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The GT-C's are not a super light-weight wheel. From what I have seen, the stock 18's weigh 25-26 lbs. Even the forged monoblock TE37's and CE28's are around 20 lbs. in the 19" sizes. Maybe someone who actually has the GT-C's can verify, but they are probably around 25 lbs in those widths. With wider tires, I would say you will break even with the stock set up or possibly even be a little heavier.