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puddins betch
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i am thinking about putting 17/18's on my 05 ZX3 i know i will get better performance but i really want to see mor MPG
could any one reply with MPG changes
also what all do i need to look out for
offset
too wide/ tall
spedometer reading low ( have programer allready )
 

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I feel as though the first thing I should point out, on the off chance you werent aware, that larger wheels only help you in handling. They slow down your accel, increase braking distances, increase wear on your brake components, and have the side affect of costing money in and of themselves, as well as typically having tires that cost more and wear faster.

My point is only that you seem to hold MPG in high regard; the cost of a set of 18's, or even 17's, will much more than destroy savings at the pump. I drive around 20k miles/year @ about 30mpg post-SCT tune. At $3.00/gal for premium (its more than that now) thats $2000/yr for gasoline. Another 10% increase in gas mileage, to 33mpg, which would be difficult, would save me $182/yr. Where new set of 04 SVT rims and good tires for them would cost me over $1000 shipped, mounted and balanced, I'm pissing 6 years of saved gas into the wind on a point of aesthetics.

All this said, the stock wheels have a 49mm offset in 7" width (SVT). I believe the consensus was to keep to a 7" rim with as near to 49mm as you can. A brief search pulled up this post, it may be helpful: http://www.focusfanatics.com/forum/showthread.php?s=&threadid=2278

For saving money, nothing will trump A) your driving habits and B) The maintenance state of your car, in that order. Any mod that increases the efficiency of the engine using the same amount of fuel will increase your MPG, if driven the same, but you will see the best increase by driving moderatly when you can, and keeping routine maintenance done on the car. Probably the biggest single efficiency increase after those 2 would be an aftermarket tune.

[/end rant]
 

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You'll definitely see a drop in fuel economy with larger wheels...tires weigh less than wheels, and as you increase your wheel size you add rotating mass while your tires' sidewalls get shorter.

That said, there are other things you can do to offset the loss in economy from larger wheels (assuming you can keep your lead foot under control.) I have 17" SVT EAP wheels and upgraded front brakes (300mm, same as SVT) and I still average 30 MPG on the highway, and about 26-27 in the city (and if anyone wants to call BS, I've been charting my gas mileage for over two years now and have a spreadsheet to back the numbers up.)

In addition to that, I have I/H/E and a 65mm TB which all allow the engine to breathe more freely, which adds up to better fuel economy, assuming you don't mash on the gas all the time. I also have extensive drivetrain mods, the biggest help in fuel economy coming from an aluminum flywheel which nearly offsets the bigger wheels in rotating mass. Granted, if I were to restore my wheels and brakes to stock, and get rid of my 4.06 FD gearset I'd see a boost in fuel economy, but I'm happy with the mileage the car gets now.
 
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