Weight difference alum. Vs steel hood (bonnet)

O

Old-Duckman

Active member
 SW Pennsylvania USA
I know that the E85 (probably other Z4 models ?) have an aluminum hood (bonnet). I verified this via a magnet on my car…

I have read that this was for weight reduction to keep the Z4 weight more inline with the Z3.

Ok so how much weight does it really save? My guess is that it probably isn’t very much, relative to the weight of the entire car. I was talking with my cousin about this and he felt that it was sort of an automotive trend during certain model years as he had a Ford Mustang that had an aluminum hood as well.

Anyone have any insight, specific knowledge or perhaps just a guess?
 
Well I wandered off to google and found some very rough calculators.
Assumed the bonnet was 1500mm x 1500mm x 3mm thick
Steel 53Kg
Aluminium 18Kg

Thanks for distracting me from a very boring day. :D
 
enuff_zed said:
Well I wandered off to google and found some very rough calculators.
Assumed the bonnet was 1500mm x 1500mm x 3mm thick
Steel 53Kg
Aluminium 18Kg

Thanks for distracting me from a very boring day. :D
Click to expand...
Unfortunately this comparison is not particularly valid. 3mm is incredibly thick for a hood. The hood wouldn't be that thickness in either aluminium or steel. It'd likely be slightly thinner in steel form. There are also reinforcements to consider. They may be engineered differently as the different materials likely would have different requirements.

I'm not sure if it was a fad but I think alum hoods are quite common. My 2012 F-150 had an alum hood.
 
Enuff_zed’s estimation was in the ballpark, realoem says the bonnet weights 11.0kg. That is probably primed, without paint. If we knew the total weight of the primer, we could do more serious calculations :)
 
jetrep said:
enuff_zed said:
Well I wandered off to google and found some very rough calculators.
Assumed the bonnet was 1500mm x 1500mm x 3mm thick
Steel 53Kg
Aluminium 18Kg

Thanks for distracting me from a very boring day. :D
Click to expand...
Unfortunately this comparison is not particularly valid. 3mm is incredibly thick for a hood. The hood wouldn't be that thickness in either aluminium or steel. It'd likely be slightly thinner in steel form. There are also reinforcements to consider. They may be engineered differently as the different materials likely would have different requirements.

I'm not sure if it was a fad but I think alum hoods are quite common. My 2012 F-150 had an alum hood.
Click to expand...
Seriously???
Which part of 'very rough' did you miss?
This was just an exercise to see if there was likely to be any significant difference or whether it was, as suggested, just a fad.
I'm guessing you're just being picky because I can spell aluminium. :poke: :D
 
All the above. Alu is about a third the weight of steel volume for volume, but steel is stronger so can generally be made thinner, so the practical difference is not three times. You could take the view that every little helps and a 5-10kg weight saving is significant.
In reality it’s a great marketing claim, given that the bonnet is the largest panel on the car, to say that it’s made of “weight saving” aluminium.
Environmentally, however, aluminium is much more destructive than steel (weight for weight) and much more expensive too.
 
So the E85 bonnet is about 9.67 kgs…(E89 14.5kgs)

Aluminium alloys are around 2.7 denser than water, alloy steel is around 7.8 times…

Using similar design techniques rule of thumb alloy needs to be about 1/3 thicker than steel..

So that 10kg bonnet would be around around 18.5kg…not allowing for washer pipes…
 
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