[lunarhighway]

they would save gass, as they'd have less frontal area, and perhaps less rolling resistance, and they're rated for low speeds only! BUT
these tires are not intended to be ran more than once at low speed, so likely they'll wear very fast,

also since theyre only intended to replace one wheel, they likely rely on the remaining 3 good tires for a minimum of traction and handling.

so a test with these little tires would likely prove that their small frontal area and perhaps lower rolling resistance would be a big advantage, but they where unsuited for higher speeds and wouldn't last very long, give the car an indeed very dangerous handling and have a much longer brakeing distance.

if you take that space saver and try to alter it's negatives, giving it more traction, durability etc, you"d likely end up with a normal slightly skinny tire

so while it would be a theoreticaly interesting test, i doubt it would have any practical use, unless your a tire developer...

so as a test this would be interesting. but i dont think anyone in its right mind should considder these space savers as a valid fe friendly alternative for real tires