what are you guys getting for mpg?

[Otsa580]

My 2010 Silverado ext cab 5.3 4x4 with 3.42's averaged 18 mpg at 75 mph on a 600 mile trip. In town which is 60/40 highway driving I average 15. I do not drive with a light foot because of hills and traffic. The truck has 5000 miles so she is hardly broken in.

I seem to get over 20 mpg at 60-65 but have yet to take the highway on a long trip.

[HEI451]

The whole mileage game is linked to air/fuel ratios, and engine performance packages.

That said, with a cruise air/fuel ratio of say, 14.5:1, 60 mph would use LESS air/fuel flow than 75 mph. Any engine that uses less air to run, such as those with smaller displacements and air flow passages in the head, such as Honda, will get better mileage than other engines that are larger and have larger air flow passages, such as the old 153 Nova inline 4 cylinder.

One deviation to this rule is carburetor vs EFI systems. A carburetor relies on air flow past set orifii to pull the fuel into the engine, and that fuel is in the form of somewhat large rain droplets. EFI, on the other hand, uses pressure technology, which injects a more precise volume of fuel, doesn't rely on vacuum as the carb does, and the fuel is injected as a very fine "London fog" of a vapor.

So, smaller displacement, lower total air flow, more finite handing of the fuel/air mixture and fuel in a vapor form, over a giant rain drop = better volumetric efficiency, better mileage.

[drew86]

I think there is something to be said in the difference in weight of wheel and tire combos also.I even experienced a slight loss in mpg's going from factory 17's to factory 20's.I also had a set of 20x10 kmc's with 305/50's for about 3 years on my 07,and they were definitely the worst.I thought they would be better with the taller tire.My truck is 2wd with the 5.3 and 3.73 gear.Averaged 13.5 with the kmc's,15.2 with factory 20's,and 16 with the 17's.

[piecesparts]

Originally Posted by drew86

I think there is something to be said in the difference in weight of wheel and tire combos also.I even experienced a slight loss in mpg's going from factory 17's to factory 20's.I also had a set of 20x10 kmc's with 305/50's for about 3 years on my 07,and they were definitely the worst.I thought they would be better with the taller tire.My truck is 2wd with the 5.3 and 3.73 gear.Averaged 13.5 with the kmc's,15.2 with factory 20's,and 16 with the 17's.

I would say that for the most part the difference would not be the rolling weight, but the diameter of the tire. The amount of power that is needed to roll a 32" tire is more than what would be needed to roll a 28" or 29" tire. My new truck had factory 32" tires and now I have 30.4" tires on it. It did make a difference to the acceleration, not to mention the wheel well clearance.

[rpmerf]

1970 c20 custom camper 350 8:1 compression, slightly more aggressive cam, 3 speed 4.56 rear 235/85R16 tires

I only measured it once, but I also was leaking gas out of the gas cap so I don't know how accurate it is. It was all highway, mostly around 65, but a few times I found myself doing 75 and a few times I took it up over 90. I got about 12mpg.

A/F ratios are very important, so I plan to install a set of A/F ratio gauges one day to get it tuned in as precise as a carb from the 70's can be tuned. Another big factor that problems almost all cars is fuel atomization. Liquid fuel does not burn, only atomized fuel. There are alot of crazy ideas out there like putting a screen below your carb or tapping the intake ports to help swirl the A/F mixture better.

[KMK454]

With those MPG numbers, they may as well have nixed the 5.3 with DOD and gone for the old 5.7 or 6.0 mill with more horsepower and torque. At the end of the day, it's a two and a half ton brick designed to do work; cutting power for tenths of an MPG isn't worth it, and while there are cost savings to be had, the truck has to be driven tens of thousands of miles over the course of many years to see worthwhile savings from going with a 5.3 over a 5.7 or 6.0.

[piecesparts]

I can say that the 5.3 that I now have is stronger and has more roadability than the 91 that I sold, when I bought the 2011. The computer tune may have something to do with that. It is a strong engine and the acceleration is much better. The gain in gas mileage from the 91 is not so noticeable, but the performance is.

[LEEVON]

I surmise that we can thank federal regulation for the DOD's, AFM's and other do-nothing addons. Enjoy it while you can though, 54.5 mpg by 2025!

[73CheyenneSuper20]

My DIC is reading an overall average of 11.5mpg's...
2008 6.0, 4 speed trans (4L70E), 3.73 gears, 4x4, 5'9" bed, extended cab, 20" aluminum rims, 35x12.50 Toyo's, Cat-back Magna Flow exhaust 1 into 2 duals out the back, some air intake like K&N, and a Hypertech programmer, 85k miles.

I didn't do any of this stuff, I bought it like this in Jan with just under 76k on it. I haven't did the mpg's on paper, but roughly from fillup to fillup it's about right (fillup with about 20 gallons, went about 220 miles, etc)

The Hypertech re-adjusts for the tire size and corrects the speedometer... I think I'm gonna plug it in and see what it says about the program it's running...

[willinwtx]

my 2011 rclb with the 5.3 and 6 speed and 3.42 averages 15.5-16 has 20k on it. it's an oil field truck and 70 percent of my driving is dirt road under 40 mph. my 08 with the v6 and 3.73's averaged 14 the entire 175000 miles i had it.

[Bad70sbchevy]

My 2010 Silverado 4.3V6 with 3.23 gears gets 18.5mpg mixed between rush hour traffic and highway, I ain't complaining.

BTW if you really want better gas mileage you would have to run leaner fuel ratios (that the engine would allow), but you can't pass emissions. I'd have to disagree with carbs getting worse fuel mileage than FI due to them generating a larger dropplet. If tuned right ideally, a carb could achieve the same fuel mileage, but with EFI it is much easier to tailor an ideal fuel curve than a carb and you can get feedback from O2 sensor.

[OLDIRON69]

05, 2500HD 6.0 4.10 gears, last 7.5 hour road trip at speeds of 75-85 I actually got 12.5 mpg! I have never babied the truck and it has 175K miles. The best I got ever was 16 hwy doing 65 the entire way on a very flat road witht he cruise set. When I replace it I plan on a custom tune.

[tonyscustomrides]

i bought a 2011 gmc sierra, rcsb, 2wd, 5.3 AFM Flex Fuel,6 sp, 3.42, all stock and im gettin 22mpg averaging 50mph (back roads). This is no lie, i barely believe it myself. I havent driven it on the highway much, ive had it for two months and just rolled over 1500 miles.

[Chrislidgett]

I just hit 10000 miles on my 11 crew 4x4 I had fast motorsports tune it with 600 miles on it and I average 17.2 mpg back and forth to work hwy/city mix on the 3 hr trip to my parents house I will get about 21
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[stroker87]

Originally Posted by drew86

I think there is something to be said in the difference in weight of wheel and tire combos also.I even experienced a slight loss in mpg's going from factory 17's to factory 20's.I also had a set of 20x10 kmc's with 305/50's for about 3 years on my 07,and they were definitely the worst.I thought they would be better with the taller tire.My truck is 2wd with the 5.3 and 3.73 gear.Averaged 13.5 with the kmc's,15.2 with factory 20's,and 16 with the 17's.

+1

truck with rims lager then 17" will get lower MPG, my 07 suburban with the stock 17's on the Hwy gets 18.5mpg running 70/75mph with my 22" rims same speeds same trip (Chicago to Cleveland) only get 16mpg, mix city/hwy avg 12.5mpg but i have a heavy foot and any time i'm on the e-way i'm driving over 80mph

now I have a programer that I put in economy when taking a trip and can get 17.5mpg with my 22" wheels but it really kills the performance of the suburban and makes it feel like a V6

as for the AFM its a joke only time it gos in to v4 is down hill or when i lift my foot off the go peddle to stop

[piecesparts]

It is not the fact that the rims are larger in diameter. It is the taller tire and the affect that it has on the RPMS and the power needed to make it move. If you go 20" rims, but the tire is approximately the same diameter,then the RPMS will be the same and the MPG will be the same. I am getting decent mileage with my 265/50/20 tires on my new truck, just because it works well with my gear ratio. Plan your change and align gears and tires effectively.

[stroker87]

Originally Posted by piecesparts

It is not the fact that the rims are larger in diameter.

your right its the WEIGHT difference pick up a stock 17" wheel then a 22" wheel you'll see what i'm talking about I've had a few set of rims (8 and counting) on my suburban and most was the same over all tire height so the speedometer would ready correctly but the weight of the bigger or even just a different wheel that weights more in the same size is what kills mpg

my stock tire size is 265/70/17= 31.7 Overall Diameter

my aftermarket wheels have 305/40/22= 31.6 Overall Diameter but weight a lot more then the stock rim/tire combo so mpg suffers

the more they weight the more power it takes to turn them even if they are the same size

if you typed your current tire size correctly you should be getting better MPG that size 265/50/20 is a 30.6 Overall Diameter witch is smaller then the stock 20 inch size that is 275/55/20 and that is a 31.8 Overall Diameter tire

[piecesparts]

Originally Posted by stroker87

your right its the WEIGHT difference pick up a stock 17" wheel then a 22" wheel you'll see what i'm talking about I've had a few set of rims (8 and counting) on my suburban and most was the same over all tire height so the speedometer would ready correctly but the weight of the bigger or even just a different wheel that weights more in the same size is what kills mpg

my stock tire size is 265/70/17= 31.7 Overall Diameter

my aftermarket wheels have 305/40/22= 31.6 Overall Diameter but weight a lot more then the stock rim/tire combo so mpg suffers

the more they weight the more power it takes to turn them even if they are the same size

if you typed your current tire size correctly you should be getting better MPG that size 265/50/20 is a 30.6 Overall Diameter witch is smaller then the stock 20 inch size that is 275/55/20 and that is a 31.8 Overall Diameter tire

Remember the wheel and tire are rolling weight and so with that in mind, there is only a small portion of it that is actully suspended and adding weight to the vehicle. It is not the weight that you are dealing with as much as it is the circumference that you have to get the wheel to turn effectively to make it work. Turning a small gear is easier than turning a larger gear with the same output ratio from the tranny. That is why drag racers go for the different lower gears for different length tracks

You are right, my tire diameter is smaller than the monsters that were on the truck when it was stock. That smaller diameter along with my 3.42 gearing makes the application of torque to the ground much easier, since the smaller diameter essentially changes the gear ratio to a lower gear.

[stroker87]

Originally Posted by piecesparts

Remember the wheel and tire are rolling weight and so with that in mind, there is only a small portion of it that is actully suspended and adding weight to the vehicle. It is not the weight that you are dealing with as much as it is the circumference that you have to get the wheel to turn effectively to make it work.

if that was true why is it that with my 22" rims witch is just a touch smaller Overall Diameter then my stock 17" rims I loose 2.5mpg??

driving the same trip cruise set at the same speeds??? I run from Chicago IL. to Cleavland OH. on business a lot I have made the run many times on my stock rims and on my big rims with my stock rims I get about 65 mile more to a tank

Sorry for the hijack, every one

[maxh]

Well my 07 nnbs cc 2wd did wicked this past weekend. Driving flat with cruise set I got 26mpg at 145k or 90mph in 4 cyl mode. Kickin it to V8 I was getting atleast 22mpg at that speed.

[piecesparts]

Originally Posted by stroker87

if that was true why is it that with my 22" rims witch is just a touch smaller Overall Diameter then my stock 17" rims I loose 2.5mpg??

driving the same trip cruise set at the same speeds??? I run from Chicago IL. to Cleavland OH. on business a lot I have made the run many times on my stock rims and on my big rims with my stock rims I get about 65 mile more to a tank

Sorry for the hijack, every one

What is your gear ratio, tranny type, and what are the two different tire sizes that you are running? If you put your engine at a point where it is now running at an RPM that is just out of the band on the opposite end, it works the other way.

[Bad70sbchevy]

Originally Posted by stroker87

if that was true why is it that with my 22" rims witch is just a touch smaller Overall Diameter then my stock 17" rims I loose 2.5mpg??

driving the same trip cruise set at the same speeds??? I run from Chicago IL. to Cleavland OH. on business a lot I have made the run many times on my stock rims and on my big rims with my stock rims I get about 65 mile more to a tank

Sorry for the hijack, every one

It's probably resulting from a higher rotating mass from the 22" wheels. It takes more power to turn a heavier tire than a lighter one. Either that or a smaller OD is causing the motor to turn more rpms at 65 which can also cause a dip in mpg depending on how much of a difference in OD.

[FMBL]

07 yukon 5.3 auto 3.42's with 305/45-22 seems to get 12.5-14.5 city, hwy or combined.

[swb85]

Even with identical overall tire diameters, heavier rims (ie, higher mass) will absolutely hurt fuel economy, along with acceleration and braking. Look up Newton's law of motion if you're having trouble wrapping your head around it.

[cadpwrd]

Last weekend I took a trip to Canton, OH (with a pitstop at Summit Racing in Tallmadge). It was about a 3 hour drive from where I live in western NY. My 2wd RCSB with the 4.3 averaged 19.6mpg with the cruise set at 73mph. That's the best Ive seen on the highway. I usually average 13/14 mpg around town and 17/18 on the highway.