Larger wheels & gas milage


#1

i want to change my wheel on my 2001 ford f150 from 16in to 20in will that hurt my gas milage?


#2

Probably, because the larger wheels are likely to weigh more than the standard wheels. Adding weight to a vehicle reduces gas mileage.


#3

It depends mostly on the rolling and to a small extent, the wind resistance of the new tires if wider. Your speedometer, if not corrected if the outside diameter of your new tires is larger, will register fewer miles which will make you think that the gas mileage has gone down when in fact it may have gone up because the engine will run more slowly, creating less friction. Heavier wheels will not affect your mileage under steady driving as on a trip and otherwise, the change in weight will be negligible. The answer is not easy to come by, is it?


#4

There are several issues.

First the answer to your question is Maybe. It all depends on the rolling resistance of the different tyres, their outside circumference, their total weight, your drying style, the type of driving you do and a number of the characteristics of your car. In other words no one can answer the question for you.

The second point is that the indicated mileage is likely to change mostly based on the outside circumference of the tyres. Any change in the outside circumference will change the odometer and speedometer readings because you car will not know how far it is really traveling. Complicating this is the fact that the sizes (16" and 20") you gave us are not the outside circumference nor is it possible to compute it based on that number since that is only the wheel size. Different tyres may be taller or shorter so the outside circumference of the tyres on the 16" rims may be larger than the circumference of the tyres on the 20" wheels.


#5

I would say that the chances are that it will lower your fuel economy. It takes more torque to turn a larger wheel with all other things equal. Think about the gears on a rear bicycle wheel and how they relate to the size of the wheel. However, if it has a manual transmission, you should compensate by shifting at higher RPMs, which will also lower your fuel economy.

You drive a Ford F-150 and you are worried about gas mileage? People who drive trucks and upgrade wheel size don’t care about fuel economy. They only care about compensating for inadequacy as a male.


#6

The main factor will be the tire (not wheel) diameter, a larger wheel diameter will effectively increase your gear ratio and may improve you mileage slightly. However, heavier and/or wider tires/wheels will tend to hurt your mileage. Changing the tire diameter will also affect you speedometer/odometer calibration.

http://www.miata.net/garage/tirecalc.html


#7

With 20" wheels I’m assuming you will be running low profile tires and not off road tires? Post up your old and new tire size (not wheel size), and we can determine weather or not the change will be significant and if regearing you axle is necessary.

If the tire OD does change, the speedometer can be recalibrated for the new tires. This is very common and easy to do.

The weight difference will most likely have a negligible affect on fuel economy for this truck. Rolling resistance is more significant, but still much less significant than the overall diameter change. If you are buying high performance street tires they may even have a lower rolling resistance than your stock tires.


#8

Arent we really talking about choosing between 12 MPG and say, 8 MPG??? LOL


#9

Assuming your truck is a regular cab 2wd, your current tires should be 235/70-16, if you upgrade to 20" rims, you’ll want a 275/45-20 tire.
http://www.tirerack.com


#10

you bet it will, but it’s a matter of inertia (more specifically the moment of inertia) and kinetic energy. the bigger the tire and the further it is from the axis of rotation the higher the kinetic energy you need to start and stop the truck, will you notice it, you bet you will with those big 20"ers but I’m guessing if you can afford those tires the added gas won’t be that big a deal either. Enjoy the ride up there…


#11

I have been running oversize off road tires for years. The inertia increase is insignificant compared to the diameter change when it comes to fuel economy. That will change a little when you get up to huge rubber…like 37 - 44in tires, but we’re talking about outer diameters close to stock.

The mass moment of inertia may actually be lower if he runs the tire wheel combo posted by “bscar” There is an easy way to check this:

1.Take the new tire/wheel combo and one of the old tire/wheel combo and set them side-by-side on an incline

  1. release both at the same time; the tire/wheel package with the lower mass moment of inertia will accelerate faster than the other. I bet they will be pretty close:)

#12

That’s a good recommendation; as the overall increase in diameter is only 0.78in, which is 2.6%. This in not enough to justify a gear ratio change and will have very little affect on fuel economy.


#13

You do bring up a good point, perhaps an upgrade for the truck’s brake system would help compensate for that, and help fill out the wheels too.


#14

It will, but probably not by a measurable amount. Could be a drop of up to 5% or so. You must first determine the change in the odometer so when you calculate the new mileage, you include it or mileage will appear worse than it really is.


#15
  1. desperately chase two runaway tires rolling down the hill. :slight_smile:

Actually, I doubt this test would produce useful information unless you had a way to keep the tires going in a straight line and not wobbling. More difficult than you’d think…


#16

I’ve done it before; they roll straight. Even my skinny, tall mud tires roll straight. Best results are from a very shallow incline, so the tires don’t go very fast.