Weight of a Car as a factor in determining car safety

http://www.safecarguide.com/exp/safety/idx.htm

pl see the above thread, it says generally larger heavier cars are safer and a large car with poor rating will easily produce better result that a lighter car with good ratings,

what's your opinion friends on this?

Santhanam

We were comparing small cars with larger cars (like Etios Liva Vs Linea). If we are talking about trucks, pickups (even the SUVs which are refered to could be huge and is generally referred to as trucks in US), then things will change.

If we draw two graphs, one showing the advantage by increase in size and other by advantage by safety features, at some point the size advantage will overtake the other. For example if a Wagaon R with all the saftey features have a high speed head on collision with a 20 tonne trailer, we all know what will be the end result.

Tomy

Dear All, 

Just wanted to add my humble 2 cents here. A heavier car would require more braking power as the mass is more. Also, weight transfers when a car takes a turn or applies brake hence EBD was invented.

Weight cannot alone be considered as a safety parameter. Its more to do with the crumple zones, head restraints, shock absorbing body etc etc.

If 8 lacs is the budget and safety is of prime importance, I recommend the Fabia or the Rapid because :

1. Build quality on german standards (Laser welding)

2. Spacious (the fabia and the Rapid are lengthier than most of its counterparts)

3. Safety Features (the Rapid has ABS and Airbags in the Ambition variant)

The Fiat Punto Emotion Pack is also a good option. It has Euro NCAP Ratings of 5 stars. But you will have to compromise on the rear legroom.

Again, one more point which I mentioned earlier also.

When you are comparing two cars on safety, dont assume the "duel" between the cars alone - i.e. dont assume that all accidents are caused by direct collision between the two cars which are being compared. This is one of the possibility with a low probability. Why are we not considering all possibilities of accidents where each car can independently get involved.

For example, here is a light car with ABS. Suppose brakes were applied quickly on a wet & slippery mountain road. It stops with perfect control. And there is a heavy car without ABS which also applies brakes but the wheel locks and it slips and goes out of control and falls into the valley. Now where does the comparison stand in this case? If we compare only on certain scenarios, the outcome will be skewed.

Tomy

"Why are we not considering all possibilities of accidents where each car can independently get involved."

Ok, we shall start on case by case basis:

There can be a number of cases. Esteemed members are requested to add more cases as they can think of.

Case 1. Say a slow moving truck (20 kmph) collides with a.) Light car  b.) Heavier car c.) A SUV (say safari). Collision can be head on OR side hit (Perpendicular OR any angle). Which vehicle will ensure more safety?

Case 2. Same case as above with fast truck (say on an expressway) 

Case 3. Wet surface skidding.

N.B. Lighter cars considered with safety and heavier vehicles without safety features.

if a large heavier car with poor rating will easily outperform a smaller, lighter car with good rating (as described in the above website) i've this question,

Hyundai Accent (Euro NCAP rating 1/5=poor) collides with Hyundai i10 (Euro NCAP 4/5=good), will the passengers inside Accent be safer than those inside i10, 

in that case isn't it better to opt for Accent Executive than i10 Asta with 2 airbags. (both comes in same price range)

this question was worrying me for long, can any friends enlighten us on this.

Santhanam

One more general comment on this topic is that, the possibilites of accidents are so complex that we cannot conclude anything by looking at some parameters. In some specific types of accidents, weight of the car helps. In some other type accidents, the safety features will be more useful. If the weight difference is less, the safety features will have an upper hand. But if we are talking about a really huge car, then size will have its own benefits (again, for some types of accidents only).

I remember one accident whcih happened to my cousin last month. It was a Maruti 800 going at around 80Kmph. Obviously, it has no saftey features like ABS, Airbags etc (other than seat belt) and is one of the lightest cars. It was night and he dozed off for a moment and the car lost control and hit something (stone or something). Hearing the sound he woke up, by that time the car had gone into a cartwheel movement. He gripped the steering wheel tightly and counted 7 revolutions of the car, some in the air, some on the ground. The car was crushed like a paper ball. And what is most amazing? He came out without a single scratch!!! The police officers who were behind him came to his rescue and were shocked to see the state of the car and amazed to see that he was alive. They offered him to be taken to hospital but he opted to go home and they dropped him home. Of course, he did a CT scan next morning, but not injury at all.

I think in this case the cartwheeling of the car absorbed the linear momentum and converted it into rotational motion, and came to a slow halt, avoiding severe shocks inside the car.

There could be exactly reverse case also.Less damage to car and more injury to passengers.

So it is difficult to "plan" the outome of an accident. Luck plays a role (though highly technical people don't like the word "luck").

Tomy

I completely agree with Tomy. Even an Omni of a known relative rolled twice after being hit from behind by a truck. The driver did not even have a single scratch, but the car was partially crushed, with a totally non existent rear portion(boot area). Didnt the "cheap bread box on wheels" save its driver? I agree that the car has no protection to frontal collisions, but thats another case. 

So, the type of damage to car and occupants depends upon the type of collision that takes place. An i10 collides with an accent in the front. The engine bay of the i10 will be deformed, but I doubt that the occupants will be affected much as damage done is done to the car and force is absorbed there. Imagine the reverse. If the accent fails NCAP for frontal collisions owing to its strong structure, the occupants will be thrown to the front due to rapid decelaration. 

This will lead to the drivers head crashing into the glass, which is fatal enough, and same forr the front passsenger. Not sure about the rear though. Also, please do note that even if the driver and passenger wear seatbelts, rapid decelaration can even make the seatbelts deadly. Only a combination of active, passive safety features, a crash-absorbing structure, last but not the least a sensible driver and a well disciplined traffic can make a car safe!

Actually we can compare cars of similar siz when both have same safety features.

In this case, we can compare Toyota Etios with Tata Manza with airbags and ABS. Etios has weight 900 kg and Manza is 1200.

If we consider both cars in same type of colision with same speed, then I guess manza could be safer.

More weight can be benefit over lighter car in same type of on road collision or similar when force is not too big. But in other case like falling in valley may not help to any type of car or SUV.

In India, lighter cars means cost cutting and less metal. Etios has lots of cost cutting and lesser metal. I dont know if Etios has been crash tested.

Although our modertor has mentioned one accident of Omni and driver coming out safe, you cant bet Omni is safe vehicle. It is also depends on probability that omni rolled and did not get crushed. Omni should be considered unsafe car, or many say, Card Board / match box.

It is difficult to clearly state or determine who the winner is - that is why there are crash tests. That said between two cars colliding with each other, simple physics (conservation of momentum) states that, v1/v2 = k.M2/M1, where M1 and M2 are the mass of each car and v1 & v2 are their velocities respectively after collision. k is a constant of proportionality. Now, if M1 = M2, both cars will have the same velocity after collision (and it will be the same as that before collision). If M1 > M2, then M1 will have less velocity after collision while M2 will have greater velocity after collision - simplistically assuming that greater velocity after collision implies greater damage, M2 (i.e., the lighter car) will have greater damage. If this means greater damage to the passengers is a matter of probability.

Of course, this simplistic analysis is just that: Simplistic. Real life has many more variables and parameters as evident in the above posts...