Er... not sure I understand what you mean by "moving up" if the diameter remains unchanged. You mean, get a larger rim but a tire with a smaller profile? Yes, you can do that, but depending on the rim and tire, it won't necessarily reduce your weight (and will likely increase it, actually).

You can actually move up even in overall diameter and still realize savings, yes, but the weight distribution is the important point here, and you're likely to save more by going lighter on the same size than lighter on a larger size. Basically, you want to both (a) reduce the overall weight of the wheel, and (b) keep as much of the weight as close to the axle as possible. In principle, you could even find a heavier overall wheel that still saves gas because the weight is concentrated near the axle, thereby reducing the moment of intertia (and thus the torque required to turn it). So yes, if you found a larger rim/tire combo whose weight distribution was more beneficial, you'd still save... but as I mentioned, it's easier to stay in the same size and go with ligher (alloy) rims and lighter tires. That way you don't have to do any calculations to figure out whether your proposed new wheel will work or not.

As for decreasing the size, you can still make the tire weigh more than the rim... as I mentioned, it's the overall weight distribution (size AND weight placement) that matters. I'll refrain from posting all the equations here but suffice it to say that none of these options is really cost-effective since new rims/tires will cost more than your gas savings. If you're buying new rims/tires *anyway*, then it's worth considering these factors. I would recommend simply staying with stock sizes but going lighter on the weight, it's the easiest solution if you're already buying new rims/tires. If not, don't bother.

You're quite welcome, that's what FT is all about. I don't know what the CSRs may have told you, but most of them seem unfamiliar with the terms of the specialty cards anyway. When I called them a couple of months ago, I had to point them to the T&Cs so they could figure out how the reverse tiers worked! (I had an issue where my tiers didn't reset on the anniversary date... they only reset 2 months later. No idea why and no idea if it will bite me again next year; I never got a call back from the CashBack department despite at least 4 attempts.)

From personal experience, I can tell you that the specialty cards still work just fine under the Get More promos. I definitely received the usual cashback plus the Get More bonus under the Home Improvement promo a couple of months ago using my Home Improvement card, and got the Get More bonus on bookstore purchases about 5 months ago using my Restaurant card. So both specialty cards have shown that they can take advantage of the Get More... unless something has changed since then. Hopefully it all still works as usual.

True, they don't always... but *usually* they do, and the cheaper stations may be harder to find and/or out of the way. If you're going to Costco anyway for your shopping, you may as well gas up there since driving out of your way to save an extra 1-3 cents per gallon is generally not worth it unless the cheaper station is also on your way. (If it's out of your way, you not only lose time, but you use gas to get there, hence decreasing or negative the savings.)

As for quality of gas, as others have said, it's mostly the additives... however, "purity" can be an issue. In principle, gasoline is supposed to be purely octane, hexane, and mandated additives (ethanol, oxygenation, MTBE [in the past], etc.) Even though all stations will meet the minimum requirements for gas in terms of octane rating and mandated additives, the no-name brands may have a higher water content in the gas, or may have other deposits and impurities, all while still meeting the minimum requirements. The gas will still work just fine, but over the long term may cause increased deposit buildup and/or engine wear (higher moisture in the gas can lead to increased sludge and corrosion in the cylinders). The name brands that add detergents (like Chevron, Shell, etc.) will also likely take care to "purify" the gas beyond the minimum requirements, to reduce water content and other impurities that won't affect the octane rating but can still cause certain problems over extended periods.

(Of course, adding your own detergents such as Slick 50, STP, etc. every few thousand miles can also reduce sludge and deposits, although it won't help fix corrosion if you've got it.)

That being said, I've been fairly happy with Costco's gas quality, whereas I've noticed engine knocks and pinging if I use certain discount brands such as ARCO... so I don't use them. Since I'm at Costco every other week, gassing up there is convenient and cost-effective, since in my area (Berkeley) they consistently have the lowest prices except for 1 or 2 stations that are either out of my way (and thus not worth driving to) or whose gas causes my engine to complain. If I'm in need of a fill and not near Costco, I'll put in some name-brand (usually Chevron) to tide me over until the next Costco trip.

Granted, I do need 91-octane or higher in my car (Subie WRX ), so it's more sensitive to deviations in the gas.