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2005 CGM GTO
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1,523 Posts
Discussion Starter #1
If you changed your 17 inch tires and wheels to eighteen inch what effect is that going to have on your gear ratio? I would imagine the stock gears would not be as tall. If so how much lower would the ratio be? Thanks
 

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Gone but not forgotten
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4,672 Posts
it depends on how you do it. if you get 18 rims and tires with a thinner sidewall (lower profile), they should have about the same over all outer diameter. this will have a zero effect on the car. if you call up tirerack.com, one of their sales associaites will be able to reccomend the proper size tire.
 

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Oh my f*ck!
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6,464 Posts
GTOdriver7 said:
it depends on how you do it. if you get 18 rims and tires with a thinner sidewall (lower profile), they should have about the same over all outer diameter. this will have a zero effect on the car. if you call up tirerack.com, one of their sales associaites will be able to reccomend the proper size tire.
Try out this tire size calculator (it's Java based FYI).

Stock tire is 245/45-17, put in whatever other size tire you want, it will tell you how close they are. 245/40-18 (what most people are recommending for 18x8s) is off by 0.1% (slow) from stock, according to that.
 

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May I quote you on that?
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22,046 Posts
My speedo's already too damn fast with the stock tires. Going to 18's added 2/10 MPH error. Can't wait to get an editor.
 

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I hack cars.
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8,111 Posts
Hows your speedo fast with the stock tires? Just overall off or?
 
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