Can you expand on this? It seems to me (admittedly an outsider) that CF tubbed cars have dropped dramatically in price in the last 5 years, with two examples now below $60k with further price reductions rumored.
Obviously it's not going to be as cheap as steel any time soon, but how much of a premium can be sustained based on purely economic factors (TCO parity essentially) vs the performance/vanity segment the 4C/i3 currently reside in?
Viper GTS
The
basic fuel cost calculation is fairly straight-forward: for every 10% of the GVW eliminated a 7% fuel savings is realized (this number can be between about 5% and 8%, but 7% is a decent rule of thumb). Take a car that gets 30mpg (average mid-size sedan, ish) gets driven 15k/year (maybe a little above average) gas that costs $4/gallon (a little higher than what I see) and lets say it weighs 3500lbs.
Doing a bunch of math, that car consumes 500 gallons/year at a cost of $2k/year. If the car is light-weighted by 1lb it saves $0.40/year. Over a 15year life-cycle, assuming a 5% rate of return (i.e. a conservative rate of return on an investment like a 401k) that first light-weighted pound has a net present value of $4.34. That is to say if you could lose that pound for an initial cost of $4.34 or less, you would re-coupe the investment within 15 years. Note that I did this with VERY CONSERVATIVE inputs. If one assumes a 10% rate of return and a lifetime of 10 years the NPV of light-weighting drops to $2.30/lb.
Speaking in
very rough numbers:
It would take about 1lb of titanium @ $25/lb (raw material) to replace 2lb of steel for a net savings of 1lb at a cost of $25. Not worth it. Applications where corrosion is a limiting factor (exhaust) or reducing reciprocating mass is essential (i.e. connecting rods, valves, valve springs) may be viable, but require very careful analysis.
It would take 3lbs of 5xxx aluminum @ $3.50/lb (raw material) to replace 4lbs of steel for a net savings of 1lb, at a cost of $10+. Not worth it generally, but depending on the use of cheaper Al alloys, removal of other manufacturing processes such as painting and galvanizing, etc. it can be worth light-weighting with aluminum.
It would take 1lb of HSS (high strength steel) @ $0.50/lb to replace 2lbs or so of 'normal' mild steel, at a cost of $0.50/lb of material removed. Very much worth it in virtually all structural applications except where limited formability of HSS prohibits part manufacture.
I haven't done much work in light-weighting with CF, but this study has:
http://www.rmi.org/RFGraph-carbonfiber_vs_steel_manufacturing
Ostensibly CF would have to cost less than $4-5/lb to be cost-competitive with steel, excluding its lack of repair-ability, panache for catastrophic failure, and issues with galvanic corrosion of adjacent metallic components. Right now it costs around $16/lb, so it has a LONG way to go.
Now... there are more things to consider that just fuel economy, but for passenger vehicles it tells most of the story. I am obviously over-simplifying some things (i.e. there are some niche applications where more exotic materials may be cost-effective over a long life-cycle) but this is general gist of the economic arguments for light-weighting right now. That is to say: HSSs are great, aluminum can be useful, but any material much over $4/lb (CF, titanium, MMCs, high-end Al alloys, etc) is only used for cache or media hype, or where the customer is willing to pay a premium for the performance benefit and doesn't really care about fuel economy (and despite what all of us car guys want, this is a very small market segment).