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Anyone tried 235/50r18 size on gtp tock rims

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  • Anyone tried 235/50r18 size on gtp tock rims

    Was wondering do they rub. does it throw off your speedo? Better ride and handeling?
    6spd silver g6 is my daily driver. love the car too many problems

  • #2
    Glad someone posted on this, because I just put on a set of 235/55/16 Goodyears on my stock steelies (tires were free) and there is no rubbing at all. The car handles like a champ, even though they are only on the front. Understeer has vastly been reduced compared to the stock 215/60/16's. As far as throwing off your speedo, yes it will, at 60mph, your speedo wil show 59.13mph. With a set of 235/45/18 your speedo @ 60 will read 61.21mph.

    So, unless you get a tune, you'll have to settle with 1 mph over or under your actual speed. Heres a great site for calculating.
    http://www.dakota-truck.net/CGI-BIN/TireCalc.cgi
    2007 G5 Base Model
    Black 5 Speed

    Walmart - A store where you can buy a shot gun, ammunition, a ski mask, a baseball bat, a meat cleaver and map of the middle east, but you can't buy a CD that has a "Parental Advisory" sticker.

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    • #3
      someone has 245s on their GTP without rubbing so i doubt these will.

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      • #4
        I run 245/40-18s with no problem, and someone else on here runs a 255, but they are smaller diameter or the same as stock. The real question is why would you want to run a larger than stock diamter tire which will just make the car slower?
        04 CTS-V......like a G6, but with an extra 200hp, a proper transmission, and it is correct wheel drive:
        Self described crotchety old man!

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        • #5
          i drive 68 miles a day to and from work on wonderful ohio roads. i could use a little more sidewall for protection and smoother ride
          6spd silver g6 is my daily driver. love the car too many problems

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          • #6
            Originally posted by mbiker97
            I run 245/40-18s with no problem, and someone else on here runs a 255, but they are smaller diameter or the same as stock. The real question is why would you want to run a larger than stock diamter tire which will just make the car slower?
            make you slower? please explain.
            2008 Chevrolet Cobalt SS T/C
            Black/Black coupe

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            • #7
              Slower, maybe depending on which tire you chose, but were talking a difference of 1 mph or less at 60 mph... There really is no noticable difference.

              Remember though, the middle number in the tire isn't the sidewall size, its the aspect ratio. Width vs diamter of the tire (i think). Or something like that, but its not an actual measurement. if you want a softer ride, go for some 17's, but I think a 245/40/18 on stock suspension would still offer a nice ride.
              2007 G5 Base Model
              Black 5 Speed

              Walmart - A store where you can buy a shot gun, ammunition, a ski mask, a baseball bat, a meat cleaver and map of the middle east, but you can't buy a CD that has a "Parental Advisory" sticker.

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              • #8
                Originally posted by jerrodmann
                make you slower? please explain.
                You effectively raise your gearing by putting a taller tire on the car. It may not be by much, but it is there.

                The only real way to smooth the ride is to go to a smaller wheel with a proper sized tire. Of course I don't notice a harsh ride with my tires, even through Detroit and Chicago.
                04 CTS-V......like a G6, but with an extra 200hp, a proper transmission, and it is correct wheel drive:
                Self described crotchety old man!

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                • #9
                  are you guys nuts? 245/40r18 is almost 3/4 in shorter than stock. You will make your sabilitrak and your abs useless. you have up to 1/2" to work with. maybe a 245/45r18 would work but it is still almost 1/2 shorter.
                  6spd silver g6 is my daily driver. love the car too many problems

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                  • #10
                    Originally posted by 066speed
                    are you guys nuts? 245/40r18 is almost 3/4 in shorter than stock. You will make your sabilitrak and your abs useless. you have up to 1/2" to work with. maybe a 245/45r18 would work but it is still almost 1/2 shorter.
                    The aspect ratio don't mean the same measurement for every tire size. As the section width goes up (245mm), to keep the same diameter tire, the aspect ratio must go down. The aspect ratio is simply a percentage of the section width. If you have a 225/50r18, that means that the side wall of your tire is 50% of the 225mm section width.....or 112.5mm
                    If you have a 245mm section width with an aspect ratio of 45 would be 110.25 mm, or 5mm or about 3/16" smaller in the overall diameter.
                    Black 06 GTP Coupe - Dr. Speed Cold Air Box, Tinted Windows, Projektorz - Coming this week: Grafxworks Pontiac overlays all around, Black Painted Calipers w/ ZZP Decals and Rockblocker Smoked Tail Light Covers !!

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                    • #11
                      Originally posted by 066speed
                      are you guys nuts? 245/40r18 is almost 3/4 in shorter than stock. You will make your sabilitrak and your abs useless. you have up to 1/2" to work with. maybe a 245/45r18 would work but it is still almost 1/2 shorter.
                      Yes it is shorter, but there are zero issues when it comes to stabilitrak and abs. As long as all 4 tires are the same size there won't be any issues. If you start running 2 at one height and 2 at another the system wigs out. BTW I know this since my car has zero issues, and it's not just hearsay.

                      BTW tire heights:
                      stock 225/50-18: 26.9"
                      245/45-18: 26.7"
                      245/40-18: 25.7"
                      04 CTS-V......like a G6, but with an extra 200hp, a proper transmission, and it is correct wheel drive:
                      Self described crotchety old man!

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                      • #12
                        your welcome to your opinion but your wrong. just because you havent had issues you have been lucky. the specs from gm on this are very clear any more than .65 in will disable stabillitrack. your abs will work but not up to gm specs. I would be happy to hook you up with my uncle who is a master tech. also ore you using stock wheels? your tire size is not ment for a 7" rim. they are for an 8.5-9". look it up.
                        6spd silver g6 is my daily driver. love the car too many problems

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                        • #13
                          ok i will ask again since everybody seems to not answer the question I asked origionally. Has anyone run the 235/50r18s?????
                          6spd silver g6 is my daily driver. love the car too many problems

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                          • #14
                            Originally posted by 066speed
                            your welcome to your opinion but your wrong. just because you havent had issues you have been lucky. the specs from gm on this are very clear any more than .65 in will disable stabillitrack. your abs will work but not up to gm specs. I would be happy to hook you up with my uncle who is a master tech. also ore you using stock wheels? your tire size is not ment for a 7" rim. they are for an 8.5-9". look it up.
                            I'm not running a stock wheel. Also my friend is the one who designed/spec'd the abs/stabilitrack for our car.

                            I would like to call your uncle and talk to him, as his info is clearly not correct, or he is feeding you a line to best "that kid on the internet". Think about it for just a minute. There are zero airspeed sensor on the car. If all 4 wheels are registering the exact same speed, how would the car possibly know that that isn't correct?

                            BTW techs generally don't have resources like that (the 0.65" rule from above) whereas I do since I actually build the vehicles.

                            Oh and just because your "facts" piss me off:
                            My 245/40-18 is supposed to be on a 8-9.5" wheel.

                            http://www.avontyresusa.com/tires/tech_m550_as.html
                            04 CTS-V......like a G6, but with an extra 200hp, a proper transmission, and it is correct wheel drive:
                            Self described crotchety old man!

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                            • #15
                              Oh, did I just see pwnage there?

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                              Mobil 1 | Doctorspeed Stage 3 & 4 CAI | CRABS | Sacchi S45 245 Black 18" Rims | 6000k HID Headlights + Fogs | GT-R Exhaust | 20% Tint | Pioneer AppRadio 2

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