Tire size versus fuel economy


#1

I have heard numerous opinions on this subject, and I would like to know the correct answer.



All other things being constant,If you increase the diameter of your tires (buy larger tires), does this increase or decrease your fuel efficiency (MPG) over a given distance?



I assume this is over a measured distance, using GPS or map, since the odometer would not be accurate in speed or distance traveled.



In advance, thanks for your answer.


#2

If your vehicle was designed to get good mileage, odds are that changing the tire size in either direction will have a negative effect.

If your vehicle was designed to pull a trailer, for instance, and you are more interested in high mileage, then larger tires will translate to fewer engine revolutions per mile, and may get you better miieage.

Now, narrower tires are generally better for any vehicle, because given the same tire structure, narrower tires have less wind resistance and less rolling resistance. They don’t look nearly as good, though, and generally don’t stop the car as well on pavement.


#3

The larger tire (in diameter) will lower your engine RPM when compared to the smaller diameter tire at the same speed.The question is is this lower RPM a better RPM in regards to where your engine is most efficient. We have bounced this discussion around quite a bit (people that are quite certain that they get better mileage at a higher speed than a lower speed,they feel the higher speed puts their engine into its “sweet spot” where its get better mileage)this goes against what you would think,going faster requires more power so its going to use more fuel,but people are certain with their paticular vehicle they can go faster and get better mileage.


#4
Today most cars are designed to provide the greatest mileage.  It helps sell cars.  The manufacturers know how to provide increased mileage for the average driver so they take that into account.  

The only way you are likely to come out ahead, is if your driving is not average.  Most of the time you are going to loose if you change.

#5

There is no correct answer. Whether you gain or lose depends on too many different variables. As others have pointed out, the marketplace and the feds (via CAFE requirements) have compelled the manufacturers to design drivetrains (of which the tires are ultmately a part if you consider that their rolling circumference is part of the ultimate drive ratio) that provide optimum gas mileage with satisfactor performance for the target market.

Gains in one area come with compromises in another area. The car’s designers have generally pretty well optimized the overall design for you. You could increase your mileage by pumping your tires to the max pressure on the sidewall, but the compromises in safety (this one cannot be overemphasized), ride, handling, and wear make it a losing proposition.


#6

I believe that the majority of newer cars are geared as high or higher than they need to be. A lot of them can barely pull an overdrive. I believe that larger tires would only add to less power and no increase in fuel mileage. I bought a new '94 Dodge Ram with V8, overdrive , a 3.50 to 1 rear axle, and 16 inch tires. That truck didn’t need an overdrive. It would run 70 mph at 1750 rpm. It was more powerful at about 2000 to 2200 rpm.


#7

Vehicle would be higher and that usually cuts the gas mileage. They are also harder to steer.


#8

IMHO the difference in negligible. For people I know with Subaru WRX’s who install 16"(stock), 17"(factory upgrade) or 18"(light aftermarket wheels) the difference in MPG is not measurable.


#9

Larger Diameter tires may NOT increase the gas mileage…At least not significantly.

Decreasing the width will help more…HOWEVER you run the risk of decreased handling.


#10

Andrew, you’re talking about the wheel diameter. The OP is talking about the tire diameter. Withe the proper sized tire, wheel diameter can be increased without significantly changing the outside tire diameter.

For example, a 215x45 tire on a 17" wheel is comparable in outside diameter to a 215/40 tire on an 18" wheel.

www.carbibles.com has a good primer on wheels and tires. I recommend a visit.


#11

Andrew might have been talking about wheels but I assume he meant to put tires on them!!!