Interesting that they say nothing about consumption. I would expect them to be less fuel efficient, but having some number to go by would be nice.
For a consumer product like this I think it's probably more important to compare the common case than the optimal case, because I know my tires often aren't in an optimal state, and as much as we could save as a nation by making sure tires were inflated correctly, we just don't, and I don't expect that to change meaningfully.
So I guess the question is how does 0.6% fuel economy loss on average for current tires compare to the loss in efficiency for using a Tweel, but according to some data from Michelin here[2], it looks like they're actually projecting them to be more efficient than current tires? I didn't read through the whole analysis, so I'm not sure, but that's what Table 7 looks like to me at a cursory glance and reading a few paragraphs in that section.
1: https://www.fueleconomy.gov/feg/maintain.jsp
2: https://manufacturing.gatech.edu/sites/default/files/uploads...
The money shot is here. Note that '5.5 kg/ton' refers to the rolling resistance of the tire.
> At this point the 5.5 kg/ton value is still only a design target, and this study serves mainly to confirm the environmental value of achieving that target.
Essentially, this conclusion is tautological. "If there were a tweel that had better rolling resistance than the best pneumatic tire on the market, then it will have a better fuel economy and environmental impact." Obviously!
I seriously doubt Michelin's tweel is anywhere close to that 5.5 kg/T mark. It's more likely something like 12 kg/T.
The purpose of this particular paper is not to show that tweels are better environmentally, it is to show an analytical framework for calculating the full-lifecycle environmental impact of tweels vs tires. Sort of like a "here are the equations, plug in real numbers later" kind of thing.
The authors of that paper did not intend to mislead -- this paper was published in 2011, likely written in 2010, only a handful of years after Michelin's unveiling of their gen 1 tweel design. To me, having been in the authors' position, I can easily tell what the true purpose of the paper actually was (the analytical procedure). But the authors had a secondary purpose driven by 'hype', almost, you could even call it click-bait: they wanted to make the tweel exciting so that other researchers would get interested in it and continue the work. One way to do that is by showing, from a materials perspective, that it is theoretically possible to design a tweel with a low rolling resistance, and given that, it's possible that tweels will be better for the environment over the full-lifecycle, including manufacturing and materials. And sure, this absolutely did/does deserve more research. However, the other issues with tweels, like NVH/comfort/etc, were 'out-of-scope' for that paper, and so they ignored those. Solving for those issues is what makes that 5.5 kg/T figure difficult/possibly impossible to attain.
When these papers are confined to academia, it all works out, because most of the people who read your paper are other people who are writing papers, and they get it. But once these types of papers are picked up by the press/media/general populous, they can be very quickly misinterpreted!
(To be clear, you didn't do anything wrong here, I'm just griping a bit about academia and pretending like I'm 'adding context' ;)
In some ways what you describe is a very common larger problem. When you want to promote something (whether it be because of financial or more altruistic reasons), its hard (possibly impossible) to walk the fine line for all people between accurately relaying information and convincing people of something less factual (such as "this is cool and we should look into it more"), namely because different audiences' relative experience in the area will mean they won't recognize where that line is in many cases.
For example, at exactly what point does a website or description for some open source project move from purely descriptive explanations of what it can do to promotion about why it's cool and why you should try it? People with different experience in the domain it's in will have difference experiences ready that info. The neophyte and the layman will interpret the statements differently.
The TREAD law does not specify when TPMS must alert, other than the tire being 'significantly underinflated'.
[1]: https://www.nhtsa.gov/sites/nhtsa.gov/files/fmvss/TPMSfinalr...
[1]: https://www.nhtsa.gov/sites/nhtsa.gov/files/fmvss/TPMSfinalr... (page 10)