Realistic mpg's

Havvkeye · December 22, 2016

If your 305/55 R20 tires replaced an OEM 275/55 R20 then your speedo is 4.1% off and you're screwing yourself out of 1440 miles of a 36,000 mile warranty..

https://tiresize.com/comparison/

I think you are thinking about it backwards. My circumference increased so I am actually traveling further than my car expects (given it's previous calibration as it is done on tire rotations). I am actually getting more real mileage out of my warranty.... but honestly not enough to really matter.

edit: Also note that most vehicles come from the factory reading low in terms of MPH (biased up to 5% low on purpose varying by make/model usually). Moving up in tire size actually makes my speedo more accurate to real speeds and thus probably real distance as well.

Rolling Thunder · December 22, 2016

I think you are thinking about it backwards. My circumference increased so I am actually traveling further than my car expects (given it's previous calibration as it is done on tire rotations). I am actually getting more real mileage out of my warranty.... but honestly not enough to really matter.

edit: Also note that most vehicles come from the factory reading low in terms of MPH (biased up to 5% low on purpose varying by make/model usually). Moving up in tire size actually makes my speedo more accurate to real speeds and thus probably real distance as well.

Hawkeye,

You are correct and it's my blunder. It's just the opposite. And it probably gives GM another excuse for warranty denial, wouldn't you think?

They could say you cheated on the mileage by using larger tires. Might seem far-fetched but with what GM has told owners and the .pdf posted here on the lift kits in another forum that possibility is very real.

Havvkeye · December 22, 2016

Hawkeye,

You are correct and it's my blunder. It's just the opposite. And it probably gives GM another excuse for warranty denial, wouldn't you think?

They could say you cheated on the mileage by using larger tires. Might seem far-fetched but with what GM has told owners and the .pdf posted here on the lift kits in another forum that possibility is very real.

Yeah, I would agree if the speedo was reading inaccurately. Since it really just took the bias out I don't think they would have a case for warranty denial. (edit: If they would let me get a tune without affecting my warranty, which is the only way to calibrate the speedo, I would do that)

Either way I have an extended warranty and probably won't keep the truck until it expires (I'll most likely trade up in a few years).

SouthernSilveradoGuy85 · December 22, 2016

The psi rating on the door jamb is for the factory tire size based on the weight of the vehicle. If you put 10+ psi above that number I bet your ride is quite bouncy. Now if you drive around with an extra 1000 lbs of sand in the bed for winter, it might ride fine.

There are so many variables that change when you change the tires, that you should do as cowpie stated and get the load charts from the tire manufacturer. But if you stick with the same load rating and size that GM put on your truck, there's no reason to go overboard and overinflate your tires. I bet the center of your tread is wearing off.....

Anyway, I average around 20 mpg highway to 17 mpg city.

Actually for me with pis only around 35 it bounced way too much, especially my '14 that I had. Over 45 it didn't bounce but you felt every bump and rattled your teeth. around 42 seemed to be perfect for me when it came to the ride. And like I said, I never had a wear problem. Now if I did over 50 then maybe, but I never put more than 45 cold in them and never had a wear problem. Only wear problem was when I was in my burnout phase and did a lot of burnouts. After that the tire wear was just fine.

Thestepchild · December 30, 2016

Averaging 22.6 over almost 21000 miles since I bought it end of June this year. Yup. 21000 miles in 6 months. Slowing down. Put almost 400,000 on my last Silverado in 6 years.

ROAD TRIP!!!!

Dnt · December 30, 2016

Truck specs? Do you have any pics of the dash display?

1. Year

2. Model CCShort Bed DCStdB etc

3. Engine

4. Trans (6spd or 8spd)

5. Rearend ratio

6. Mods

7. Highway versus City driving percentage average?

I am only getting 20.5 on a 16 CCShortb Denali 6.2 8spd 3.23 with bed cover/Borla catback/CAI with normal driving / long remote starts and over 50% city driving.

Grumpy Bear · December 30, 2016

Bought ours in July 2016. Total fuel used over 17,000 miles yields 24.8 MPG. Best tank 27.64. Worst 22.86.

jimmyboy8301 · December 30, 2016

Truck specs? Do you have any pics of the dash display?

1. Year

2. Model CCShort Bed DCStdB etc

3. Engine

4. Trans (6spd or 8spd)

5. Rearend ratio

6. Mods

7. Highway versus City driving percentage average?

.

-2017

-CCSB

-6.2

-8spd

-3.23

-4.5"Zone, 305/55/20 Toyo AT2, Airaid MIT, exhaust dumped at axle with dynomax bullet

-averaging 13-14 mpg with long remote starts daily and cold weather

Sent from my iPhone using Tapatalk

Rolling Thunder · February 22, 2017

Mileage from a recent Florida trip: Round trip and last leg was at 60 - 63 MPH. No vibration anywhere at sustained speeds of 75 - 77 thru South Carolina and Georgia I95.

TxTruckMan · February 22, 2017

35 is actually low for a full size truck. I had factory Goodyear SRAs on my '14 5.3 and always kept it above 40, usually was between 40 and 45.

Dude, you are full of so much bad and incorrect information. 35 is the correct pressure for these trucks unless you're heavily loaded. GM actually recommends 32 for the 20's and 22's. At 40/45 psi your wheels will feel like they're made of stone. Please stop posting if you don't know what you're talking about.

TxTruckMan · February 22, 2017

Hi All,

Somewhat new member with a new 16 1500 Silverado LT purchased 10/30. I've done searches to try and figure out what I should be getting for mpg's because I'm a little disappointed so far. I get a lot of compliments on the truck and most people follow with " I hear those get great gas mileage". My last truck was an 04 F-150 Lariet 5.4 with 150,000 miles and no overdrive. I was getting around 12.5 mpg's around town. The new truck has 5.3 with 3.74 gears. Stock 20" wheels and no modifications other than cosmetic. The only thing I've done that would affect it is a tonneau cover. A guy at work has same truck except his is a 2015 and he claims +/- 20 mpg's. My numbers according to the dash are....

2155 miles

11.4 average

23.9 best ( all highway)

I've been keeping track with the trip and calculating the old fashioned way for the last 3 fill ups and consistently averaging 14.5 with 75% in town and 25% highway. Honestly I kinda drive like an old lady so pretty sure that is not the problem.

Am I way off or will it get better after the truck breaks in?

Your problem is your short commute. Your truck doesn't have enough time to warm up and will not run at peak efficiency until it is. Your engine runs a little rich (burns more fuel) until it's heated up, and cold fluids don't flow as well. Your results will improve in the warmer months.

TxTruckMan · February 22, 2017

I've also always had trucks with nice sidewalls, none of that low pro crap. So 32-35 psi makes the tires look flat with a big bulge at the bottom. Then imagine putting a decent amount of weight in the bed. I just found having it between 42 and 45 seems to be the sweet spot for me. Gives a good enough ride and doesn't seem low. I've never had the psi go over 48 after driving even in the summer on a long trim and never had wear problems running that range of psi. So ya 35 just seems low to me for a full size truck. It might work on a low profile tire since the sidewall is probably more stiff and doesn't bulge, but just seems like the more sidewall you have on a heavy truck the more psi you can and should run. Even on a passenger rated tire.

That "bulge" is the whole point of having pneumatic tires - to absorb impacts and give a smooth ride. 100 years ago cars had wooden wheels with solid rubber tires - great for longevity but very rough and harsh ride.

Run this test - clean your tires and put Armour All all over the treads. Then go on a short drive on a normal flat road. The AA should wear off evenly across the entire width of the thread. That means that you have an even contact patch. At high pressures, your tires are rounding and bulging in the center instead of being flat across the treads and you will not be using the entire tire. This is unsafe as you are not using the entire contact patch as your tire was designed to be used. Less contact with the road results in less traction. Not to mention that your tires will wear out faster down the middle because you're not using 1/4 to 1/3 of the available tread.

There's actually a science behind tire design and recommended pressures. You're basically throwing it all away and ignoring the experts.

Grumpy Bear · February 28, 2017

Dad's 10% rule has worked for me for a life time. (non-factory tire) Set the pressure. Drive an hour on a dry day on a paved road. Check the pressure. A rise of 10% is the target. Where did Dad get this rule? USA Army circa 1950. Yes car/truck has to have a good alignment. Good shocks etc. If the tire us under inflated the pressure will rise higher as more work in driven into the tire. Under inflated not enough. Tire has to be at correct temperature to get best bite. Correct pressure to get best wear. It doesn't hurt to rotate and balance often and keep that alignment spot on. A good pressure gauge and a depth gauge, your due diligence and bingo. I have little trouble doubling the basic tire warranty tread life expectation.

Your results may/will vary.

njk4o5 · February 28, 2017

100% stock 2014 high country 5.3L

I get 14-16 mpg hand calculated everytime no matter highway or city

Rolling Thunder · February 28, 2017

Dad's 10% rule has worked for me for a life time. (non-factory tire) Set the pressure. Drive an hour on a dry day on a paved road. Check the pressure. A rise of 10% is the target. Where did Dad get this rule? USA Army circa 1950. Yes car/truck has to have a good alignment. Good shocks etc. If the tire us under inflated the pressure will rise higher as more work in driven into the tire. Under inflated not enough. Tire has to be at correct temperature to get best bite. Correct pressure to get best wear. It doesn't hurt to rotate and balance often and keep that alignment spot on. A good pressure gauge and a depth gauge, your due diligence and bingo. I have little trouble doubling the basic tire warranty tread life expectation.

Your results may/will vary.

Grumpy,

I tested just that a few weeks after my delivery last November. The factory / dealer pressures were set 37 / 38 PSI cold on my 20" OEM tires. With two good tire gauges I set pressures to 32 PSI as posted on the door jamb after sitting cold overnight . The TPMS showed very closely to that, actually within 1 PSI which was also part of my testing. I haven't touched my tires since and on a trip to Florida pressures increased after running 70 MPH + to 37 - 38 PSI which is normal. It's a little more than your 10%. Tires have changed a lot since the 1950's.