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Bigger the diameter, the more rotating inertia, the more power it takes to rotate the un-sprung mass, hence the worse MPG you get. There is far more to MPG than just RPM, you could save gas if the tire where really light, but chances are you would spend more on the rims/tires than you will save in gas.

My GS-R can get 40 MPG and cruises at 4,000 RPM at 70 MPH.

 
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I am just temporary in USA, and my native language is not english. The english is my fift language. So I gues is not that bad. Some of you know just english. So don't try to be brave. Spelling mistakes are not that bad that make the mesages unreadable. Sory for you.

 
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Yes I agree with some of the statements. The more rotating inertia is evident in city driming, less in Hwy driving.
Hey guys, put your MPG and tire diameter in the post so we can judge.

 
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You are correct, it is more evident in the city, but without actually knowing the weight of the tire and rim (or actually the moment of interia) the number will not matter much. And I'm guessing very few people actually know the moment of interia of the setup.

Agian like I said, it's possible to get bigger tires, with lower moment of interia, but you are going to spend a bit of money to get the high quality rims like that.

 
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hummm.... yeah I can see that. So what is your native language? You say you know 5, but I'm going to guess you are Indian, because most Indians I know have to learn 3 languages by the time they go college, just a guess though Good job being able to learn so many languages, I personally am only working on my third, grad school is just way to time consuming.

 
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Yes is true.

 
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rotating mass
not unsprung mass. although the wheels are unsprung mass, unsprung mass has nothing to do with mpg because its all the same weight your pulling, its the rotating mass that concerns you because thats what you need to turn to get rolling.
i know you already know this but some wont and you just worded your statement wrong.

 
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Just turned 1100 miles and I check the in town mileage and got 29.78 MPG, close enough to 30 to make me grin because my previous V6 Mustang got 16 in town and 21 on the hwy. I don't drive 'hard' but I don't exactly baby it either. Anxious to check mileage on the hwy and no doubt it will get 40 like it should. Very nice car and we really like the economy and how roomy it is and well built. Not one squeak or rattle and absoultely nothing wrong with it since day one.

 
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Well, I was refering to the rim/tire, brake rotors and all that stuff. You could theoretically save gas by switching to say a Titanium rotor, but I think the cost be a problem But yeah, you're right, we're only talking about the tire/rim here.

 
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thats nice milage

 
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Bukake! I got 42 mpg from Las Vegas to So Cal. Avg speed 75 mph.

 
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i get 19mpg in my civic... the dealer doesnt believe me and they think i race it.. its just runnin way too rich

 
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that sucks...thats always the dealer's way of jipping ppl out of warenties and such.

 
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wow, hahaa; didn't know i'd get 7pages of responses!

 
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anyone got a pic of the gauge needle position after topping off the tank?

 
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No, but I thik that the hond construction is in souch way that even if you topp of the floating sensor will not move higher. then max. You just get more miles than in normal situation before the needle moves. In so toyotas geting beyound the max even you are not topping off.

 
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as mentioned above, the sender unit is attached to the fuel pump assembly which sits at a certain position in the tank, and the sender, when the tank is full, will sit at its highest point. It wont go any higher. Topping off after the tank is already full only will cause other problems. thats why you arent supposed to do it.

 
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most people complain that the epa standards are not up to date but for an 05 lx auto it says 29-38 and that has always beeen true, rigth now ive gone 350 and i need to get gas but im guessing it was about 33-34 mpg, but teh highest ive gotten was like 37 so i dont think people should worry about how accurate they are, if you drive easy it does save a lot, and sometimes its a fluke as well

 
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Today I puled to the gas station to fil up, because the low gas light come up. I had driven 475 mi, and the needle of the gas gauge sowed one mark above empty. I was expecting to put around 11 or 11,5 galons in, but gues...
It came out 13.7 galons. I am mad in situations like that. Puting more than 13.2 galon (the tank capacity) I had one time the same situation but I will never return to that gas station anymore. Now another gas station on the black list.
Any of you folks filed up mor then the tank capacity witout topping off? Posibly they just rob me from $4.

 
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Report them to the weights and measurements department.

I did that once at Sheetz, I put a 5 gallon gas container for my tractor and put 5.2 gallon in it and it still didn't reach the 5 gallon mark.

But you should note that it is possible to put more than 13.2 gallons into your car. The tank it's self is 13.2 gallons, but that does not include the tube that comes from the tank to the point where you fill it. Also there is an activated carbon canister in thatu tube that has between 0.25 and 0.5 gallon capacity. The pump is suppose to chut off before getting that high because gas kills the activated carbon, but sometimes that doesn't happen.

 
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right, well topping off wont cause problems first off.........second off i was asking for a pic because i removed my needles and i think it is off by a little when i put it back.

 
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yes topping off a tank will cause problems. Now it is ok, to top off as in add a few more clicks to get it to a certain dollor amount, but if you top it off till gas sits at the top of the fuel filler, then yuu risk damaging your charcoal canister. I have seen it several times. This is why it says on fuel nozzles
"DO NOT TOP OFF".

as jrfish said, in the fuel filler, it has a passage way to the charcoal canister. When you are driving, fuel vapors are sent to that canister. Now if you continue to top off, you will have fuel sent to that canister, which will saturate it and destroy it.

 
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yea i got that, i thought u meant it was bad to give it another click....thats what i consider topping off. i would never just keep going and going.

 
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I get 19mpg if I am lucky (strictly street).. what gives? 02 civ EX

 
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19mpg. Wow.

When the RPM's get to 3-4000, you want to shift to the next gear. It's not cool to be going down the freeway in first gear

 
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<=-=- Lazy Brooklynite, I have an Automatic

 
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That's good for you, I always get 25-27 in my 240sx since I changed my tires to 245,255. It was like 27-30 before.

 
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Brooklyn... lots of stop and go traffic, always setting in place.... I can easily see why you don't get good MPG.

 
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Did my mpg today and I got a wooping 13 mpg!!! yay lol....I took miles down for 3 weeks and got a percent of 13-14 mpg....and what was very interesting was that the slower and lower my rpm's are I drive on the more gas I waste....my car likes going over the 3k area or else I get less gas milage...I thought that was interesting...
EDIT:Civic and Mustangs have different redlines....when your in fifth gear going 60(?) your hitting 3k rpms..(i think im right) me in fifth gear hitting 3k rpms am going 100+....so theres so dif there...I can be going 20mph at 3k rpms...

 
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well right now i am on my way to 42 mpg i think, i shall see after tomorrow, i am at 325 miles after putting 9.45 gallons of gas in and i have a quarter left