Tire Sizes????

[mpunklil]

Ok, I have been sifting through this entire forum trying to find out what the maximum size tires i can fit on my car are gonna be. I recently picked up some silver C6 rims, 18" front and 19" rear. Im shopping for Michelin Pilot Sport PS2's, and came up w/ the decision that the 305/30-19 for the back is going to be close to equivalent to the stock 235/55-16 as far as diameter is concerned. Only difference is going to be the obvious sidewall height and width of the tire. Is 305 too wide?? Do I need to make modifications with that size tire? If so, what is the maximum tire size (width) I can go w/o modifying anything in the back. Yes I plan on lowering it. Same deal w/ the front, but i was looking at a 275/35-18 tire. I basically want to go as wide as possible, w/o physical modifications. Im not worried about programming the ecu for now because I am open to tire series. Enough about everybody asking what rims are going to fit there f-body....lets talk common sense here and get some tire sizes. We all know any rim that is a 5x120 pattern and 16"+ will work on our cars provided the right offset or spacers.

[Doc99SS]

I do not like your tire sizes. The front tire is 0.5" bigger in OD than the factory tire, and the rear tire is 1.1" bigger in OD... Way too far off. I think that it would have been alot better to pick up 17" wheels for the front and 18" on the rear... But its too late for that. Before buying wheels, always check for an appropriate tire size. Also, as you go up in tire bead size, the price jumps quite alot.

You want tire Ods near 25.7" to 26.2". Smaller on front than the back. Max width of front tire should be 275mm, while the back 315 might just fit, but a 305mm would be better. I think that your front tire may rub.

[mpunklil]

i read that i could potentially get away with .5" difference in OD w/o needing the ecu reprogrammed due to ABS. I think you may have done your math wrong though, because the 305/30-19 is actually only .02" larger than a 235/55-16, and the 275/35-18 is actually .60" smaller. A 275/40-18 is .48" larger. So a 275 tire on an 18" rim is actually undesirable. BUT....a 265/40-18 is only .17" larger, which seems to be highly desireable in my opinion. Less risk of rubbing if 275's do actually rub (or come close). Unfortunately the 265 has a taller sidewall. the 275 is a better performance tire, so i would LIKE to fit that. Has anyone fit a 275 on the front? Also, I am currently running a 245/50-16, which is .53" smaller...and no probs w/ ABS

[Eugenio_SS]

actually, 5x120.65 will work... the 5x120 tend to have the lugnuts come loose.
I run 315/30-18s on all corners for daily use
I run 315/35-17s on all corners when racing
305s aren't too wide... but the 305/30-19 might be too tall, i'd try to get 25 instead of 30 to bring it closer to stock OD. 315/25-19 would be ideal.

[mpunklil]

305/30-19 is actually closer to stock diameter than 305/25-19. eugenio, what suspension are you running? and no rubbing w/ 315's all around at all?

[Eugenio_SS]

stock:
275/40-17 => 275mm x .4 = 110mm x2 = 220mm = 8.66" + 17" = 25.66"

my used sizes (street + race):
315/35-17 => 315mm x.35 = 110.25mm x2 = 220.5mm = 8.68" + 17" = 25.68"
315/30-18 => 315mm x .3 = 94.5mm x2 = 189mm = 7.44" + 18" = 25.44"

now the suggested sizes:
305/30-19 => 305mm x .3 = 91.5mm x2 = 183mm = 7.2" + 19" = 26.2"
315/25-19 => 315mm x.25 = 78.75mm x2 = 157.5mm = 6.2" + 19" = 25.2"

305/30-19 is bigger than stock size by 0.54"
315/25-19 is smaller than stock size by 0.34" giving more clearance.

I suggested 315/25-19, not 305/25-19
As for suspension, I have Ground-Control springs 500/150 w/ Koni DA on all 4, all rod-ends in the rear.

[Doc99SS]

The correct Camro bolt circle is: 5x4.75", forget about the metric stuff, its always been 5x4.75 as long as I can remember.

[Eugenio_SS]

The correct Camro bolt circle is: 5x4.75", forget about the metric stuff, its always been 5x4.75 as long as I can remember.

metric is the standard used by GM.
You are correct, though.... 4.75" = 120.65mm
The difference is subtle, but none the less, it's enough to get bolts loose regularly if running 120mm wheels

[mpunklil]

the bolt pattern was just suggested, i was too lazy too add in the other .65 since the topic of this post wasnt bolt patterns, it was tire size. i used the tire calculator on americastire.com