Does tire diameter affect gas milage?

[JEDI]

The bigger the tire, the worse the car's gas milage?

Esplain pls

 

[thetxstang]

More rolling resistance?

 

[imported_goku]

More rotational mass, though if you have 7" wheels you may have to spin them faster to go the same speed so it would negate the fuel savings of not having to rotate all of that mass, unless of course you've got big tires on small rims.

 

[Jeff7181]

It's not quite that simple... using a larger diameter tire does the same thing as using a numerically lower gear ratio, which translates to lower engine RPM, and usually better gas mileage assuming it's not so low that you "lug" the engine.

 

[NTB]

it might, if you make a fairly large change - significantly bigger wheels and tires will be heavier, so they require more power in order to turn

On the other hand, if you replace a steel wheel / hubcab combo with an aluminum or alloy wheel and tire of the same size, or maybe an inch or so larger, these may actually be lighter than the stock wheels. So your gas mileage probably won't change, or it may go up just a bit.

Then again, I may be way off the mark But at least it seems logical that way.

Nate

 

[Sluggo]

Frankly if your tires are only 16" in diameter you must be driving a tricycle or something.

Even a 215/60/16 is going to be about 26" diameter, and thats a pretty average tire size.

 

[Pacfanweb]

It works several ways:

1. Yes, there is some added friction with a larger tire. More weight. But this is negligible.

2. A taller tire makes you turn less RPM at the same speed....so it's like slightly raising your gear ratio. Again, probably not noticeable unless you made a DRASTIC jump in tire size.

All in all, the pros and cons pretty much cancel each other out and you won't likely notice a difference with going a couple sizes bigger (e.g., from a 245-70-16 to a 255-70-16)

Now, if you have a 4X4 and you lift it and put some big mud tires on there, you WILL see some difference in mileage and power if you don't re-gear it to compensate for the taller tire. (e.g., lifting your Suburban and going from 265-70-16's to say, 35's.)

 

[imported_LoKe]

Larger tire = fewer rotations.

 

[Evadman]

Originally posted by: Pacfanweb
Now, if you have a 4X4 and you lift it and put some big mud tires on there, you WILL see some difference in mileage and power if you don't re-gear it to compensate for the taller tire. (e.g., lifting your Suburban and going from 265-70-16's to say, 35's.)

That is not entirely true. The tread type (both compound and design) affect your gas millege drasticly. When I switched to a set of 33 x 10.50 R16 Thornbirds from the regular set (almost exactly the same size as the 285 75 R16's) my gas millege went down by 33% (little over 9 to a little over 6) and if anything, I drove slower on the thornbirds because I didn't want them coming apart (which they did anyway, and took my passenger side rocker panel with them BTW) But they were always HOT after I drove any decent distance. Like 140+ degrees hot, you couldn't touch them. (just guessing on temp, I never measured them. But they were too hot to touch)

So it is not just the diameter and weigth that make a difference, but the rolling resistance. and let me tell you, thornbirds have some resistance. I was going to get boggers, but it probably didn't matter.

 

[Fenixgoon]

bigger wheel/tire = larger rotational inertia = more energy spent turning wheels = less gas mileage. also, sometimes if you change to larger wheels/tires your speedometer will no longer be accurate

 

[Pacfanweb]

Originally posted by: Evadman

Originally posted by: Pacfanweb
Now, if you have a 4X4 and you lift it and put some big mud tires on there, you WILL see some difference in mileage and power if you don't re-gear it to compensate for the taller tire. (e.g., lifting your Suburban and going from 265-70-16's to say, 35's.)

That is not entirely true. The tread type (both compound and design) affect your gas millege drasticly. When I switched to a set of 33 x 10.50 R16 Thornbirds from the regular set (almost exactly the same size as the 285 75 R16's) my gas millege went down by 33% (little over 9 to a little over 6) and if anything, I drove slower on the thornbirds because I didn't want them coming apart (which they did anyway, and took my passenger side rocker panel with them BTW) But they were always HOT after I drove any decent distance. Like 140+ degrees hot, you couldn't touch them. (just guessing on temp, I never measured them. But they were too hot to touch)

So it is not just the diameter and weigth that make a difference, but the rolling resistance. and let me tell you, thornbirds have some resistance. I was going to get boggers, but it probably didn't matter.

So you just agreed with me, but added in the softer tire factor, which Interco tires are known for.
Edit: Softer tires or more aggressive tread will have a lot more rolling resistance or friction, and can definitely reduce mileage.

And you bought Thornbirds? LOL.

 

[Pacfanweb]

Originally posted by: Fenixgoon
bigger wheel/tire = larger rotational inertia = more energy spent turning wheels = less gas mileage. also, sometimes if you change to larger wheels/tires your speedometer will no longer be accurate

Actually, that's EVERY time you change to larger tires the speedo won't be accurate.

Then again, most speedos aren't accurute to begin with, they read a bit faster than you are actually going.
So going up a couple of sizes will make the reading a bit closer. But if it was correct to start with, then putting taller tires (the rim size is irrelevant, only the outside diameter of the tire matters) will throw it off.

 

[Pacfanweb]

Just re-read the topic, and saw the OP asked about 14, 15, and 16" tires and if they made a difference.

The wheel (rim) diameter is completely irrelevant.

The only thing that will affect what we're discussing here is the outside diameter of the tire. If you go from 15" to 18" rims, and your tires are still the same height, then there will be no difference.

 

[Theguynextdoor]

The problem with this is the larger wheels have lower profile tires.

 

[Evadman]

Originally posted by: Pacfanweb

Originally posted by: Evadman

So you just agreed with me, but added in the softer tire factor, which Interco tires are known for. And you bought Thornbirds? LOL.

thats why I said 'not entirely true' the tires were almost exactly the same size and I lost 33% off my MPG. that is insane.

And yes, I bought thornbirds. Never again. I was on my way to the WI Dells and the tread started coming off one of the fronts. So I swapped to my spare. Then, the tread came off the other one. Not a little either, it came off like it did on the expolders. Aparently, they 'forgot' to bond the tread to the carcas or something. The rubber was actually sticky. I have always been told that vulkanized rubber is not stickey. So yea, no more Interco tires for me unless it is on a really light vehicle instead of one only a few hundred lbs under the weight rating.

gotta give them props though, the carcas still held air, even without the tread, and survived a drive of about 10 miles to the next exit and a walmart that had tires.

Originally posted by: Pacfanweb
The only thing that will affect what we're discussing here is the outside diameter of the tire. If you go from 15" to 18" rims, and your tires are still the same height, then there will be no difference.

Come on, you know better than that. A larger rim will have more weight, thus take more power to get up to speed. It will also take longer to stop. In addtion to riding like crap. Tires do a lot of the work of the suspension absorbing bumps.

Also, the tire (in some instances) will actually weigh more in a larger rim size as there is actually more steel in it than a smaller rim size.

 

[Pacfanweb]

Originally posted by: Theguynextdoor
The problem with this is the larger wheels have lower profile tires.

Not if they put taller tires on them when switching the rims.

If you change to bigger rims but keep the same height tire, then yes, the profile (sidewall height) will be smaller.

But if you put larger rims, along with a corresponding larger diameter tire, the profile either won't change or may even get bigger.

 

[OS]

Originally posted by: Pacfanweb
Just re-read the topic, and saw the OP asked about 14, 15, and 16" tires and if they made a difference.

The wheel (rim) diameter is completely irrelevant.

The only thing that will affect what we're discussing here is the outside diameter of the tire. If you go from 15" to 18" rims, and your tires are still the same height, then there will be no difference.

well, typically larger rims will weigh more, that may affect gas mileage somewhat, even if total wheel size is kept same. Not a huge amount, but likely measurable in a controlled test.

Oh yeah another consideration, going to a rim with a larger diameter increases rotational inertia to the square, even if the rim weight is the same.

 

[fitzov]

As with any gear system, an increase in the radius of a wheel increases the amount of torque, so you don't need as much force to turn the wheel.

And the increased circumference means less rpm for the same distance. But I'm not sure this translates into the engine being more efficient.

 

[Pacfanweb]

Originally posted by: OS

Originally posted by: Pacfanweb
Just re-read the topic, and saw the OP asked about 14, 15, and 16" tires and if they made a difference.

The wheel (rim) diameter is completely irrelevant.

The only thing that will affect what we're discussing here is the outside diameter of the tire. If you go from 15" to 18" rims, and your tires are still the same height, then there will be no difference.

well, typically larger rims will weigh more, that may affect gas mileage somewhat, even if total wheel size is kept same. Not a huge amount, but likely measurable in a controlled test.

Oh yeah another consideration, going to a rim with a larger diameter increases rotational inertia to the square, even if the rim weight is the same.

Regardless, it is irrelevant to gas mileage. The difference won't be noticeable.

 

[Colt45]

rim size isnt the issue. youve got two..

1. overall wheel weight
2. overall wheel size (not rim).. this is just like changing the gear ratio though

 

[HomeAppraiser]

Originally posted by: LoKe
Larger tire = fewer rotations.

That is my uneducated guess also. The weight of a larger tire is nothing compared to the overall weight of the car. What I want to know is why all of the "High Mileage Champ" cars like Geo, Civics etc. always have tiny tires?

 

[B00ne]

Originally posted by: JEDI
The bigger the tire, the worse the car's gas milage?

Esplain pls

your speedometer and odometer will be off, Dunno howit in the US but here you cant just use a random tire-rim combination. The circumference of the wheel should stay eaqual. so if you put on bigger rims you need a smaller profile tire.
The number that you give are rime sizes and not tire size. The tire size depends on several factors first you have the rim size (inner diameter of the tire, 14", 15" etc in inch) then you have the width of the tire (the 195, 205, etc. in mm) and third you have the tire hight in percent of the width. All this together gives the diameter (circumference)

 

[BoomerD]

I wonder if the OP was referring to replacing stock tires with the "plus 1 or plus 2, 3 etc)" type of upgrade. Pretty common nowdays. IF that's the case, as long as you match rolling distance (diameter is usually pretty close) then you shouldn't notice a change in mileage, everything else being the same, (tire quality and construction) Sites like Tire Rack will let you know exactly how many revolutions per mile a certain tire makes, to make it easier to match cmore closely. You WILL lose sidewall height, (and IMO ride quality) but gain some handling as the sidewalls are shorter, so they flex less...that's the idea behind low profile tires...Many people IMO go way too far, and essentially, end up with HUGE wheels with black rubberbands on them...That usually leads to bent wheels about the first pothole or speed bump you hit too quickly...
OTHERWISE, if you're talking abour replacing stock wheel & tire combos with larger wheel/tire combos, (as in Monster truck fashion, then read the other posts, as many are right on with their info...