I track my MPG pretty close. I went from stock 17's with stock rubber to 18's with wider and stickier rubber and my MPG went down about 1mpg.

 

A easy way to see the effect in action is to tie a rock to the end of a string and spin it above your head. The shoter the string the easier it is to spin the rock. The longer the string the harder to spin. Same forces in effect with wheel diameter. The overall size is the same, but the weight is farther away from the center point of the wheel making it harder to turn the wheel. Once you get it moving, the force required to keep it moving is pretty minimal. Thats why you wont really see a difference with a lot of highway miles but a larger difference in city/stop and go.

 

^^^^^^^^^
Well put

 

When i had 20"s on my tc i only got about 250 miles to a full tank of gas and my gearing was off the wheels where 23lbs. Now i am running Motegi DP12 17" around 11-13lbs and get around 350 to 375. just my personal expirence smaller lighter wheels are better for MPG

 

Look at the rims and tires of a Toyota prius. They are made tiny to save gas. It's a very stupid looking car. I average 51mpg. While I was moving to my new apartment...and had very heavy loads in the car. My mileage dropped to 46mpg

 

Yeah. . . I only post to clear up misconceptions. . . it's so odd people are so big on intakes that add 1-5hp, yet increase rim size. . . which has about the same negative effect. But people are free to do what they want, I just hope people understand what they are doing

 

the car will handle better w/ bigger rims, and if you add bigger rims and I/H/E you might geta a car with a little more performance however it handles better. What good is power if you cannot control it? And dont forget alot of cars look better w/ bigger rims. I have been told do what you want, its your car. so i tried both i liked the smaller lighter wheels better.

 

OK let me include my 2 cents here. I calculated my gas mileage this last weekend on the trip to exposed. I have 18" Bsa 305's with 215/35/18 tires. I have the GReddy Airinx intake and a catback exhaust. Manual tranny. The entire trip, I ran around 80 MPH. When I stopped in Lexington OHIO to get gas I did a little math, and found that for that tank, I got 34.254 MPG.

 

^^Bigger rims only affect mileage during stop and go driving. Highway mileage wont be affected as keeping the wheels spinning is much easier than getting them started from a stop over and over again.

 

THis is true. . . as the route cause is that bigger rims REDUCE HP and torque (at the wheels). Maintaining speed only envolves the overcoming of frictional forces (and wider rims will affect that, but we are assuming widths are equal).

 

That's not actually true. Wider rims perform better than narrower rims. When people upgrade, they usually get larger rims of wider widths. BUt if you maintain the size and increase width, you increase traction as well. You also have to account for the composition of your tires. OEM econo tires can't compare with high performance tires, which usually come on upgrades. If you upgrade both the rim width and tires, you will be faster than a car of the EXACT same setup, but larger diameter rims. The gains in acceleration and braking are too substantial to warrant the .005G increase in handling. Racing tires (even for smaller diameters) can have stiff sidewalls.

 

Cry me a river!