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      08-18-2011, 08:10 PM   #67
han405
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I somewhat agree.. in a car crash, the bottom line is I would prefer the car's structure crumbles and flexes around me by absorbing most the impact energy rather than having a rigid body that deforms little, meaning transferring most of the impact energy into ME.

In a car crash, I could careless how much damage my car sustains. There are always more M3s to buy, but I only come with 1 set of body parts, on top of that, only a few can be replaced and/or repaired but without ease.

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Originally Posted by bruce.augenstein@comcast. View Post
How so? "Torsional rigidity" describes resistance to body flex under load, such as when your right front wheel hits a bump. When that happens, the body will flex by some amount as the right front "bends up" under the load. More torsional rigidity, less body flex. Suspension engineers like this because they don't have to compromise suspension settings as much, and are free to pay more strict attention to ideal compression and rebound rates. Drivers tend to like this as well, because the car feels more of a piece from behind the wheel.

In my opinion, BMWs tend to have the best ride/handling compromise, model by model, partly because they are rigid.

However, all this said, there is no direct correlation between torsional rigidity and crashworthiness.

None.

The absolute best you can say is that a vehicle with a very good torsional rigidity probably needs a fair amount of material to make it so, therefore intrusion into the cabin in a particular accident may possibly be less likely. In addition, the extra weight is never a disadvantage in a collision, and will often be an advantage, as previously mentiond.

However, you could also say that a vehicle with very good torsional rigidity might in fact be naturally more dangerous to its occupants, assuming more material in its construction, because you need a bunch of "crush" in order to ease the G load on driver and passengers.



Answer: I have no idea, and neither do you.

Imagine the Bugatti is infinitely rigid, and the only thing that happens when you hit a tree is that the paint gets blemished. In that case, the occupants would almost surely die because of the massive G-force spike they would undergo.

Ideally, the Bugatti would crush right back to the firewall in that collision, meaning it stops from 50 in, say, four or five feet. This is infinitely better than it coming to a halt in zero feet. Capiche?

In the Z3, BMW has designed it such that in a 50 mph tree hit, the front end would crush (including any subframe materials), the engine would drop down (so it wouldn't smash back into the cabin), and the car would shorten itself up back almost to the firewall. This is how you maximize occupant safety. In effect, you weaken everything up except the passanger nacelle - and torsional rigidity is pretty much a non-issue in this circumstance.



This is simple nonsense. As already pointed out, this isn't how it works.



"Strong" really isn't the issue. In the aforementioned 40 mph head-on between the Smart Car and the Suburban, the Suburban would slow down to, say, 25 mph, while the Smart Car would go into instant reverse at 25 mph. Imagine the G forces when going from 40 mph to minus 25 mph in roughly the blink of an eye, compared to going from 40 mph to 25 mph in roughly the blink of an eye.

If the Smart Car were infinitely rigid, the results would be even worse for the occupants, because crush zones mitigate peak Gs, as is obvious and and has already been mentioned.
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      08-18-2011, 08:14 PM   #68
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One problem of getting a small car is you get a small or pathetic engine. You will never see an exciting engine in a 1 series bimmer.
But won't a 1M will beat an M3 in a straight line? Hell, I've run dead even with an E90 M3 up to triple digits in my stock 135. Ill take real world performance and driveability over high rpm antics anyday.
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      08-18-2011, 08:20 PM   #69
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      08-18-2011, 08:38 PM   #70
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Has anybody thought about just going back to smaller cars. The 1M is larger than the E30 M3. Look at how big the 5 and 7 series have gotten. If you combine new efficient engine technology with new lighter materials technology AND make cars smaller like they used to be, just imagine what you could accomplish in terms of fuel economy, emissions, and all aspects of performance. I still don't fully understand why manufacturers continue to make cars bigger and bigger. I thought the e39 M5, for instance, was very nicely sized. Why did it have to get so much bigger?
100% correct. I have no idea why vehicle size has continued to increase over the e46/e39/e38 generation. Those cars were correctly sized to the usage requirements for nearly all buyers (if not a little on the large size), but with the continued ballooning of vehicle size & girth at each level things have become absurd to the point that a large number of components are required to be aluminum or composites to meet the performance metrics of the vehicle.

My old e46 m3 fit everything from mountain bikes to multiple snowboards all while providing passengers with adequate space, comfort, and safety. IMO the 3 series should never have grown larger or heavier than that chassis.
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      08-18-2011, 08:44 PM   #71
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i've been saying this for years....as long as americans/the world gets fatter and fatter, car companies will continue to accommodate them. our cars will get bigger just to ppls' fat asses.

hopefully cf tech will trickle down quicker...
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      08-18-2011, 08:46 PM   #72
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Audi saying next A4 will be 300lb lighter.
GM saying next C7 vette has a target weigft of 3000lb with 5.5 DI v8 on tap with same 440hp.
I am a big fan of 1M and next gen 2M - its smaller, lighter and nimbler.. More of a purist car. M3 is more of a GT car these days.. 3800lb car is way too heavy to be called a sports car.
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      08-18-2011, 09:16 PM   #73
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Quote:
Originally Posted by Serious View Post
100% correct. I have no idea why vehicle size has continued to increase over the e46/e39/e38 generation. Those cars were correctly sized to the usage requirements for nearly all buyers (if not a little on the large size), but with the continued ballooning of vehicle size & girth at each level things have become absurd to the point that a large number of components are required to be aluminum or composites to meet the performance metrics of the vehicle.

My old e46 m3 fit everything from mountain bikes to multiple snowboards all while providing passengers with adequate space, comfort, and safety. IMO the 3 series should never have grown larger or heavier than that chassis.
They want them to get bigger so they can squeeze more models into the lineup
Audi got the A1,A3 etc
BMW got the 1 series
MB got the b class and a class etc

I know my e30 m3 fit 5 people comfortably and had a decent size trunk
So what did I gain by going to a e92?
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      08-18-2011, 09:54 PM   #74
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IMO the 3 series should never have grown larger or heavier than that chassis.
I don't know if this is BMW's fault... Every other manufacturer making bigger and bigger cars.. If 3 series stayed at the same size, it would sell maybe 20% of what it sold now..
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      08-18-2011, 10:30 PM   #75
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Originally Posted by bruce.augenstein@comcast. View Post
And by the way - none of this directly relates to torsional rigidity as an important part of occupant safety, because it is of little consequence in that regard. More torsional rigidity is a good thing, but it's not a safety issue.
I'll agree with you and leave it here. I understand your points and I guess I was wrong to say that "more" torsional rigidity equals "more" safety.

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I thought the e39 M5, for instance, was very nicely sized. Why did it have to get so much bigger?
I completely agree. I feel that the E39 M5 is the perfect size sedan. It's crazy how my E90 M3 is almost as big in every aspect. Personally, I'd love to be able to buy a new M3 from the dealership that is the size and weight of the E46 with the S65 V8.
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      08-18-2011, 10:40 PM   #76
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At the beginning of the 70's this same conversation was happening. The end of horsepower!! OMG, the end of driving fun.
Cars now are more fuel efficient and have way more horsepower. They are also infinitely more safe and reliable. Manufacturers will produce a product that meets the needs of their paying customers. It may take a few years but they will be on track in no time. Same reason they make cars bigger and bigger every year. People fall in love with a car and then ask for more room for the next model. Next model gets bigger. If you don't want a brand new 3 series because it's so big then buy an old one. Or buy a 1 series. Whatever.
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      08-18-2011, 11:45 PM   #77
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Quote:
Originally Posted by ra2fanatic View Post
i've been saying this for years....as long as americans/the world gets fatter and fatter, car companies will continue to accommodate them. our cars will get bigger just to ppls' fat asses.
+1

Car companies exist to sell cars, lots of cars.

Fit, educated people have fewer kids later in life.

Average americans as shown in Figure A, will be grandparents before any of us finish graduate school. The future is ineveitable.

Figure A
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      08-19-2011, 01:24 AM   #78
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The first salvo cracked me up. BMW simply lost its way through the years. Vehicle produced during boom times are typically larger with larger displacement and more horses, as do vehicles produced during recession that are more efficient and lighter in weight. It was all about the muscle cars during the 60-70s but all changed during the oil crisis, at which point Japanese were able to gain a foothold with their more efficient design and started a trend towards smaller cars in the 80s. The original M3 was a superb car because of its light weight, great chasis, and feedback compared to its larger displacement rivals.

BMW got caught up in corporate growth, pumping up revenues, expanding line up to please shareholders and management types and lost what made it great. (Like many others: Toyota, Starbucks...) Pushing more hp out of an engine is a lot easier to researching and discovering new materials or reuse of old material for less weight. It's interesting to point out those companies, like Lotus, who stayed small but remain true to its core values. We will see if BMW is able to return to its true values, not just following the herd because EPA require it to.

Car designs follow the economic cycle, though a lagging indicator. In a decade or two we will be back into power wars.
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Last edited by Robert; 08-19-2011 at 01:31 AM.
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      08-19-2011, 01:25 AM   #79
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Good article. I agree we will see more of a focus on light weight vehicles coming soon. It seems like the natural transition at this point
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      08-19-2011, 01:36 AM   #80
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Quote:
Originally Posted by han405 View Post
I somewhat agree.. in a car crash, the bottom line is I would prefer the car's structure crumbles and flexes around me by absorbing most the impact energy rather than having a rigid body that deforms little, meaning transferring most of the impact energy into ME.

In a car crash, I could careless how much damage my car sustains. There are always more M3s to buy, but I only come with 1 set of body parts, on top of that, only a few can be replaced and/or repaired but without ease.
LOL I would rather crash through the other car like a tank and not feel anything.
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      08-19-2011, 05:15 AM   #81
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Quote:
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At the rate things are progressing, a good deal of the CFRP savings will be offset by batteries and other equipment associated with the slow but sure transition from combustion engines to electric motors. i3 and i8 will bear this out.
I was talking with an electrical engineer here at my work. He brought up a good point when it comes to this electric craze. Now I'm no engineer so take this at a loose translation. He basically said that the problem with electric drivetrains is the amount of BTUs of energy used to move an object with drag and weight. That is a constant. More weight and drag, more BTU's etc. In his argument, gasoline is by far the most efficient fuel source. It takes far less material (gasoline) to produce a BTU of energy than it does for electric drivetrains. It's a physics problem. Electricity has to be stored, more BTU's means more storage. More storage is more weight, thus requiring more BTU's. The sweet spot is tied to the weight and that won't change.

His point was that an electric vehicle will never be as efficient as a gasoline vehicle in true terms of efficiency. He said efficiency is the wrong word to use. It is material savings meaning, saving gas. Electric cars save gasoline, but they are not more efficient. In fact they are far less efficient and far less flexible to be efficient.

Hybrids on the other hand are a better option for real efficiency. Storage (and weight) can be limited because regneration of electric BTU's can be siphoned from the BTUs produced by the gas engine. Funny though he comments that the gas engine in a hybrid can not only propel the car, but also recharge the electric drive. Jokingly saying you need a gas engine for an electric car to make an electric powertrain efficient.
Electric power is foolish.
It is the Betamax of fuel sources
15yrs we will have a large number of hydrogen powered vehicles on the road.

No body looks at the embodied energy of producing the batteries, generating power and lugging extra weight around. And these battery packs only have 10 year life spans!!

The sooner the US and UK stop chasing this foolish electric vehicle craze and focus on a commercial solution to hydrogen fuelling, the sooner (the US) will be back to a AAA rated economy!
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      08-19-2011, 05:55 AM   #82
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reducing the weight and get more horse power looks great...
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      08-19-2011, 08:05 AM   #83
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this will be hard to do as what drives up the weight in cars these days is not the engine or the construction materials or the process they employee. its mostly bc of government and automotive regulations that weight goes up. safety features, and more technology in comfort and passenger protection.
Think if we didn't have motorized leather heated/cooled seats? those things weigh a ton on their own. So i don't see weight going down significantly, but there could be methods where we can maintain the current weight or cut it down just a bit. Until carbon fiber production becomes cheaper there won't be cheap solutions to this.
The current M3 motor is lighter than the 3.2L i6 it replaced but the car is heavier still. (partially due to the fact that they made it bigger to please the market need for bigger cars and partially b/c of added safety and comfort features).
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      08-19-2011, 09:13 AM   #84
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Quote:
Originally Posted by MenTul View Post
+1

Car companies exist to sell cars, lots of cars.

Fit, educated people have fewer kids later in life.

Average americans as shown in Figure A, will be grandparents before any of us finish graduate school. The future is ineveitable.

Figure A
Hey who said you could put my picture up there?

The starter of this thread failed to specify that pounds per HP refers to the weight of the driver and passengers.

Would you rather have 414hp + 3800lbs (car) + 1000lbs (fat man + wife and 2 fat kids).

or 414hp + 3800lbs (car) + 700lbs (trim man + shapely wife and 2 fit kids)?
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      08-19-2011, 09:29 AM   #85
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Originally Posted by darksilkx1 View Post
Hey who said you could put my picture up there?

The starter of this thread failed to specify that pounds per HP refers to the weight of the driver and passengers.

Would you rather have 414hp + 3800lbs (car) + 1000lbs (fat man + wife and 2 fat kids).

or 414hp + 3800lbs (car) + 700lbs (trim man + shapely wife and 2 fit kids)?
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      08-19-2011, 09:33 AM   #86
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this type of thread comes up every few months like clockwork, with the same bitching about heavy new BMW cars, yet looking at your profile, a lot of you are the ones financially supporting these heavy cars and thats what BMW bases their priorities on
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      08-19-2011, 09:37 AM   #87
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this type of thread comes up every few months like clockwork, with the same bitching about heavy new BMW cars, yet looking at your profile, a lot of you are the ones financially supporting these heavy cars and thats what BMW bases their priorities on
Yes and no. What else these people can buy? C63 AMG is not any lighter. RS5 is the same story. They can keep their old cars, but that's highly unlikely.. So BMW know people will buy their cars, since all the other manufacturers are also getting bigger and heavier..
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      08-19-2011, 09:39 AM   #88
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The current M3 with about 500lbs shaved off of it would still need nearly 414hp to achieve the same top speed. Above 120 mph or so, weight becomes almost negligible as the aerodynamics of the car start to be the biggest factor is top speed. Obviously, lighter weight helps a ton with acceleration under 100mph and cornering/braking at any speed. My point is, give me a few hundred pound lighter car, but keep the same HP!
I think the best (and fastest) example for this is the McLaren F1 vs Bugatti Veyron drag race:

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