eXodus
Posts: 135
Joined: Tue Dec 22, 2020 6:06 am

Re: BMW i3 vs. Chevy Bolt -- Structural Efficiency ?

Sun Mar 14, 2021 12:12 pm

electrons wrote:
Sun Mar 14, 2021 10:20 am
Since the Bolt takes 7,000 lbs more force (to displace 5"), it's safer in rollover accidents. Junkyard surveys aren't accurate. Accidents vary.
As a firefighter cutting people out of "safe" vehicles I have to disagree with that. When I see a car that has a lot of good ratings but doesn't perform well when it really counts. I'm doubting the question the science is asking.

Does static roof strength really translate into dynamic rollover stability? My Thesis is no it doesn't - a bouncy ball is better in rolling down a hill then one made out of glass. The glass has probably 1000x more static force - but I'm rather inside the bouncy ball then in something crumbling apart after the first hit.

You are welcome to disprove my thesis and I will change my opinion on that if you lay down some facts.
Don't get me wrong here, this is not against the GM, I owned 3x GM vehicles over the years, a Chevy Express sits in my Driveway and is the most awesome REX you can image :P (got a i3 BEV and the Express is for long tours) and as soon that BrightFrop EV1 Van gets release I'm going to buy one.


Further, the skateboards: Yes depending on the definition BMW was not the first skateboard developed.
Yet, I think it was the first to market.

The Tesla Model S and even Volt does not count the since the "skateboard" is fully welded to the body and does not have any stability without. While you can drive the i3 with only bottom part. With that logic we could include every ICE car platform and call it skateboard.

Image

Lesterbmwi3
Posts: 33
Joined: Mon Sep 25, 2017 12:32 pm
Location: USA- NewYork

Re: BMW i3 vs. Chevy Bolt -- Structural Efficiency ?

Wed Mar 17, 2021 6:52 pm

In2014 according to car driver magazine bmw I 3 was 2600 lbs and is still faster than newest 2021 I 3 bc is a lightest from all of them and also a carbon fiber structure is 5 times stronger than steel and much lighter means replacing steel with carbon fiber is 5 x lighter I tested Bolt EV is no compromising with bmw I 3 different class I spin tires on Bolt all the time in Bmw I 3 you can’t do it is so well balanced Bolt weight 2017. Is 3563 lbs 2014 BMWI 3 weight 2635 lbs

frictioncircle
Posts: 141
Joined: Fri Nov 25, 2016 11:23 pm
Location: USA West Coast

Re: BMW i3 vs. Chevy Bolt -- Structural Efficiency ?

Thu Mar 18, 2021 1:33 am

Manufacturers list their vehicles' weights and magazines quote them.

Shortly after I purchased my 2014 i3 BEV I took it to a truck scale. With minimal user-added detritus (and NO driver), my 2014 i3 BEV weighed 2,880 lbs.

My opinion... I think BMW's claims of a sub-2,700 lb. curb weight were enabled by EU marketing regulations.

eXodus
Posts: 135
Joined: Tue Dec 22, 2020 6:06 am

Re: BMW i3 vs. Chevy Bolt -- Structural Efficiency ?

Thu Mar 18, 2021 3:07 am

frictioncircle wrote:
Thu Mar 18, 2021 1:33 am
Manufacturers list their vehicles' weights and magazines quote them.

My opinion... I think BMW's claims of a sub-2,700 lb. curb weight were enabled by EU marketing regulations.
In the EU the base weight of the vehicle is listed - means without any options. That means the absolute stripped base vehicle.

Very few vehicles ever get delivered that way. But the same is true for the Bolt (or any other vehicle). It's probably heavier then listed.
My Chevy Van is 600lbs heavier then the registration says - without driver inside.

electrons
Posts: 48
Joined: Mon Mar 21, 2016 4:49 pm

Re: BMW i3 vs. Chevy Bolt -- Structural Efficiency ?

Thu Mar 18, 2021 2:16 pm

frictioncircle wrote:
Thu Mar 18, 2021 1:33 am
Manufacturers list their vehicles' weights and magazines quote them.

Shortly after I purchased my 2014 i3 BEV I took it to a truck scale. With minimal user-added detritus (and NO driver), my 2014 i3 BEV weighed 2,880 lbs.

My opinion... I think BMW's claims of a sub-2,700 lb. curb weight were enabled by EU marketing regulations.
Very true. Yes, that is why the IIHS actually weighs their vehicles they crash test, and doesn't just trust the marketing dept. at BMW. :roll:
Your 2014 was 2,880 lbs, confirmed, not the mythical 2,600 lbs, and a 2017-21 weighs about 2,920, all from actual calibrated weighing from non-BMW scales.

It is odd BMW was cheating on their stated curb weight by 200 lbs. Sounds like they didn't want to admit they didn't succeed in reducing curb weight much. My numbers and analysis above is holding up well, and it says they got within about a 100 lbs of a Chevy Bolt on structural efficiency.

We engineers often use destructive testing and/or modelling to give insight into the physics occurring. For this, I noticed something interesting happening:
https://youtu.be/l6BKlWD24YQ

Notice the i3 loses it's tire & wheel, completely ripped off (small offset test). Comparing, the Chevy Bolt didn't lose it's tire, showing a beefier control arm. I think you would have to increase tire width & control arm thickness on the BMW i3 if getting the higher-range Bolt battery to handle the 300+ lb extra weight. Now our matching sized BMW i3, matching the Bolt's bigger size & mass, would need to weigh within 30 lbs or so to a Bolt, adding that effect to my analysis in previous posts.

alohart
Posts: 2339
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Location: Honolulu, HI

Re: BMW i3 vs. Chevy Bolt -- Structural Efficiency ?

Thu Mar 18, 2021 7:38 pm

electrons wrote:
Thu Mar 18, 2021 2:16 pm
Notice the i3 loses it's tire & wheel, completely ripped off (small offset test). Comparing, the Chevy Bolt didn't lose it's tire, showing a beefier control arm. I think you would have to increase tire width & control arm thickness on the BMW i3 if getting the higher-range Bolt battery to handle the 300+ lb extra weight. Now our matching sized BMW i3, matching the Bolt's bigger size & mass, would need to weigh within 30 lbs or so to a Bolt, adding that effect to my analysis in previous posts.
The i3's front suspension is designed to break during a small offset collision to prevent the wheel and tire from being pushed back into the passenger compartment. That doesn't necessarily imply that the Bolt's suspension is beefier (i.e., heavier) although it should be to support its heavier weight.

The REx model is 300 lb. heavier than the BEV model yet the wheels and tires are the same size except on an early Mega World BEV which had narrower (i.e., lighter) wheels and tires on the rear. So maybe you need to deduct some weight from the i3 to account for oversize wheels and tires on most versions.

Trying to compare weights that aren't known for certain, especially for components that are present on one car but not the other, seems like a very imprecise exercise. You're making so many assumptions that your comparisons don't seem very credible.
Aloha,
Art

2014 BMW i3 Arravani Grey, Giga World, Tech + Driving Assist, Parking Assist, DC Fast Charging, JuiceBox EVSE

agzand
Posts: 43
Joined: Tue Dec 22, 2020 3:00 pm

Re: BMW i3 vs. Chevy Bolt -- Structural Efficiency ?

Thu Mar 18, 2021 10:09 pm

Please stop comparing i3 to Chevy Bolt. Bolt is an econobox with FWD and torsion beam suspension. i3 is a luxury car with RWD and sophisticated suspension design. A Honda Accord is 196 inch long and weighs 3300 lbs. A BMW 330i is 186 inch long and weighs 3600 lbs. Using your logic all luxury cars are extremely inefficient. Except that when you get inside, shut the door and get going a BMW feels like it is carved from a single piece of steel, while the Chevy or Honda feels like the econobox that it is. You cannot get that feel from the chassis unless you add weight.

eXodus
Posts: 135
Joined: Tue Dec 22, 2020 6:06 am

Re: BMW i3 vs. Chevy Bolt -- Structural Efficiency ?

Fri Mar 19, 2021 3:08 am

electrons wrote:
Thu Mar 18, 2021 2:16 pm
Notice the i3 loses it's tire & wheel, completely ripped off (small offset test). Comparing, the Chevy Bolt didn't lose it's tire, showing a beefier control arm. I think you would have to increase tire width & control arm thickness on the BMW i3 if getting the higher-range Bolt battery to handle the 300+ lb extra weight. Now our matching sized BMW i3, matching the Bolt's bigger size & mass, would need to weigh within 30 lbs or so to a Bolt, adding that effect to my analysis in previous posts.
Start looking at the NCAP/ADAC crash test.

https://www.carcomplaints.com/Chevrolet ... 19/safety/

Image
The structure of the bolt collapses and you got intrusion into the passenger space

https://www.youtube.com/watch?v=4uivh0yegFk



vs.

https://www.carcomplaints.com/BMW/i3/2017/safety/
https://www.dailymotion.com/video/x312xcm



look at the top down view of the side pole test - chevy - collapse - i3 bounces off
https://www.youtube.com/watch?v=q7F6PcYZaiM
https://www.youtube.com/watch?v=U0VR35bhzVo

That's what I'm seeing in the Junk Yards - lots of flattened bolts

Image


So my opinion is still that the i3 is the safer and more sturdy car. Maybe not as light as it could be - but a good design for the time (2012)

electrons
Posts: 48
Joined: Mon Mar 21, 2016 4:49 pm

Re: BMW i3 vs. Chevy Bolt -- Structural Efficiency ?

Fri Mar 19, 2021 6:17 am

There's not much difference in the safety level of the BMW i3 vs. the heavier Bolt.

............Add mass to the BMW i3 to equal the size & battery mass (with ancillary structure for the new 960 lb battery), and the crash tests may begin to degrade a bit for the i3. The i3 could be beefed up to handle it though.

It would be nice if BMW would widen the i3 by a couple of inches to equal the size & interior volume of a Bolt, and then give it a 258 mile range battery to see what could be extended on that basic CFRP structure. As of now, the i3 is the size of a Ford Fiesta, and the weight savings of the i3 look good compared to the Fiesta, just not the Bolt.

The junkyard pictures above don't show a collapsed Bolt roof, only partially down, & it can take 7,000 lbs more force (iihs.org) than an i3 currently.
Also, we don't know what the Bolt at the junkyard has gone through.

The pole test eXodus posted above shows adequate Bolt safety there. Both the i3 & Bolt don't show any glaring problems.
Ditto with the IIHS side impact test, both similar.
Both are decent enough. You never get perfection, as you can even run those collisions at higher (1/2)mv2 levels & get more destruction.

I don't view 2012, when the BMW i3 design was finalized, as another "era" as eXodus does. 2012 was not the Dark Ages for engineering, unless you count the GM structural engineering blitz they did about 6 years ago, which is where eXodus could be correct about 2012 being backward-times at BMW. .... Young people view 2012 as ages ago, this is true. .... CFRP was used in 1981, my 2nd year in engineering school. I programmed my own Finite Element Analysis (FEA) CAE in structural design class in 1983, and used NASTRAN FEA CAE tool a little in 1984, so these are old technologies. (My work after that has been in vibrations, controls, A.I., algorithms, software, simulation, meaning I'm remembering all the fundamentals in FEA & structures again!)

It is certainly true they are doing more with design optimization & computer power, which contributes to GM's Bolt structure. They have iterated the steel stampings & weld points millions of times on computer models before commiting to metal, evolving the shapes as much as possible.
As I've investigated this from the outsider viewpoint, a picture is beginning to emerge of GM's extra structural engineering investments.

GM has blitzed this structural tech in the past 6 years, an effort that looks like it has advanced the tech. Best explanation I can find of what is going on here. How else do you hang a 960 lb battery brick in a Bolt belly & still look decent on overall mass & crashworthiness?
https://www.caranddriver.com/news/a1534 ... he-future/

eXodus
Posts: 135
Joined: Tue Dec 22, 2020 6:06 am

Re: BMW i3 vs. Chevy Bolt -- Structural Efficiency ?

Fri Mar 19, 2021 7:25 am

electrons wrote:
Fri Mar 19, 2021 6:17 am
The junkyard pictures above don't show a collapsed Bolt roof, only partially down, & it can take 7,000 lbs more force (iihs.org) than an i3 currently.
Also, we don't know what the Bolt at the junkyard has gone through.
I agree the bolt can take 7000lbs more static force ONCE.
But how OFTEN can I hit with 5000-10.000 lbs of force?

What I see is a bashed in frame at the Bolt and an somewhat intact frame at the i3. The frame at the i3 bounces back into shape - and is ready for the next hit. Which is what usually happens in a roll over scenario. You car hardly ever only flips once.

Another Great roof strength vehicle out the GM catalogue :
A Silverado has about 10.000lbs more roof strength as the i3 -

Image

I fully acknowledge that you can build great cars with High Strength Steel. Volvo does for example, they are just not very light.
And I think super light is not that important anymore with larger batteries and AI to calculate Aerodynamics.

Tesla gets better miles/kwh with a heavier car then both GM and BMW.

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