I am wanting to buy some new Chevy wheels (http://i96.photobucket.com/albums/l1...d09/wheels.jpg), but the tires they fit are a bit bigger than the ones I have on now (currently have the stock 255/70r16 chevy wheels for my '01).

Would the 275/50?r20 those wheels come with decrease my mpg by a significant amount?

If so, I'm fairly certain the wheels are only 20x8.5; would it be possible to get narrower tires (closer to the 255) that would still fit the 8.5" wheel?

 

When you change tires size you increase rolling mass which makes the engine work harder to get rolling and the brakes work harder to get stopped. So if you are going from 255/70R16 you need to find a tire calculator to determine how much bigger the 275/50R20s will be.
Here's the one I always use to figure these out:
http://www.discounttire.com/dtcs/infoTireMath.dos

Another thing when you change tire size you can throw off your Speedo.

 

Well according to that, there is barely any difference between the two tires.

My bad has measured the stock tires that he's seen on those wheels though, and they're about two inches taller overall and about two inches wider.

 

If you measure it it will be bigger but what matters is what the rolling circumfrence is not the diameter.

Yeah a 275 is going to be wider than a 255 that is your tread width. Here I'll break it all down for you.
255=Tread width, usually measured in mm(milimeters)
70=aspect ratio of sidewall/ Percentage of total tread width(on a 255/70R16 it would be 70% of 255mm
R= Radial, Not the Rim size
16= Rim size

Okay so given all that a 275/50 is going to be somewhat(not a whole lot) bigger than a 255/70

It still equals more weight having to be moved by your truck. Although because it's such a minor difference it may not hurt your gas mileage that much if at all. It's all going to come down to do you want the wheels bad enough to offset the possible increase in money you'll shell out for gas.

 

My 2004 Silverado had 16" rims from the factory (2wd), but a previous owner replaced them with 17" Chevrolet rims from a 4x4 Silverado. My tire size is now 265/70R17 (Goodyear rubber), and I am sure I get slightly less fuel mileage than I would with the stock rubber.

That being said, I did not buy my Silverado to be an "economy car" - as I already have a Nissan Sentra for that - and the 17" rims look so much better. I have had more than a few folks ask if my truck is a 4x4, as it appears to sit up an inch or two higher.

I will soon be buying four new tires for my truck and am considering the same size tire (obviously), but in Michelin. Costco doesn't carry Goodyear in my truck's size - so it is either Michelin or Bridgestone and I prefer the former. Since I don't "off road" at all, I will get a highway tread with an "all season" rating. Two-wheel-drive trucks are always horrible in snow anyway, so I will use my front-drive Sentra in the event of snow.

If I lose 1 mile per gallon with a slightly larger tire, so be it. Don't sweat the small stuff, eh?

 

I can deal with 1mpg loss (which I am kinda doubting I'd get anyway), but if it was two-three or more, I'd stick with my stock wheels and tire setup :P

Thank you very much for your help, both of you.

 

Hi zm1040,

Welcome to the Chevy Forums.

Even changing to an off-road tread from the standard highway tread will cost you some mileage.

I tried to be slick(turned out I was only greasy) and put the same OEM highway radials on my new custom wheels, thinking it would be the same MPG.

As it turned out, since the new rims offset outwards a couple inches from the original wheel, I wound up losing @1/2MPG or so. But now I have better traction and handling, for which I'm willing to trade a little economy, anyway.

 

less than 2.5 inches would not hurt fuel as much as tire being wider
More weight, and road friction. would be more of a factor\\\\I would goto 235/85/16. taller, narrow low friction.Height helps the look, as much as wide tire
Dimension Tire A: 275/50 R 20
(31 x 10.83 x 20) Tire B: 255/70 R 16
(30 x 10.04 x 16) Difference
Circumference


96.85" (2459.87mm)

94.42" (2398.29mm)

-2.42" (-61.57mm)