Originally Posted by 03sierraslt

Thank's for typing all that so I didnt have too... haha. Case in point, my 20's with tires are the same diameter as my factory 17" wheel and tires setup. However my 20's are a decent amount heavier, Chrome 20's vs. Alum. 17's. With the 20's on I get about 1.5mpg less give or take, I also notice a slight diff. in accel and decel but only when WO or under hard braking. So why do I run the 20's then you may ask... I think they look purdy.

Originally Posted by RandomHero

Dude you are throwing out all this technical jargon and it means absolutely NOTHING.

"My friend got 21 mpg and I get 23 with 20's so it must be true"
Do you realize how stupid you sound.

first of all 20" rims(on the average unless using billet) are much heavier than a stock 16/17" rims.

Secondly, like said, the rotating mass is pushed further out.

Third, you have no idea what you're talking about.

Physics doesn't lie. Hell if you want to throw out the "Objects in motion will remain in motion unless acted on by an opposing force" bull **** then I'll remind you that we all drive a 5000 lbs brick that is about as aerodynamic as Rosie O'donell
Here is what is going to play a factor in your gas mileage:

RPMS- Obviously if you spend time at WOT throttle you'll get terrible gas mileage, however, go too low and you'll be constantly downshifting on hills.

Speed-While related to rpms there is also another factor to take into account....the law of diminishing returns. you may get 15 mpg going 50 mpg and 20 mpg going 70 mph but you won't get 25 mpg going 90 due to aerodynamics and the higher rpms the engine will be turning.

What you're driving-we're driving a truck, it isn't a ford gt or a ferrari, there are very little aerodynamic features that silverado's have.

Rotating mass of the wheels-I have experience on this both from personal experience and from a scientific approach. Having the rotating mass be pushed out further allows outside forces to play a factor in how easy the wheels turn. The further out the rotating mass is taken the more momentum,leverage,etc play a factor.


Anybody can throw out useless terms and then follow it up with "well my buddy got 25 mpg once with his 22's." When you say something like that you lose all your creditability.

Originally Posted by Freakenhye

First of all . Unless you realize that its miles per gallon, and not average miles per gallon, if we are talking about average miles per gallon whitch includes uphill climes, with downshifting involved then yes then you are right. Becuase your whole idea of downshifting on hills cannot be applied to this conversation, being that everyone knows smaller rims and tires are good for acceleration, this is why you dont see 20" rims with slicks on it, but Im talking about crusing at 65mph, and a truck with 20" rims will get more mpg then a truck with 17's, and yes we both tested each others trucks. That has nothing to do with the fact the he saw less, but since you wont be happy untill same driver and same techniques are used then i will do the fallowing.


I just called up my brother and requested 2 silverados to put an end to this conversation we are having, I have gotten hold of a 2 x 2007 silverados 5.3L Extra Cabs both with AFM, both with 3.73's, one with 20's and the otherone with 17's, i will do my testing hopefully this weekend.


Testing will go as fallows.


2 mile run down a freeway at 65 mph on cruise control,

i will get the truck up to speed hit cruise control and drive for 2 miles. then record the findings.

If im wrong i will apologize.

Originally Posted by 1ORANGEWS6

Man I think you are really missing the point. We are not talking about acceleration here for smaller wheels and tires. We are talking about heavier rotating mass. My STOCK wheel/tire combo is the SAME diameter as the 20" wheel/tire combo. The only difference is the 20's weigh more. I'm no scientist but it takes more power to move a heavier rotating mass therefore using more fuel. I lighter rotating mass will take less power to move therefore better MPG.

Also everyone uses AVG MPG to calculate their fuel mileage to take into account of their various types of driving on a tank of gas.

Originally Posted by Freakenhye

... But at speed which lets say is 65mph on long trips a 20 inch rim will get more mpg then a 17 inch rim.

Originally Posted by SnakeOiler

If the tire diameter is greater with the 20's than the tire diameter on the 17's, then I would agree with your statement.

Do not confuse rim diameter and tire diameter. You can run different rim sizes and still maintain the same tire diameter.


Now, as for my truck, I have never seen any change in mpg with any of the mods I have done, and I am religious about keeping track of it.

Though, I have seen changes in my mileage based on the way I drive it.

Originally Posted by Freakenhye

Ok no one was talking about accelration. im gonna do a cruise at 65 for 2 miles, have you tried to push a car and once you got it to move you can keep it moving with little effort.

its the acceleration of the weight that eats up the gas. But at speed which lets say is 65mph on long trips a 20 inch rim will get more mpg then a 17 inch rim.


Once again if im wrong then i will admit it.

Originally Posted by Freakenhye

First of all . Unless you realize that its miles per gallon, and not average miles per gallon, if we are talking about average miles per gallon whitch includes uphill climes, with downshifting involved then yes then you are right. Becuase your whole idea of downshifting on hills cannot be applied to this conversation, being that everyone knows smaller rims and tires are good for acceleration,