Larger Tires Vs. Fuel Economy

[HDNut]

Just to start off... I'm new to the site and just wanted to let you know you have a great site with great information.

I just bought a 2007 GMC Sierra Z71 Crew Cab,Short Box with the 5.3l v8. So far i like the truck alot but am never satisfied with leaving one stock. My last truck had a 6" lift with 35" tires. I lost alot of towing power and fuel economy and after that and said i was never going that far again. I tow my Jeep from trail ride to trail ride on occasion but for the most part i drive the truck for a dailey driver. I just got in the Rough Country 2" leveling kit and plan to install that tomorrow. The truck currently has 265/70/17 tires and i am considering going to 285/70/17 on my stock wheels. My question is for all you guys that went to the 285/70/17.... How did it affect your fuel economy and did you notice much of a reduction in towing capability?

I'm sure i'll have many more questions for you all as i begin my modifications. Thanks in advance for the info or any advise you have. Thanks Jared

[Zak_LScrew]

Welcome to GMT Jared... I did not have 285/70/17s on my truck but I had 285/65/18s and I would say I lost 1-2 MPG on average. I also have a 2" rough country lift as you do. I think the leveling kit has something to do with mileage as well. There is a wealth of infomation about the subject your asking on this site. Try the search feature by entering key words.

[Stevens03]

Welcome to the site and congrats on the new truck. Larger tires = loss of mileage. You'll most likely see 1-2mpg less if you bump to 285's.

[crenca]

Welcome to the site and congrats on the new truck. Larger tires = loss of mileage. You'll most likely see 1-2mpg less if you bump to 285's.

 

 

 

Not that I doubt it, but what is the reason for this fact?  I would think that if you left diff gearing the same, the higher weight and rolling resistance of larger wheels/tires would be offset by the higher final ratio a taller tire would cause and would be a wash in most driving situations.

[jjohns]

Welcome to the site and congrats on the new truck. Larger tires = loss of mileage. You'll most likely see 1-2mpg less if you bump to 285's.

 

 

 

Not that I doubt it, but what is the reason for this fact? I would think that if you left diff gearing the same, the higher weight and rolling resistance of larger wheels/tires would be offset by the higher final ratio a taller tire would cause and would be a wash in most driving situations.

 

 

 

It has to do with the amount of weight added to your truck and wind resistance. larger tire/wheel combo generally equals more weight. The weight is a factor when you pull out from a stop. Especially a problem in city driving. The wind resistance is not your friend at highway speeds. I am not sure of the physics of how this works, but in general as you raise your truck you create a larger profile. A larger profile equals more wind resistance. So the extra weight causes lower gas mileage in city driving, and the higher profile from your lift causes lower gas mileage during highway driving.

 

 

 

[crenca]

Makes sense JJ04Z71.

 

 

 

 

I wonder how much unsprung weight plays a factor.  We know from our high school physics that it takes more energy to rotate (and stop rotating) a heavy wheel as opposed to a lighter wheel.  This is probably the source of the lower mileage in town as opposed to the additional curb weight of the wheels/tires themselves.

[AdioSS]

Hmm, I've been looking into going back up a little in overall tire diameter recently thinking that the change in gearing might help fuel economy. I never really thought much about the additional weight and the increased ride height until reading this thread.

 

My factory tires were the skinny 245/70R17s and when I put on slightly shorter 275/60s I did notice a reduction in fuel economy. I attributed that to the slight change in gearing, additional width, and probably more importantly, my right foot seemed to get heavier with the stickier tires