stock 17s vs stock 18s

i have an 06 gt , just got the stock 18 inch polished bullits on my car, and i had the bright alluminum 17s on my car. does anyone know the weight differance ? and how much im possibly loseing in my 1/4 mile time ?????????thanks just wondering

Basing it on stock 17s and tires vs stock 18s and tires, there may not be much of a weight difference to really affect your 1/4 mile times. The biggest difference would be which one has the better traction. I've read numerous people getting sub 1.9 60' times with the stock 17" Pirellis! I could never get better than a 1.94 with the OEM 18" BFGs on the fanblades. I weighed my 18" 340CS(Halibrand style) with the Nitto 245/45-18 vs my 18" fanblade with the 265/40-18 MT ET Street and they were only a few pounds different. You really won't notice the weight difference until you step up to a wider wheel and wider and/or taller tires.

What difference do you notice after going to 18"s? Do the 18"s grip better/worse and/or do you notice braking distances being longer due to rolling mass?

I bought my GT w/ the base 17"s with the intent of immediately upgrading to 18"s but surprisingly enough, I like the 17"s...

My car came from the factory with 18" fanblades, but I run 17" charcoal bullitts for race days. The 18" with factory rubber weighs 54 lbs each, while the 17" with factory rubber weighs 48 lbs each, weighed on my bathroom scale. 6 lbs per wheel times 4 corners equals 24 lbs. While this doesn't sound like much, keep in mind that rotational mass has a much more profound effect on performance than static weight. Same reason people opt for lightweight flywheels, torque converters, and driveshafts.

so how much do u guys think im losing in the 1/4 mile ?

I have raced with the fanblades with the OEM 235/50-18 on all four corners and got a best of 13.34. Next time out I had the heavier, taller and wider Cobra 340SC wheels wearing Nitto 555 245/45 up front and 295/45 out back and my best dropped to 13.2s.
As five oh brian said, rotational mass reduction is good, but in the case of the stock wheels wearing the original size tires...I don't believe that weight difference will make much difference at all. The difference will be in the traction limits of each tire. In that case, I've seen the 17" Pirelli out perform the 18" BFG! Given that you could exactly duplicate the driving with both sets of tires, I'd guess the difference would be thousandths (.00X), maybe hundredths (.0XX)

So if I get some 18" Roush Trak Pak wheels that weigh 18-ish pounds each...I should be pretty awesome then?

Those would absolutely help depending on the weight of the tire you put on it.

kooldawg, what was the difference in trap speeds for those 2 runs?

I would think the larger wheels and tires would help during the first couple gears and then slow you down a tad down the last part of the track.

With the fanblades, 235/50-18 BFG (27.1") and full weight, my best trap speed run was 13.359@104.34.
My best trap speed with the 340C, 295/45-18 (28.3") (never ran full weight) was 14.132@107.62 (that had a 2.91 60' time) That gives the perfect example of how tire spin on the launch adds MPH. My best time that day however was 13.138@104.74 with a 1.965 60'.
My best trap speed with the fanblades, 265/40-18 MT ET Streets (26.5") at full weight was 13.099@105.49 with a 1.901 60'.
I did have a few more mods or different tune from one track day to the next.