Bigger Tires Lower MPG

[Luvnlife]

I’ve read here about bigger tires causing loss of fuel mileage. I need the physics explained to me. If I replace my stock 275/55R20s with 285/65R20s I will be going from a 31.9” tire to a 34.5” diameter tire. I understand the wider heavier tire but, in effect with the larger tire I am probably reducing my final drive ratio from 3.43 - to what, 3.08. At that ratio my engine is not turning as high RPM for the same speed. Less RPM 

less fuel?

[Daly]

Heavier tires, more power needed to get the tires rotating, typically bigger tires are A/T's or M/T's which have horrible aerodynamics, and a leveling kit is usually used to achieve the fit of bigger tires, again effecting aerodynamics.

[allblack16]

Installed a 3" level and 33" mud tires on my 2016 and lost about 2 mpg. Looks cool though 

[Ozer]

Then there is the miles traveled part, your speedo will be off and calculated miles and mpg will also be off on the dash.

Just drive it and enjoy, at most 2-3 mpg is what you are loosing.

[aseibel]

In city traffic it's about the extra inertia of the heavier wheels in stop and go traffic. On the highway, you are killing the carefully engineered airflow around the front/ under of the truck. Your gear ratio is almost irrelevant to the situation.

 

Maybe if you could set the cruise at 40 mph and never stop, then your theory is correct. But that doesn't happen in real life.

 

Larger tires just create more work for your engine to overcome, therefore you burn more gas.

 

If looks are more important to you, put on the tires you want and don't look at the MPG on your display. If MPG is more important, don't get bigger than stock tires.

[Grumpy Bear]

Flywheel effect is what your dealing with. More precisely inertia moment. It's not just how much a tire weights but how far from the center of rotation that weight rest. For instance there is more negative effect gaining 3 lbs. of tire weight than there is in 3 lbs. of rim weight. Even if the lighter tire is the larger in diameter, chances are better that even that moving that lighter weight further out will do the same or more harm. I'd actually have to work the equation with precise weights and measures. There is also this; AT tires weight is in larger part in the tread than an A/S tires sidewall thus most of what kills an AT tire's economy has more to do with distance than mass and yes, tread squirm is never good either. It's hard to account for all variables but it is possible. It's why we use 'rules of thumb'. So tedious calculations don't have to be learned and repeated.  Naturally, most ignore them, rules that is. 

 

Yes the overall gear ratio will be lower and no, not a chance it will offset the weight and distance negatives. 

[Luvnlife]

Thanks members.

[Boardmember]

This was a useful lesson.