Can this be true? Mileage hit sticking with OEM size on BFG KO3's

[JohngaltinOC]

I spent some time looking through here about sizing up tire and what would fit without level, lift, cutting, etc. Ultimately decided to stick w/ 275/60r20 factory size so I didn't have to worry about the above & recalc odometer/speed, could keep original spare, mileage hit, etc., etc.

Online I found Pirelli Scorpion weighed ~49 lbs., and that BFG tire is like 57 lbs with D rated tire (with limited payload number why worry about E rated?).

I was shocked by recent road trip 250 miles (flat + hills) that used to get me 22 mpg at 75+- mph., now it's showing 17 mpg?? I see people talking here about slightly larger tire only taking 2-3 mpg, and I stuck with OEM size. What could be going on here? Can that weight difference really be so dramatic? Why do others see such a small change? Their tire weight had to go up as well...

(Today on Chat I find that the OEM Pirelli's are actually lighter than buying same Pirelli's after market. Who would have thought that was a thing?)

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[jkosh22]

What’s your tire pressures? Higher tires pressures = a little better economy. 17 mpgs sound like real life efficiency to me.

That does seem rather dramatic. Did the weather change? Do you have winter fuel. How far apart were your tests? Many things can affect fuel mileage. Especially gaining 32 pounds of extra rolling rotational force.

 

[Old Hat]

It's not just weight but rolling resistance. Factory tires are chosen for best ride and economy. KO's are the opposite of that. That said, there's something else giving you 5 mpg drop on one trip. Probably wind conditions. You'll need many more miles for a proper comparison.

 

[Flatus]

Those heavy tires definitely make a difference. I have stock size Duratrac RT's in SL. I got 18.4 mpg on a road trip a couple of weeks ago. I had a packed bed and a boat hooked up. I was only running 65-70 mph though.

 

[FaaWrenchBndr]

Heavier tires
Greater road friction due to tread
These heavy big impact
What is your tire pressure is currently

 

[CptBligh]

New tires are 15% heavier, more rolling resistance, less aerodynamic with the aggressive sidewalls. Doubt you were getting 22mpg at 75+ either, maybe 65. Drag increases with the square of speed.

A taller tire reduces gearing so that may balance out somewhat on the highway. I have 275/65/20s and have a lifetime average of 19.4mpg but I rarely drive on the interstate.

 

[ATLalien]

Your OEM Scorpion, may have been lighter than you calculated as well. Tirerack shows a weight of only 39 pds for the Scorpion ATR, SL rated anyway. If that's the tire you started with, that's 18 pounds per corner, lighter than the replacement. That's a pretty significant difference at 72pds total weight gain. Adding that much weight in the cab or bed wouldn't even be noticeable, but "unsprung" weight has a much bigger impact on economy and performance.

Experienced the same thing on my 21 Powerboost when upgrading from the stock Michelin's to K02's. Similar weight difference, similar impact.

 

[Old Hat]

This is exactly why I’ll stick with highway tires. Aggressive all terrains might look cool, but it would be foolish to suffer the noise, ride and MPG drop when I never go offroad.

 

[24Carbon150]

The single biggest factor that effects fuel mileage is the weight of the tires and increased rolling resistance.

 

[Jean Deaux]

I lost about 4 mpg when swapped OEM Scorpions 265/70R17 (52 lbs each) with Toyo Open Country AT3 285/70R17 (46 lbs each) on stock wheels and no lift or level. The speedometer has been recalibrated to reflect the new size. I recon the MPG loss in my case is ain't about the weight difference but the higher ride and worse aerodynamics. Frankly, I didn't expect that much of a difference but it is what it is. Especially in comparison with deleting my constantly jamming Active Air Dam and replacing it with Tremor skid plate, which caused only 1MPG loss at max (with OEM tires).

 

[wz00r2]

Increase tire weight + Increased rolling resistance = Drop in MPGs.

Add the EcoBoost motor and it's even more of a hit.

These impact the fuel milage more that the tire diameter.

 

[Ricksc]

If I was worried about MPG I would not have bought a truck. A large non aerodynamic mass will not do well. I changed wheels and tires to my liking still get 17 mpg in town. Could be better on highway if I kept it under 75, but then I would be run over. I don’t believe I could find a good MPG car to tow my trailer either.

 

[wayne1948]

I have 20” k02 on my sock rims with a front level kit. I get about18-19 mpg. I lost about 1- 1 1/2 mpg. I drive fast and highway and mountain roads

 

[Flatus]

I have 20” k02 on my sock rims with a front level kit. I get about18-19 mpg. I lost about 1- 1 1/2 mpg. I drive fast and highway and mountain roads

With 20 in tires, you should be getting 40 mpg or so.

 

[wayne1948]

Wheels are 20”!!! Nobody is going to get 40 mpg on a power boost. I don’t care what they say they are getting.

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