Tire size and weight?

You'll need to know the overall weight of both. More metal means more weight but at the same time you are getting less rubber. Now; rubber is lighter than metal, but many metal alloys are quite light, close to that of rubber. And when considering how much rubber there is - you have to figure the mass of the rubber as well.

As one goes up the other goes down. Somewhere there's got to be a trade off value. But if you're looking for better mileage you would be better served to find a tire that has a harder compound as they roll better. Considering weight matters nought when everything is in motion. According to Sir Isaac Newton an object in motion tends to stay in motion unless acted upon by another force. So once the tire is rolling you aren't spending any more energy making it roll. Rather, you are combatting the age old foe of efficiency - friction. There's friction caused by the rubber being compressed as it rolls along, friction caused by bearings, friction being caused by the very air you are moving through.

The more you reduce friction the better efficiency you get out of your fuel. Weight is not the same as friction. It takes energy to get it moving but once it's moving (aside from friction) you spend no more energy on it. That's why highway driving nets better gas mileage than the stop and go driving in the city. One opposite to that is the Toyota Prius. It gets better city mileage because they use the kinetic energy (mass of moving vehicle) to generate electrical energy and stored in the battery every time you stop the car. It's called active energy recovery.

In a normal car, you step on the gas, expend energy creating kinetic energy (motion). When you come to a stop light you convert that kinetic energy into heat (caused by the brake pads rubbing - friction again - against the brake rotor). Heat energy is wasted into the atmosphere. You can not convert that heat energy back into kinetic energy (motion).

I'm sure you didn't want to hear all this, but I gave you this much because you show signs of intelligence that is increasingly rare. MOST people don't think about these things. So being you are intelligent I figured I'd give you a little more to think about. Who knows! Maybe you'll be the next person to solve our energy problems.

Hope this helps.

'av'a g'day mate.

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Yes and no. Everything depends on the material of the rim. If the rim is heavier then yes. If the rim is lighter then no.