Go Back   Team-BHP > Under the Hood > Technical Stuff


Reply
 
Thread Tools Search this Thread
Old 5th October 2014, 13:35   #121
BANNED
 
Join Date: Oct 2013
Location: bangalore
Posts: 522
Thanked: 459 Times
Infractions: 0/1 (7)
Default Re: Sheet Metal Thickness - Does it matter?

Maruti/Toyota/Honda/Hyundai users can now feel safe in their thin metaled cars could be as safe as thick metaled ones. It is an important takeaway from this thread as much as it is misleading. It would be good if people use these info when they shop for their cars than use it to justify their purchases. After all, most of us did not buy our cars knowing that it is safe. If what we need are structurally safe cars, we should ask our favourite manufacturers whether their cars are indeed structurally safe, than being happy that one of the parameters that was tormenting us is out of the way. One phrase (sheet metal thickness) has given way to another (structurally safe), but things largely remain just the same - Indian cars are unsafe. Our manufacturers cut costs wherever they can. While thin skinned car owners can be happy that their cars could be, not so unsafe as they believed, others could be happy that their manufacturer, who did not skimp on sheet metal, is less likely to skimp on structural safety.

As somebody said, "out of sight is out of mind". if only we had a way to see what is "inside" the car.
blacksport is offline   (4) Thanks Reply With Quote
Old 5th October 2014, 18:22   #122
BHPian
 
dark.knight's Avatar
 
Join Date: Apr 2013
Location: India
Posts: 819
Thanked: 1,877 Times
Default Re: Sheet Metal Thickness - Does it matter?

I've commented on these topics earlier but let me go a little more into the technical aspects today, I'm not an expert at all but I'm putting this together with whatever little knowledge of cars and physics I have. Also I happened to browse and read up on a website called engineersedge(dot)com on sheet metal gauge specifics. To the best of what I know the scale of gauge normally used in cars today differ from 20-16, maybe the range is more but I'm not sure it can go lower than 20. The thickness & weight (per sq.ft) of each is as follows :

Gauge | Thickness | Weight per sq.ft
20- 1.01 mm- 1.465 lbs or .66 kg
19- 1.16 mm- 1.705 lbs or .77 kg
18- 1.31 mm- 1.950 lbs or .88 kg
17- 1.46 mm- 2.195 lbs or .99 kg
16- 1.61 mm- 2.440 lbs or1.10 kg

The figures above are examples for galvanized steel, which is used in the automobile industry. Steel and stainless steel are almost the same specifications except with 1-2% lower weight in stainless steel across gauges and upto 5-6% lower weight in steel. Thicknesses too vary slightly. From the above its clear that weight too increases significantly with usage of thicker sheet metal and for a small difference of .6 mm the weight goes up by 440 grams per sq.ft of sheet metal.

I never contested that higher spec gauge would be more rigid and tougher to bend than thinner ones, however the way a car moves is dependent on the weight of the machine. In an era where governmental agencies give incentives/approvals only to the most eco-friendly cars, manufacturers can no longer make cars as heavy as they used to be. Even the customers want frugal fun-to-drive cars, however high end they maybe. Lets take a look at the latest Bimmer M4 body materials :

Name:  carbon fibre.jpg
Views: 3310
Size:  23.1 KB
Full carbon fibre reinforced plastic (CFRP) on the roof. While CFRP is bendy in nature, it is 6 times stronger than steel and yet half its weight. The strut brace & drive shaft are also made of the same material.

Name:  alfender.jpg
Views: 3212
Size:  73.2 KB
The front of the M4 is made of pure aluminium which is stronger than steel, but more malleable and lighter.

Name:  rear axle.jpg
Views: 3202
Size:  74.3 KB
Only the rear axle is made of steel whereas the front is aluminium to save weight. All these additions have made the M4 about 90 kilos lighter than the previous M3, yet its just as fast with a turbo charged V6 engine than its more thirsty E90 NA V8 cousin.

There is no doubt that as the number of cars increase on our roads, environmental concerns have made manufacturers resort to alternative materials to save weight yet retain the safety. It all depends on the structural soundness of the vehicle with strategically welded impact beams on the sides and both ends of the vehicle's frame. Strategically placed body panels made of CFRP or ABS plastic may not be as rigid or strong as a 16 gauge sheet, but they will be much lighter and equally or more resistant to dents as they are bendy and will restore shape even after a somewhat hard impact.

Therefore like I said before and in agreement with the overall conclusion of this room, sheet gauges were made thick before, but they are increasingly a thing of the past as vehicles aim to be quick to roll, dynamic, yet with a smaller engine to increase conservation of fossil fuels, be environment friendly yet fun to drive while being equally safe with the use of electronic safety assist devices like ABS, SRS, EBD, radar-braking etc.

Last edited by dark.knight : 5th October 2014 at 18:24.
dark.knight is offline   (4) Thanks Reply With Quote
Old 5th October 2014, 20:46   #123
BHPian
 
amit_purohit20's Avatar
 
Join Date: May 2006
Location: mumbai
Posts: 546
Thanked: 431 Times
Default Re: Sheet Metal Thickness - Does it matter?

Is it possible to design a SUV with body on frame construction to achieve NCAP rating of 5?

From the discussion going on it seems its not possible without a monocoque construction.

If so does it really makes sense to buy a SUV of body on frame construction and risk our lives?

Again I believe its the design of the internal structure members of passenger cabin and the crumple zones which make a vehicle safer and not the sheet metal thickness used in a door or bonnet or dickey.

Yes a higher sheetmetal thickness used in passenger cabin design would help to make it more stiff. Again here how the higher sheetmetal thickness is exploited to make the cabin more stiff is upto the design quality.

I feel its not the European Cars greater sheetmetal thickness (for doors, bonnet etc) which saves life, but its the higher weight of metal used in increasing passenger cabin stiffness.

A crumple zone is designed to crumple but it should not crumple very easily so that the whole engine comes in the passenger cabin, neither it should be so rigid that it hardly crumples and transfers all the impact energy to the passenger cabin.

Striking the right balance is essential!
amit_purohit20 is offline   Reply With Quote
Old 5th October 2014, 20:55   #124
Senior - BHPian
 
Join Date: Oct 2012
Location: Delhi
Posts: 2,567
Thanked: 4,578 Times
Default

Quote:
Originally Posted by amit_purohit20 View Post
Striking the right balance is essential!

Quite right. I would not get to much hung up about it, because I think a lot of these SUVs are not very safe to start with. We have been discussing safety more or less from a construction and design point of view once you find yourself in an actual accident. Staying out of an accident is just as important. Not all, but quite a few SUVs are notoriously poor when it comes to handling and braking.

We have a lot of friends in Suffolk, UK. And they all insist on buying SUVs as they live out of in the country. But my wife's little Ford Fiesta is probably safer with better traction on wet and snowy roads then these most of these so called SUVs.

They are like some of the esteemed members on this forum. Its heavier, bigger, you sit high up, so it mist be better and safer. Fat chance!

Jeroen
Jeroen is offline   (3) Thanks Reply With Quote
Old 5th October 2014, 22:09   #125
BANNED
 
Join Date: Nov 2011
Location: India
Posts: 582
Thanked: 455 Times
Default Re: Sheet Metal Thickness - Does it matter?

Quote:
Originally Posted by amit_purohit20 View Post
Is it possible to design a SUV with body on frame construction to achieve NCAP rating of 5?

From the discussion going on it seems its not possible without a monocoque construction.

If so does it really makes sense to buy a SUV of body on frame construction and risk our lives?
Actually problem is in identifying the purpose behind buying the vehicle.

Usually buyers consider SUVs like any other road worthy vehicles and they feel the SUV are more safer because they are heavier, have more thicker metal and 'look' rugged so end up buying them. Then they end up driving them faster on the flat roads, that turns the SUVs into dangerous vehicles.

Main issue is not the body on frame construction, rather its the weight of so much of metal which doesn't let the whole bulk stop or jump after collapse. The weight of the SUV just keeps pushing it from behind into the other vehicle or obstacle where it collapsed. Now since there is no specifically designed crumple zone ahead, the cabin (weakest part of the SUV) acts like crumple zone and gets crumbled. If speeds are within the limit then SUV will stop much earlier after the crash and damage in the cabin will be lesser. Simple law of physics.

Here we will have to understand that the SUVs are usually driven at much higher speeds than they are supposed to be. Less than 70 km/hr is very safe in any Safari, Scorpio or Fortuner but we usually see them flying at around 100 km/hr or more on highways.

First of all we will have to understand what is SUV?

Its a type of vehicle which is supposed to handle all kind of terrains and also has some capabilities to drag some other vehicle which has got stuck somewhere. Then the vehicle construction should be rugged enough so that it can tolerate quite a few beatings and abuse while driving on extreme surfaces. So obviously the outer panels have to be made of thicker sheets. The seating position is very near to front glass and positioned higher so that driver can see the bonnet and maximum possible area around the bonnet which is much needed while negotiating tight corners, slush or extreme uneven terrains.

Building a vehicle capable of all this results into a bulk of metal which can withstand in low speed crashes and bumps which are normal during offroading. And there is need of such vehicles for such tasks.

A lightweight monocoque SUV like Duster will have hard time doing all these jobs and this is where rugged and heavyweight Safari or Endeavour will come handy. Now these are not the vehicle which are supposed to be driven at high speeds on flat highways, then bang them into other vehicles by just thinking that we are seating at higher positions and carrying much higher weight of metal so its the other vehicle which is going to pay the price.

SUV will be safe if driven within it's limits.

Then there is different category called crossovers. These are for those who want little bigger vehicle than the cars and want to sit at 'little bit' higher seating position. Offroading is not the purpose here. These type of vehicles are heavier than cars but lighter than SUVs and don't have too much of height, neither too much raised from the ground. These can be driven at higher speeds than SUVs.

I see few comments here that people find higher seating position more safe! Man, the high seating position like an SUV makes me feel scary while driving or even traveling, especially at highways speeds. Anyways, seating position is different topic so leaving it here for now.

Last edited by tbppjpr : 5th October 2014 at 22:19.
tbppjpr is offline   (2) Thanks Reply With Quote
Old 6th October 2014, 05:53   #126
BANNED
 
Join Date: Nov 2008
Location: New Delhi
Posts: 672
Thanked: 118 Times
Default Re: Sheet Metal Thickness - Does it matter?

Quote:
Originally Posted by mayankk View Post
Please don't live by those words, and also, don't throw out such a generalization that the difference is due to thickness of the sheet metal....
I never said it is only to sheet metal thickness .I said thicker sheet metal on modern design cars is better than thin sheet metal modern design from strength , ability to dissipate energy at high speeds view point. Eg The ribbed roof seen nowadays will be much stronger if with same design it would have thicker sheet metal .

Last edited by Trust_In_Thrust : 6th October 2014 at 05:58.
Trust_In_Thrust is offline   (1) Thanks Reply With Quote
Old 6th October 2014, 09:40   #127
Senior - BHPian
 
IshaanIan's Avatar
 
Join Date: Aug 2012
Location: Hyd/B'lore
Posts: 2,009
Thanked: 2,196 Times
Default Re: Sheet Metal Thickness - Does it matter?

Quote:
Originally Posted by Trust_In_Thrust View Post
I never said it is only to sheet metal thickness .I said thicker sheet metal on modern design cars is better than thin sheet metal modern design from strength , ability to dissipate energy at high speeds view point. Eg The ribbed roof seen nowadays will be much stronger if with same design it would have thicker sheet metal .
And that is what the NCAP agencies are trying to tell you mate; it doesn't matter at all. At the speeds and resultant forces we are talking about, it is all down to the construction and internal structures. The sheet metal makes negligible difference.
IshaanIan is offline   (2) Thanks Reply With Quote
Old 8th October 2014, 05:52   #128
BHPian
 
Join Date: Sep 2014
Location: Pune
Posts: 131
Thanked: 48 Times
Lightbulb Re: Sheet metal Thickness- Is it a big deal?

Quote:
Originally Posted by CrAzY dRiVeR View Post
NCAP ratings judge how good the car can protect the cabin against external shocks. A lighter car can be as safe/ better than a car with stronger sheet metal- in the way it 'crumbles' itself to prevent the impact being transferred to the cabin.

But what about smaller impacts? Like a basketball hit? Or a bicycle hit? Have seen cars like the previous generation City takes quite a hit in such mundane cases. My uncle's old WagonR had its boot caved in when his school-going child leaned against it while trying to push another kid. With sheet metal offering little resistance- the car does what it does best- crumble.

Observe the cars around you. Personally I am of the opinion that the European cars age much better as they take fewer kinks from smaller shocks. My 75k run Punto still looks good whereas our WagonR was a mess with dents all around. Never even got to figure out how some of the dents were formed! The other car in our garage now is a brand new Hyundai Xcent and even that has picked up a deep dent from a mild impact!

Another angle to look at is in terms of torsional rigidity. Cars like the Swift for example don't 'feel' heavy but the figure seem surprising. The added extra unladen weight helps in making the chasis more rigid and fun to drive.

This is not to say that stronger sheet metal makes cars stronger at 60kph speeds, where NCAP tests are done. Design plays a major role here, but for your particular query- you also need to consider that fact that the City is a 2014 design but all the other cars like Vento, Linea, Fiesta etc are nearing the end of their current generation life cycle. The modern compacts fare better than even the biggies of not so long ago- that's the rate at which design and technology progresses.

An ideal combination according to me would a combination of the two. Good design along with strong sheet metal. Even if it might not be safer- but won't it contribute hugely to the feel good factor? Take the city itself for example- wouldn't it be nicer if it had the same design and efficient crumble zones, but better sheet metal so you don't get the feeling that the whole door is flexing if you bang the door a bit harder?
Thanks, this was an insightful and very informed opinion there. Yes, I never could think of connection between longer life and the sheet metal thickness!

It doesn't matter if you get 2 kmpl less fuel economy per litre, the longer life compensates for more than that! What's the use having a Swift/i10 etc that would age out at 80,000 or 1 lakh kms as compared to a Punto/Polo easily doing 1.5 lakh kms! One can save cost of another car altogether by this long life. Of course, I am not interested in deviating but the longer duration of time you drive your car, you know its characteristics and understand if it is going to give a problem or not, making it a very predictable deal.

Is that the reason why we see so less number of Maruti 800s, Zens, Omnis (consider the record sales figures) as compared to old Palios on city roads?!?
ameyawaghmare is offline   Reply With Quote
Old 8th October 2014, 12:03   #129
BHPian
 
Join Date: Dec 2013
Location: Gandhinagar
Posts: 121
Thanked: 281 Times
Default Re: Sheet Metal Thickness - Does it matter?

Quote:
Originally Posted by nakul0888 View Post
Here is my argument though. If the Japanese are able to make a considerably lighter car as safe as a heavy European car then aren't they the more brighter folks here. I mean a lighter car means better power to weight ratio, better economy, nimbler handling, basically better at everything. Sure you lose out on the novelty factor of a Vault like build quality and maybe the thicker sheet metal may help in case of fender benders. But is that more relevant than better performance of the car?
[/left]
Considering all things equal a car with thicker sheet metal will be safer and have better structural rigidity than a car with thinner sheet metal.

So it looks like a question of priority. For someone it might be nimbleness over safety.

Personally for me, there is nothing more reassuring than the solid door thud of a well made car. Considering that me and my family will spend a great amount of time in a car during which they are exposed to potential harm in more ways than one I would pick build quality over nimbleness any given day...

While attributes like power to weight ratio, nimbleness...even fuel economy are good to have they come way down in my list compared to safety and build quality...or even comfort.

There was a time not so long ago when cars were sold primarily on the attributes of safety, comfort and build quality. Till all those retired race drivers found employment with TV channels and Car magazines. Perhaps this is one of the reason words like 'understeer' are more heard on Top Gear rather than 'safety' and 'structural rigidity'.

My two pence...
BowMan is offline   Reply With Quote
Old 8th October 2014, 12:14   #130
Senior - BHPian
 
sourabhzen's Avatar
 
Join Date: Jun 2012
Location: GURGAON
Posts: 1,427
Thanked: 1,159 Times
Default Re: Sheet Metal Thickness - Does it matter?

Quote:
Originally Posted by BowMan View Post
Considering all things equal a car with thicker sheet metal will be safer and have better structural rigidity than a car with thinner sheet metal.
Is there any studies or data to support this statement? If yes, then my next car will have thicker sheet metal as well. Please share a link to the data for everyone's benefit, if available.
sourabhzen is offline   Reply With Quote
Old 8th October 2014, 12:27   #131
Distinguished - BHPian
 
saket77's Avatar
 
Join Date: Dec 2012
Location: Ranchi
Posts: 2,970
Thanked: 3,063 Times
Default Re: Sheet Metal Thickness - Does it matter?

Quote:
Originally Posted by BowMan View Post
Considering all things equal a car with thicker sheet metal will be safer and have better structural rigidity than a car with thinner sheet metal.
Sorry, but the NCAP says otherwise. Considering all things to be equal, the sheet metal thickness is NOT a criteria for safety. I have quoted this probably twice or thrice before in this same thread. I will do it one more time for you. And the door thud is not because of the metal, it is because of dampening rubbers. Also, I have not yet read someone who established that doors which do not close with a 'reassuring thud' are unsafe and open & throw out the occupants in case of accidents!

Quote:
Originally Posted by sourabhzen View Post
Is there any studies or data to support this statement? If yes, then my next car will have thicker sheet metal as well. Please share a link to the data for everyone's benefit, if available.
Saurabh, as I stated earlier, there are studies. But they point out to something entirely contradictory. The thickness of sheet metal has NO impact on the crash safety of the car as assessed by Australian NCAP. I will quote the source & the statement below:

Quote:
Q:Is the metal body thickness of any car a factor considered in crash testing and does the thickness have any influence on the results of a crash?

A: Modern car designs have a very strong passenger compartment combined with structures that are deigned to crush in a controlled manner. Exterior body panels have very little influence on these structures.
(Source: Australian NCAP; http://www.ancap.com.au/faqs)

Trust that seals the discussion of this thread this time. The question that this thread asks is do 'Sheet metal thickness matter (in terms of safety?)' I think that thread has the answer based on the extensive research and specialization that the NCAPs undertake. So, everything else remaining the same, external sheet metal will not have impact on the crash safety of the car.

Regards,
Saket

Last edited by saket77 : 8th October 2014 at 12:31.
saket77 is offline   (1) Thanks Reply With Quote
Old 8th October 2014, 12:35   #132
Senior - BHPian
 
sourabhzen's Avatar
 
Join Date: Jun 2012
Location: GURGAON
Posts: 1,427
Thanked: 1,159 Times
Default Re: Sheet Metal Thickness - Does it matter?

Quote:
Originally Posted by saket77 View Post
Trust that seals the discussion of this thread this time.
Thank you Saket.

This thread should be closed unless there are some new studies or research by an authorized and acknowledged agency. The discussion always sway towards European vs Asian cars in India instead of discussing scientific and established views on sheet metal thickness.
sourabhzen is offline   Reply With Quote
Old 8th October 2014, 12:40   #133
Distinguished - BHPian
 
saket77's Avatar
 
Join Date: Dec 2012
Location: Ranchi
Posts: 2,970
Thanked: 3,063 Times
Default Re: Sheet Metal Thickness - Does it matter?

Quote:
Originally Posted by sourabhzen View Post
Thank you Saket.

This thread should be closed unless there are some new studies or research by an authorized and acknowledged agency. The discussion always sway towards European vs Asian cars in India instead of discussing scientific and established views on sheet metal thickness.
Exactly Saurabh. If we do not look into Euro Vs Japanese, then the thread has reached the logical conclusion and I believe this is what the thread title asked literally. Comparison of quality of Euro Vs Japanese cars or structural design, integrity and safety is probably food for some other thread.

Regards,
Saket

Last edited by GTO : 10th October 2014 at 16:08. Reason: As requested
saket77 is offline   Reply With Quote
Old 8th October 2014, 22:54   #134
BANNED
 
Join Date: Nov 2008
Location: New Delhi
Posts: 672
Thanked: 118 Times
Default Re: Sheet Metal Thickness - Does it matter?

Quote:
Originally Posted by BowMan View Post
Considering all things equal a car with thicker sheet metal will be safer and have better structural rigidity than a car with thinner sheet metal.
Agree with you 100% . I also firmly believes it . I relate to thicker metal not just for outer body shell but for complete car .

The problem is most testing is done on old cars which used to have thick sheet metals vs newer generation cars so the older were doomed to fail .

The recent test wherein I20, Swift , Figo , Polo were tested proves that thicker sheet metal employed not limited to outside frame but chassis too play keen role in safety as if the foundation is weak the airbags dont really help .Thus putting airbags in Figo , Polo made them safer but was lost relevance in others due to weak underlying structures.

Also i feel why the cars from VW, FIAT , FORD etc have harder suspension is that the mounting points points can take the stress of resultant forces but in cars from basically Japan, Korea employ softer suspension to protect the mounting point/chassis from unnecessary forces/damages since they are just truly built to cost.A harder suspension will put higher stress on the mounting points/chassis which means the whole car will need to have greater strength compared to a softly sprung car.

Another thought i have is Japanese, Koreans dont have the kind of high speeds normally as in Europe , US we see so engineers first developed the cars for there own markets and then with time became a tradition to each on how a car should be made , with which parts / specifications . Possibly that is the reason why mainstream cars in US , Europe have higher displacement than Japanese, Koreans .

Note from Support - Please type in full English and avoid using short forms such as Japs for Japanese as it is racist and derogatory. Jap is a derogatory term that gained notoriety during WWII.

Last edited by n_aditya : 9th October 2014 at 10:53.
Trust_In_Thrust is offline   Reply With Quote
Old 3rd November 2014, 21:56   #135
BHPian
 
Join Date: Aug 2014
Location: New Delhi
Posts: 286
Thanked: 229 Times
Default Re: Sheet Metal Thickness - Does it matter?

One element that can tilt the balance slightly in favour of thicker sheet metal is that the weight of cars with thicker sheet metal would be higher by a few hundred kilos. Take a look the short video below from US Insurance Institute for Highway Safety where you would see a Toyota Yaris fare poorly when colliding with a Camry. The experts made this conclusion: "all other things being equal, people in larger, heavier cars would fare better than people in smaller, lighter cars". Although the size may remain the same and thus would negate this theory a little, the added weight of thicker sheet metal is bound to help to some extent.

Here is the video:

Lobogris is offline   Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
Modifications for Gypsy King - Does the sequence of modifications matter? khan_sultan Modifications & Accessories 18 6th September 2009 14:02
Does Power really matter or Experience? sumitkalindi Street Experiences 16 7th November 2007 15:41
Does it matter what “we” think? adya33 The Indian Car Scene 19 13th December 2006 14:36
Swift--Body Metal Thickness ivor Technical Stuff 15 6th May 2006 00:37


All times are GMT +5.5. The time now is 07:16.

Copyright ©2000 - 2017, Team-BHP.com
Proudly powered by E2E Networks