Does Tire Size Affect Gas Mileage?
 

My grandfather use to drive semi-trucks, during the 50s. He was told to put on a taller tire to get better gas mileage. Do you think this would work out for a regular car now? I drive a 05 Honda Accord, that does good on gas mileage. I am thinking of replacing the tires, from size 205/60/16 to a 205/65/16. I found a Falken tire that keeps the same speed rating as the o.e. but is a little taller. Any thoughts? Thanks:)

Pickup truck guys have beaten this horse to death.

Stay with the OEM size rubber. If you go bigger you increase the angular moment of inertia (AMI) of the tire/wheel assembly. AMI goes up with the square of the diameter.

Increasing the diameter of the wheel means your engine has to accelerate four bigger "flywheels" every time you pull away from a stop sign or light.

Believe it or not, the Honda engineers know what they are doing.

Theoretically, getting a taller tire would hurt your FE if you do alot of in town driving. Like said above, you are adding more weight on all corners which strains the car more off the lights. However, a 205/60/16 and 205/65/16 are so close, the weight is almost a moot point. Both weigh 20 pounds (average, depends on composite and build)

Now, if you drive a lot on the highway, like those big rigs, it will help you alittle. A 205/60/16 has a 24.7" total diameter which equals 840 rotations per mile. A 205/65/16 has a 25.4" total diameter which equals 818 rotations per mile. That would lower the rpms on your transmission and should give a small FE gain, but probably not much at all...

But you probably do alot of stop and go, so I dont think the little fe gain would compensate the price of new tires..unless you need new ones anyways...

Yeah, I guess thats why, that rule, would apply to semi trucks and not regular cars. Since a semi truck does over 95% on the highway and I do maybe 60% at most.
I was wondering this becasue I am in search of some new tires. Do you think that a certain tread pattern could hurt or help mpg? Also I run my tire presure high but can you run it to high, where it would explode the tire, haha. Ok maybe not explode but do something like that. I run my tires at about 40 p.s.i. It says on the tire that 44 p.s.i. is max but what if I run 50? Thanks

I've seen 90psi in a 35psi tire, but thats just insane. 40 in a 44 is fine, 50 isnt dangerous IMO but itll be alittle bit rougher of a ride. I have 45 in 35's

I have an 03 Accord, same generation as yours. I also inflate my tires to 40PSI (max cold 44). Going higher isn't going to help MPG, so why take the risk. Hondas are designed to run efficiently. Keeping your car in very good condition, doing maintenance on schedule, rotate the tires, not carrying unnecessary weight around, changing the air filter every 12-15K miles...that will give you the best MPG along with wise driving habits. I use FP60 in the duel to keep the fuel injectors clean, it's a low dose, one ounce for every 5-6 gl of fuel. We also changed spark plugs just before 40K miles.

We have the 4cyl/5AT. More than half the time we get 35+MPG on the highway; highest we've achieved was 39. Sometimes it drops to the low 30s. Fuel quality is not consistent month to month, brand to brand.

Willhall45 -

I am using one size larger and my GPS shows that I am getting a +2% change in MPG :

New shoes (aka tires)
https://www.gassavers.org/showthread.php?t=3699

I chose these tires because I think they have an LRR (Low Rolling Resistance) pedigree.

CarloSW2

I am looking at replacing the 195/70R14 tires on my Camry with 185/75R14 tires when I can afford it. They're much cheaper and should offer a tiny improvement in MPG.

So, if I'm understanding this correctly, you get better FE from a 14 wheel than from a 15 inch wheel?

I ask this because my zx2 is the 'sport' model, part of the package is 15" instead of 14" wheels.

A 14" wheel would most likely be lighter than a 15" wheel (assuming they are both steel), but it would be a few pounds at most I would guess.

Just remember, if you get taller tires, its going to throw your gauges off a bit (speedometer, odometer, tripometer....). And that would also affect your calculations when estimating MPG's.

On the other hand, there's reason to suppose that more energy is lost in sidewall flex in a higher aspect ratio tire than a lower aspect ratio tire. Ergo a 65% 15 inch wheel with the same width as a 70% 14 inch tire may have less rolling resistance.

Driving around town this question is to complicated due to accelleration, deccleration and tire construction when turning.

In the special case of long distance driving we can make a simple case

-most gas consumption in this case is mainly replacing energy lost to wind resistance and friction. The other factors are not that significant.

- rate of gas use is related to rpm and the power curve for the engine. Regardless of what gearing you have in between all you want to know is how many times the engine turns over per distance actually travelled (not what the odometer says).
That is why we have overdrive, drive in 5th gear instaed of first, and we know higher ratio rear ends give better performance and poorer mileage.
We are just manipulating the same numbers by changing tire radius.
By extrapolation you wouldn't use 7 inch wheels and expect efficiency(your RPM would be doulbed).
Also your gas engine is upside down compared to an electric engine it has it worst performance at 0 rpm and the electric motor which is most efficient at 0 rpm. (that is why I would rather have a gas engine connected to a generator and an electric motor at each wheel-not my idea Dr Porsche toyed with this in 1925, the 4 motors)

Generally at high speed cruising lower RPM will also put you in a more favorable position in the power curve of thwe engine

Don

I had a 1994 accord with 195/60r15 tires, speedo was quite a bit off, says I was doing 70, when I was doing like 66. I put 205/60r15 tires on it, and the speedo was much closer, 70 indicated was 69. I just bought a 2002 Civic Si, recommended tire size was the same, and it came with guess what? 205/60r15 tires on it. I checked the speedo with a GPS,and its really close. just about identical to my accord. Maybe it was just a fluke, but it seems at least according to the speedo, one size larger is what it should have on it. Well it also could be my GPS if off, but I doubt it...

I know on FWD mopars they have 3 available speedo drive gears, 19, 20 and 21 teeth and a dozen possible final drive combos and a dozen factory wheel/tire size combos at least... so it gets the speedo gear that's within 5%...

...and one case where taller tires can almost certainly increase FE: My car's highest gear is way too low for highway use. I get into 5th at 30 mph, sometimes lower. The same gear runs at 3000 rpm at 70 mph. It's pretty lively on the highway without downshifting, but I wouldn't mind downshifting to get some acceleration. The car needs taller gearing (ideally through wider ratios, but that's not feasible), and the cheapest way to get it would be taller tires, though it wouldn't be a huge difference.

Depends on your driving habits, gearing, ect. A taller tire will give you different overall gearing and can help mpg...just don't go too big and go the other way.

I just changed my front tires from 195/70/R14 to 185/75/R14. It feels like it rolls better, but no numbers as they were changed mid tank. I got new steel rims with the front tires,so I may replace the back tire soon and just store the wider tires for short term need. They are only $35 each.

Slurp,

So what was the result of going with the taller tires? The difference wasn't much, but in terms of mpg, was there an increase or not?

I did that before I measured FE. sorry :(

You gotta consider the effect the larger size has on the speedo. If the computer uses speedo for management, it changes things and any benefit may be lost to the computer being confused. Also, use a GPS for milage/fuel use as the larger sized tires change odo as well. Larger tires usually cost more than stock sized so savings in fuel cost may be lost to extra cost for tires. It may not be noticable for city driving, but on hwy driving may suffer from greater wind resistance from wider/taller tires. Best bet... get 48" steel wheels (like on old prairie schooners) about two inches wide. Low rolling resistance, low wind resistance, never wear out, looks good if you get the wooden spokes painted in birght colors.

I put taller tires on my bus for the simple fact that I needed new tires, and it was cheaper to go with taller tires rather than putting on new OEM tires and changing the rear end gear ratio.

While I like the rear end ratio, I do feel that the added height of the tire allows more air than I'd like under the bus, which doesn't help my FE.

going from 205/60 (what came on my truck) to 195/75 (stock size came in the bed of my truck because they're bald) AND calculating the numbers to account for it went from 21 mpg mixed to 24.5 mpg mixed. without calculating the change, there's no difference.