A real before/after analysis of heavier AT tires w/ level vs. stock

crushNchowda · March 13, 2017

So this topic has been beaten to death a number of times, but I'm going to take as much of a practical/scientific approach to it as I can. I currently have a '15 CC short bed w/ 6.2. 8 speed & 3.23 (or is it 3.42? all terrain package) - I have bilsteins on all 4 corners max height front + an extra 1" in the rear blocks. I have removed the front air dam - all in over the course of ownership about 28000 miles w/ this setup I've averaged 16.2 give or take

I am swapping out my stock 20" wheels w/ 275/55R20 Michelin snow tires & mounting my aftermarket 20" granite alloys wheels (about 5-7 lbs lighter than stock) wrapped in BFG K02's in 275/60R20 size approximately 53-54.5 lbs depending where you pull your info.

So I'm going to weigh both wheel/tire setups (the michelin snow tires are listed as similar/same weight as wrangler SRA's about 40-42 lbs) - use my body as a "tare" & weigh myself holding wheel - not precise/official but if I'm weighing both setups same day same time the delta between the 2 should be fairly accurate....I'm more interested in the difference between the 2 setups than what I come up w/ as an actual weight for each since I'm sure the scale isn't 100% accurate - that being said preliminary test shows my new 275/60r20 BFG's on the 20x9" Granite alloy wheels come out to 90-91 lbs a piece....which I think will result in a 8-9 lb gain per corner. I will update the thread w/ the exact difference in increased weight once I re-weigh the stockers.

After that I will monitor my MPG over the next few weeks w/ the heavier BFG's on the stock tune.

I am then having a custom dyno tune performed to help alleviate the speedo inaccuracy along w/ smoothing shifting & hopefully offsetting some of the impending drop in MPG's I will experience w/ the heavier rubber.

Attached is a pic of the new setup - looks awesome. The center caps of these wheels were rough - paint flaking off & the "granite alloy" decal sticker fell off 1 of them - so I opted to have them powdercoated flat black before putting everything back together. Also got some nice Mcgard black lugnuts to complete the look.

Will ultimately have an idea of MPG before the tires on stock tune w/ splitter removed & lifted 2", an MPG avg w/ the lift & heavier BFG's stock tune, & a final MPG range w/ a tune added see if I can gain any mpg back.

My best guess is I lose 1 mpg overall - due to the relatively tame tire size/weight & the lighter aftermarket rims the 90ish lb total is nearly identical to a stock 22" wheel setup like the Denali, which yields similar mpg to any other of GM's trucks despite the extra weight I'm guessing the lower rolling resistance helps in that scenario though & that is ultimately what I think will hurt my setup despite the relatively modest overall weight increase.

Doobs41378 · March 13, 2017

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Ezekiel2517 · March 13, 2017

I have a similar setup with bilsteins on the 3rd notch and P275/60/r20 Terra grapplers on stock wheels. The Nittos are much lighter than the BFGs. Left front valance on. Have soft tonneau (which does nothing measurable for MPG). So I am not quite as tall, not quite as heavy tire, and still have valance.

In town, I do about the same MPG as before. 15-16 mpg. Not bad, I think.

On flat highway at 70mph, with no wind at all I can do about 20mpg, after correcting for 3% diameter change. This is pretty close to what I did before, definitely within 1 mpg. Still pretty good. Where I notice the biggest effect is if I am driving in wind. headwind or crosswind kill it. The taller truck and larger tire do about 2 mpg worse than before the lift and tires.

Not scientific, but observed several times over the last six months.

Havvkeye · March 13, 2017

With my tires and a 2" front level I lost about 4-5mpg.

Sierra706 · March 13, 2017

With my tires and a 2" front level I lost about 4-5mpg.

With or without adjusting your speedo?

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Havvkeye · March 13, 2017

With or without adjusting your speedo?

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Without adjustment so less than 4-5 in reality, but still more than 1-2. I didn't adjust because now I am running close to true instead of padded as it comes from the factory.

Sean Neilan · March 13, 2017

Without adjustment so less than 4-5 in reality, but still more than 1-2. I didn't adjust because now I am running close to true instead of padded as it comes from the factory.

The speedo isn't "padded" fast from the factory and when you add bigger tires your speedo shows even slower, so all you're doing is increasing the "padding". Whereas stock maybe it showed 70 but you're really doing 68, when you add bigger tires you'll show 70 but really be doing 65

RHStansbury · March 14, 2017

In for details. I am seriously considering just picking up a set of 275/60 KOs and throwing them on without a leveling kit.

Havvkeye · March 14, 2017

The speedo isn't "padded" fast from the factory and when you add bigger tires your speedo shows even slower, so all you're doing is increasing the "padding". Whereas stock maybe it showed 70 but you're really doing 68, when you add bigger tires you'll show 70 but really be doing 65

The speedo most definitely is "padded" from the factory, usually anywhere from 2-5% depending on manufacturer.

You're telling me that if I increase the diameter of my tire I will cover less ground with the same number of revolutions of the tire? I think you're a little backwards on this one. I am reducing the padding by making my speedo show 70 when I am doing 70 instead of showing 72 or 73 when I am doing 70.

edit: or with your number stock maybe it showed 70 but you're really doing 68, when you add bigger tires you'll show 70 but really be doing 70

crushNchowda · March 14, 2017

With my tires and a 2" front level I lost about 4-5mpg.

Dude - that sounds like something is wrong lol, no WAY you lose that much. What do you think guys w/ "real" lifts (I'm talking 6"+, 36"+ tires - 120 lbs a corner min) lose??? If you're going from a factory stated avg of 17 mixed to 12-13 mpg w/ a tiny level & some pseudo LT tires (I think those Nitto XL's weigh in less than the BFG's like 49 lbs) what happens when you go big? You have to tow an extra gas tank behind ya?? LOL

1-2 sounds more accurate. You should get it tuned.

RHStansbury - these tires should fit on factory wheels @ factory height w/o rubbing.....if they do happen to rub I would imagine it'd be just on the felt liner.

Sierra706 · March 14, 2017

Speedo being off 3+mph at highway speeds could have a 1-2mpg additional penalty. Don't crucify me it's late and I haven't done the math but If someone would like to crunch some numbers please do

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Havvkeye · March 14, 2017

Dude - that sounds like something is wrong lol, no WAY you lose that much. What do you think guys w/ "real" lifts (I'm talking 6"+, 36"+ tires - 120 lbs a corner min) lose??? If you're going from a factory stated avg of 17 mixed to 12-13 mpg w/ a tiny level & some pseudo LT tires (I think those Nitto XL's weigh in less than the BFG's like 49 lbs) what happens when you go big? You have to tow an extra gas tank behind ya?? LOL

1-2 sounds more accurate. You should get it tuned.

RHStansbury - these tires should fit on factory wheels @ factory height w/o rubbing.....if they do happen to rub I would imagine it'd be just on the felt liner.

I feel like there is some reading comprehension that is not working. My description does not say XL anywhere. I have the true LT version of the tire. I did not get my speedo calibrated so it is probably less than 4 but definitely more than 2. Nothing wrong with the truck, just adding that much rolling weight takes a toll on the mileage.

edit: and to answer your question with a 6" lift and 36" (that is a big tire) I would be surprised if the mileage was even in the double digits.

tnchevy · March 14, 2017

I have quite a bit of real world experience when it comes to heavier tires and the result on mpg's. My companies trucks are the lowest bid and usually come with the smallest street or joke of an AT tire that you can get. We usually put on a size or two bigger LT AT tires as soon as possible. I have done this numerous times over the years and it is usually about a 2.5 mpg loss and that is with a corrected speedo. My current company truck is a 2012 F150 with a 5.0 and a 3.73 rear gear. It came with 235/75-17 hankook "AT" tires in a P rating that weighed 30lbs a piece. I rode on those for about 6 months and averaged 20.0 mpg. I then went to a Goodyear Silent Armour LT 265/70-17 that weighs 52 lbs a piece and rarely do better than 17 mpg's and that is with the speedo corrected. Of course this is a much bigger and heavier tire than what came from the factory with an aggressive tread. For tires that are the same size you don't lose as much. On my 2002 silvy I lost 1 mpg when going to a heavier and more aggressive AT tire on the same size tire. There is so much at play because heavier = less mpg, aggressive tread = less mpg, and a level will also play into that as well.

chris15706 · March 14, 2017

Padding from the factory??? My 2017 Silverado is on stock tires right now and my speedo matches GPS. So did the truck I bought back in 2008 when it was brand new.

Sierra706 · March 14, 2017

Padding from the factory??? My 2017 Silverado is on stock tires right now and my speedo matches GPS. So did the truck I bought back in 2008 when it was brand new.

I believe they mean the MPG reported by the truck.

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