it all depends on the driving you do. they wont do anything for highway driving but you might get less than 1mpg in city driving. its hard to quantify.
anyway to answer your question, 2-3mpg is beyond way to optimistic.
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don't waste your time or time will waste you
I noticed around a 2mpg increase when I switched my two front 175/70 snow tires on steel rims, back to my 165/70 tires on vx rims, it's the best comparison I can give.
I've been looking for VX rims for a while, most of the time one of them is curbed or the seller wants to much for them....then theres shipping....where did you get them/how much? Mak
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'85 CRX Si Original EW3 @ 254k...suck it Detroit
'89 CRX HF-Z1 ~ When haste is needed
'97 Civic DX Hatch ~ Formerly 600hp, now 0hp, soon 115hp.