# 17" vs 18" mpg



## 04goatgirl (Jan 15, 2005)

Does going from 17" to 18" wheels and tires have any effect on gas mileage? I'm not complaining about mpg like some do, just curious.


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## b_a_betterperson (Feb 16, 2005)

The only conceivable delta would be the difference in the weight of the wheels. Seriously? No real difference. Steelers had a lousy day in camp. Okobi's out -- and his career might be done. :willy:


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## enjracing (Jun 7, 2006)

that's just dumb.


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## Napoleon_Tanerite (Aug 3, 2006)

any possible difference would be neglegible


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## 04goatgirl (Jan 15, 2005)

enjracing said:


> that's just dumb.


Not as dumb as fretting over mpg for upteen threads.


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## UdnUdnGTO (Jan 30, 2006)

MPG, is that mumbles per gallon. Hey I just count the FPG. That is fun per gallon. I am getting around 55 fpg. That is something to talke aboutarty:


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## SJAndrew (Sep 28, 2004)

b_a_betterperson said:


> The only conceivable delta would be the difference in the weight of the wheels.


Not 100% true.

You would have more rotating mass but also a slightly different rolling radius too. The latter would provide slightly different gearing and conceivably better mileage.

That being said, the difference between the two (17" versus 18") I think would be statistically insignificant.


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## Cadsbury (Dec 6, 2005)

depending on the tire size on the wheel, could play a role in MPG's, but nothing to write home about... Looking at a tire size chart, you can come real close to the same overall size of the 17's with 18's.

Chris


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## b_a_betterperson (Feb 16, 2005)

SJAndrew said:


> You would have more rotating mass but also a slightly different rolling radius too. The latter would provide slightly different gearing and conceivably better mileage.


Assuming they'd go +1 from 2454517 to 2454018...


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## b_a_betterperson (Feb 16, 2005)

enjracing said:


> that's just dumb.


That's just rude. We're not that kind of forum. People shouldn't be afraid to ask questions here.


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## 04goatgirl (Jan 15, 2005)

Thanks to all that replied and I thought that was rude also. Like he once said, in his many mpg threads, if you don't like it, don't read it and please don't bother to comment.


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## enjracing (Jun 7, 2006)

allright fine. i'm sorry!!!!!! geez.


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## Cadsbury (Dec 6, 2005)

And your how old? Pretty low on the maturity scale...


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## enjracing (Jun 7, 2006)

blow me, guy. i said sorry. get over it. i still think it's a silly question though.


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## stupidaznmunkey (Apr 22, 2006)

going from 17s to 18s will only lower your acceleration since like the aforementioned, the rotational mass will be more, and your car would need more momentum to get going - but you'll reach a higher top speed.

and since you need more momentum, your car will also use more fuel - but most likely a negligent amount - it wont affect it +/- 1 MPG.

what you SHOULD be concerned about is trying to keep the overall diameter of the tire about the same - since the RPM/MPH gauges are measured in that sense. show us some pix of the car!


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## burnz (Jul 26, 2006)

if the over all size of the wheel is the same, and you go to 18's then the wheel on the 18's will have less rubber and side wall. which will roll easyer because it's stiffer. but:agree it wont be to much different.


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## GTOooo (Feb 5, 2006)

unfortunately the calculator that I knew about which would tell you EXACTLY how much the difference is, is no longer available. The scientific explanation you are looking for is something I can't thoroughly explain very well but it goes something like this. The larger the rim size the less mpg you will get. The larger the tire (the 2nd number in a tire size, ie: 245/*45*/18) the better mpg you get. Sorry I can't be more explicit but I forgot the more detailed response. That pretty much sums up what you are looking for though I believe. So in conclusion 17 inch rims will get a slightly better mpg.


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## jacobyb (Jan 2, 2006)

GTOooo said:


> unfortunately the calculator that I knew about which would tell you EXACTLY how much the difference is, is no longer available. The scientific explanation you are looking for is something I can't thoroughly explain very well but it goes something like this. The larger the rim size the less mpg you will get. The larger the tire (the 2nd number in a tire size, ie: 245/*45*/18) the better mpg you get. Sorry I can't be more explicit but I forgot the more detailed response. That pretty much sums up what you are looking for though I believe. So in conclusion 17 inch rims will get a slightly better mpg.


I don't know where you are getting that, but it is simply not true. Even remotely. Saying that the larger the wheel the less economy, yet larger the tire sidewall, the better the economy is contradicting. If the sidewall is taller, the overall diameter of the tire is larger. So what is the difference between a larger wheel and a shorter tire vs. a taller tire on a smaller wheel?

Rolling diameter is the issue here. If the rolling diameter does not change, then the effort (energy) the engine has to put out to move the vehicle will not change unless there is a significant change in the weight of the wheel.

Just because wheel A is 1" larger than wheel B does not mean that it is going to weigh more. For example, the GTO 17" wheel has a lot of material that is not necessary except for asthetics. This adds weight. Also, the 17" tire is not only wider, but also taller meaning that the rubber is going to weight more.

WIthout the actual weight of each wheel, we can't speculate on the rotational mass. However, we can say that the rolling diameter is identicle between the 18" and 17" wheel meaning that there is not going to be any difference in acceleration, top-speed, MPG, or any other performance related numbers.


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