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Old 05-24-2013, 10:49 PM   #1
metrognome
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MPG of performance tires

Hi. noob here......

I was wondering how much difference there would be, in miles/gallon, running stock size P215/65R/15 and a 215/45R/17 ?

I'm driving an '07 2.0, 5spd, with cruise and NOT a lead foot haha.

Currently get 27-30mpg with the 17's that were on when I bought my Focus.
Would like to get at least mid 30's.

Could I get 5mpg more with a lower friction touring tire?

btw my Focus came into my possesion with a Steeda cai and a cat-back exhaust (that has a very mellow PURR at 70) already.
tia



Last edited by metrognome; 05-24-2013 at 10:54 PM. Reason: added a btw
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Old 05-24-2013, 11:27 PM   #2
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Moved to "Wheels, Tires, Brakes & Suspension" since your question is concerned about differences in tires.
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Old 05-24-2013, 11:49 PM   #3
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First off your replacement tire is way off size. The 215/65/15 is about 800 revolutions per mile. the 215/45/17 is way more revs per mile at around 844.
Your speedo will be crazy off.
If you go for 17" wheels to keep the speedo the same you would need 225/50/17

You want 5mpg more with just tires? crazy.
Well 5mpg more could be had with thin smooth wheels (which is just the opposite of what you are going with bigger wheels, mainy because bigger wheels are wider, and way harder to find skinny tires for..) , that is a wheel cover perfectly smooth either flat or dished, try the skinniest tires you can buy which have long tread full cuircumference with a reasonable on your smooth faced wheels.
Run those tires at 50psi...
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Old 05-24-2013, 11:58 PM   #4
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I doubt he would be ever able to fit that size tire, I imagine you can get some low rolling restance tires, or by going to a 15" or 16" wheel and tire pacakage and get some unsprung mass off the car
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Old 05-25-2013, 04:22 AM   #5
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you would see an increase with LRR tires. but i would only reasonably expect ~2mpg.

if efficiency really is your cause, i would go with a 185 wide tire (narrowest reasonable width) on an aluminum OEM 15x6 wheel.
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Old 05-25-2013, 01:13 PM   #6
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your stock size is 195/60/15 on a 2007 foci
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Old 05-25-2013, 01:26 PM   #7
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Buickboy, I stand corrected. Thank you.
The question remains...( in spite of my miss quoting size)..could I get 5mpg more by switching to the 'stock' sizes?

thanks again

and btw, I do know about tire contact patch size and how it effects mileage but was seeking first hand knowledge from somebody who has changed from one to the other and actually measured the difference.
Real world experience numbers.
I do appreciate y'alls responses so far.

My curiosity arises from the desire to drive 1500 miles one way to visit my daughter and her family.
And what with gas prices being what they are, along with the extra carbon I would leave in my wake, would I truly benefit
5'ish mpg (or more) by changing from the wide 17's to a narrower 15?

btw, I DO like how the 17's feel on the twisties lol
If I could only realize 2-3 mpg I'll stick with the 17's

My last car was a 4 cyl, 5 spd, Suzuki Swift that got 39-42mpg depending on winter or summer gas.
Guess I got a little spoiled and by that 'sipper' and was expecting low to mid 30's from my newly purchased Focus.

I love her.
I just wish she didn't drink so much......
lol
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Old 05-25-2013, 01:57 PM   #8
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Smaller diameter tires will negatively effect MPG, but I doubt you'd see 5 mpg increases going to the different size.

Expect another couple mpg out of it, especially if you get LRR tires.

It should also be noted that the money spent on new tires will NOT be recouped by fuel savings, you will be losing money. If you need tires anyways then great...if not, don't bother. You're just wasting money.
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Old 05-25-2013, 05:49 PM   #9
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I actually disagree. There can be a huge mpg gap strictly from OEM wheel/tire packages. Apples to Oranges here, but in the Mk3 community mileage from the 18's is usually 35-37 highway and those with 16's have seen 45+. Yes there's a million variables at stake, but the point is the same.

I'm under the assumption that you're considering an entire wheel/tire swap due to the different wheel measurements of your quoted tires. Something to consider-under the assumption that Buickboy is correct on the OEM sizing-is that you're already running an oversize tire and as such your mileage is probably currently incorrect by 1.65%.

Are the wheels that are on your car aftermarket? If so, chances are that they are comparatively light for their size. That isn't always true, but realistically it matters for mpg's and would need to be taken into consideration. It is most likely still heavier than the 15's, and the additional rotational mass and it's distance from the center of the axle isn't beneficial.

Joeywhat's final statement is pretty close to correct. If you're trying to get 5-8 mpg by purchasing new 15" wheels/tires, you're probably going to find the math more beneficial by keeping your current set on, unless you plan on running the car for more than one set of tires...
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Old 05-25-2013, 07:14 PM   #10
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That ^^^^^^^^^^plus, a Suzuki swift is a lighter car. The cost of wheels & tires & how long the pay back is. Just to add, the 17's would stop faster & manuver a lot better then the 15's. It could possibley save you from teepeeing your hood= a accedent.
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