground and tires? This cancels out any effect of greater inertia in the end. You can double a car's mass and expect it to stop in the same distance if all else is held constant (especially center of gravity).

A LARGER car is more safe in all accidents, especially one that's designed to crumple and absorb energy over a greater distance. Mass is only relevant in the "my car is bigger" argument, which yes, there is always someone bigger.

[gascort]

Originally Posted by IamIan

Two vehicles of identical design expect Car A weighs more than Car B ... both vehicles experience the same collision event with a stationary object at the same speed ... Car A with it's greater mass will have more impact energy than car B ... This is just the way the world works ... KE=1/2MV^2 and F=MA ... A heavier , more mass itself always equals more energy and more force... .

This force you cite here would be important for the tree, brick wall, etc. getting hit, not the driver.
More force acting ***on what object?*** is the specific way to apply this. The increased force acting to stop the more massive car acts *on the car*, and it has more mass, giving it a proportionally equal value of acceleration.
What is experienced by the person inside is relative to the quantity of acceleration they experience inside the car that is having this force imparted to it. Assuming both cars crush say, 0.50m, at the same rate, both drivers experience the exact same force during impact with said stationary object.

*Now if one driver is fatter than the other, HE has more impact energy to be dissipated, and HE will experience a proportionately greater force *acting on him*.

That said I voted for the compact and just drive safely. You can avoid accidents by being observant and alert, and not driving faster than necessary (as you mentioned, velocity is critical in Kinetic Energy)
Most wrecks are due to driver error or inattention so you can save a lot by being careful yourself and watching out for others.

[niky]

Originally Posted by gascort

I disagree with your #4. Greater inertia yes, more difficult to accelerate yes. What about proportionately more frictional force between the ground and tires? This cancels out any effect of greater inertia in the end. You can double a car's mass and expect it to stop in the same distance if all else is held constant (especially center of gravity).

While I agree about absolute braking distances, having driven some big cars that can hang you off the seatbelts under full braking, I have to say: If you double a car's mass, it's not very easy to keep everything else constant.

You can make a very heavy car turn and stop very well, but as Nissan has shown with their R35 GT-R, it takes some really good brake balancing, some really gooey rubber and a really, really stiff suspension to do it. And even then, once the tires give out and physics take ahold of the car, say sayonara... there are some pretty entertaining videos of GT-R drivers running out of talent (or brains) and sliding the car straight into the outside railing.

There was an accident here about two years ago. Local TV celebrity understeered his GT-R off a cliff and killed his publicist, who was sitting in the back seat. Was quite familiar with that road, as I'd driven it just as hard myself a number of times. Wouldn't go so far as to say he wouldn't have gotten into that accident with a lighter car, but I often wonder if he'd have smashed up as hard in something like an EVO, or maybe an Aveo... but given the horrid frontal crash structure of the Aveo,...

-

I prefer cars small. Compacts nowadays are bang on the safety ratings of midsized cars, with a smaller fuel economy penalty. Of course, they're starting to get piggishly heavy, but there are those who try to stay closer to the compact norm (Civic, Corolla, Elantra) and are pretty light.

I can swing subcompacts, and I've even driven superminis like the Spark and Hyundai i10 on the highway between semis without fear. At least, not with anymore fear than I would have in the family CR-V.

Except for the fact that tiny cars almost invariably have horrible brakes.

[PaleMelanesian]

Originally Posted by PaleMelanesian

The obvious answer they're trying to tell us is, buy the Camry or Accord. My conclusion is different: buy the Fit. You get the advantages of a small car and reasonable safety.

Originally Posted by jamesqf

But as we keep trying to tell you, you're still stuck in the attitude that the only thing that matters for safety is what happens when your car gets hit by another car, when the point is to avoid being hit (or hitting something, rolling over, etc) in the first place.

I don't see that in my statement at all.

Talking about crash avoidance, my answer is still the same. From the list of Camry, Accord, Fit, Yaris and Smart, which will maneuver and get you out of trouble the best? Fit.