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What tire size do you run on 18" wheels?

This is a discussion on What tire size do you run on 18" wheels? within the Tires & Wheels forums, part of the W Body Tech category; Kinda confused... I'm looking for 18" wheels for a 2006 GP. Tirerack recommend 235/50-18 for either a 7.5" or a ...

  1. #1
    SE Level Member Jochen's Avatar
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    Default What tire size do you run on 18" wheels?

    Kinda confused...

    I'm looking for 18" wheels for a 2006 GP.

    Tirerack recommend 235/50-18 for either a 7.5" or a 8" rim.
    Superbuytires recommend 235/40-18 for a 7.5" rim.

    Both tire sizes I don't like.

    Can I do a 245/45-18 on a 7.5" or 8" rim?

    If you go with 18", what tire size do you drive?

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    SE Level Member cannon's Avatar
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    Default Re: What tire size do you run on 18" wheels?

    245/45R18 is what i had. I didnt have them very long(a week) but they never rubbed. And the gp guy i sold them to never had them rub.

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    Donating Users NegativeOne13's Avatar
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    Default Re: What tire size do you run on 18" wheels?

    I'm running 225/45 on front and 245/40 in back with no issue on 18"x8"

    And smile it's Blacktooth Grin!

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    SE Level Member Jochen's Avatar
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    Default Re: What tire size do you run on 18" wheels?

    Thanks so far Guys :-)

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    GT Level Member AdamBall's Avatar
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    Default Re: What tire size do you run on 18" wheels?

    i run 245/45 on a 18x8.5 rim with a 35 offset

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    Donating Users Silver GTP's Avatar
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    Default Re: What tire size do you run on 18" wheels?

    245/45/18 on 18 x 8 wheel

    2002 GTP: GMPP Sway Bars, BMR trailing arms, KYB AGX/Vogtlands, 12" brake upgrade
    Modified SSAC headers, K&N Intake, 3.4 MPS, S1X, Gen V, 104's, HPTuned.

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    GrandPrix Junkie stealthee's Avatar
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    Default Re: What tire size do you run on 18" wheels?

    Quote Originally Posted by NegativeOne13 View Post
    I'm running 225/45 on front and 245/40 in back with no issue on 18"x8"
    Why? 225/40/18 is only 25.1" tall and 245/40/18 is only 25.7" tall. Stock is about 26.7" Your speedo is WAY off.
    2007 Pontiac Grand Prix GT - Daily driver. ZZP 3" catted downpipe and intake
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    Pretty colours matt5112's Avatar
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    Default Re: What tire size do you run on 18" wheels?

    245/45r18 or bust....

    Unless you wanna go wider...

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    Default Re: What tire size do you run on 18" wheels?

    if you want to slam your car like a boss you run 215/40/18.

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    GTP Level Member codyAK's Avatar
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    Default Re: What tire size do you run on 18" wheels?

    I'm running 245/45-18 as well, which is perfect in my opinion.
    2001 Pontiac Grand Prix GT : Stock and slow and SOLD.
    2001 Pontiac Grand Prix GTP Special Edition

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    top 5 dead or alive OmegaRed's Avatar
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    Default Re: What tire size do you run on 18" wheels?

    255/45/fatties here

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    GT Level Member 04BlackComp_G's Avatar
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    Default Re: What tire size do you run on 18" wheels?

    245/45/18 is the only size you should run on an 18" tire unless you have a gxp. Not gxp rims but the actual gxp itself.

    Stock wheels rotate 758.2 times per mile.

    245/45/18 757.1

    235/50/18 739.6

    235/40/18 794.6

    Big difference on the sizes. Just based on that you should know what to use. Hope this helps everyone when deciding what size tire to use.
    2009 G8 GT #1311 of 1949: CTS-V front/Camaro rear brakes, Solo Performance axle back exhaust
    2004 GTP Comp G: red prj wires, carbon fiber inferno spoiler, 18" mille miglia ev-s wheels, pioneer-z3 nav

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    Default Re: What tire size do you run on 18" wheels?

    you want to stay within 3% of the stock overall diameter to not throw off your speedo.

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    GTX Level Member Ridin ON Chrome's Avatar
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    Default Re: What tire size do you run on 18" wheels?

    245/45 the correct size.

    I run 245/40s on my GTP since im slammed like a boss.. hahha
    98 GTP-Mods? Yeah, lots of them
    01 Regal GS- DD,but it looks good


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    SE Level Member Jochen's Avatar
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    Default Re: What tire size do you run on 18" wheels?

    Quote Originally Posted by codyAK View Post
    I'm running 245/45-18 as well, which is perfect in my opinion.
    That's what I think.

    Thanks for all comments

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    GT Level Member andremike's Avatar
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    Default Re: What tire size do you run on 18" wheels?

    I found a 18 rim with 255/40 tires. To small? Will it make the speedo to far off? I didn't see anyone mention that size? How will the ride change compared to the 16 stock tires
    Last edited by andremike; 09-22-2011 at 07:40 AM.

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    Default Re: What tire size do you run on 18" wheels?

    those should be fine. they are wider than we normally recommend, so the 40 series probably evens it out for the most part. cant get to any tire size calculators at work...

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    GT Level Member andremike's Avatar
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    Default Re: What tire size do you run on 18" wheels?

    Found a calcultor... it sais 2.2% too fast.. when speedo reads 60 actually going 58.7.. not to bad.... so will1.3" shorter sidewall effect the ride at all.

    How are michelin pilot xgt tires?

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    GrandPrix Junkie stealthee's Avatar
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    Default Re: What tire size do you run on 18" wheels?

    2.2% is a lot when it comes to tires. You should keep it within .3%

    255/40/18 comes out to 26.03" diameter which is .7" too short. Run the correct size and be done with it.
    2007 Pontiac Grand Prix GT - Daily driver. ZZP 3" catted downpipe and intake
    1994 Dodge Stealth - Currently parked. Modded

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    Get off my damn lawn! Bio248's Avatar
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    Default Re: What tire size do you run on 18" wheels?

    2.2% is nothing. 3% is what you want to stay within. 0.3% is nearly imperceptible.

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