Smaller Tires = Better Milage?

Interesting thought --

Something just tells me that the increase in tire size over the last decade or so, is just more 'super-sizing' at the expense of a reasonable consumer.

I know that modern cars are eons ahead of of those of the 60's, but how about this --

My 1st car, a '65 Impala with 6-cyl. 140 HP had 7.35x14 tires (bias-ply sizing). 14-inchers on that big, but light-weight (~2750 lb.) boat.

Go figure.

 

I've heard (read) other blog's indicating when they 'tricked' out thier Prius (yes it's been done) that the gas milage decreases with changing form 15 or 16" tires to low profile 17's.
I dont think changing the type of 15's will make much difference as long as they are still 'hard' tires rather then the smoother riding 'soft' tires.
Hard is better for milage, but rougher noisier ride.

 

One consideration is that you will be getting more RPM's with a smaller tire. Therefore your speedometer and odometer will read higher, giving you a false reading of going faster and getting better MPG's.

Stay with a tire size of about 24.5" and around 855 RPM's in order to keep your gauge's accurate.

2 cents.

 

I don't think you will get the result you are thinking you will. A smaller diameter will yield a higher rpm. 2R * Pie would be your circumference.

So, let's see:

2R*(pi) or 2*11.2535 *(3.14) = 70.91 inches around
2R*(pi) or 2*12.25 *(3.14) = 76.97 inches around

So you are going to lose 6.06 inches of rotation for every revolution of the wheel. I don't know about other factors but it seems the engine/motor will be working harder to get the same distance.

 

wouldn't rpm's vary with mph?

 

I believe "RPM" in this case would be "Revolutions Per Mile".

 

thanks!

 

I imagine we'll see a Prius with rims like this real soon...

 

Hi All,

What about original VW Beetle tires? The rims would need to be custom, or adapted to the Toyota bolt pattern. These were 15 inch rims, I believe. And the tires were near square in section. So, the overall diameter might be close.

 

Yup.

 

Its an interesting question. Smaller tires generally equate to faster acceleration but lower top speed. I believe its more or less equivalent to making your overall gear ratio a little shorter. In general this is equated with lower fuel economy, as you will have higher engine rpms at a given speed. On the Prius its not quite so straight forward of course due to eCVT.

Lighter tires and wheels should make a difference (reduces unsprung weight/moment of inertia), so if your smaller tires and wheels were also considerably lighter that might be a consideration.

Rob

 

Someone please correct me if I am wrong, but usually a taller tire will increase fuel economy (if all other factors remain the same). I get much better mileage on my Camaro with 28" tall tires as opposed to the stock 26" tall tires. It is also slower on takeoff but has a higher top speed.

I believe you will need to reprogram the computer somehow to accomodate a shorter (or taller) tire as the automatic transmission (at least in other cars) is programmed based on speed and revolutions in a curve to provide the best economy and performance. You will also want to correct the accuracy of the odometer and speedometer.

A tire that is shorter and more narrow "may" depending on everything else, provide less rolling resistenace which is good for improving miles per gallon but bad for braking distances and cornering (generally). Also, the more revolutions a tire makes the higher the wear to it is possible the increased wear may outweigh the increased miles per gallon and decreased safety factors... The choice is yours. I'm the type of fellow who will try just about anything so give it a try and report back as that is the only real way to know how many things work anyway.....

 

I did the same thing. I would just make sure the load rating is with-in 100 - 200 pounds of the stock 185-65-15 tire. I myself went with a slightly different setup a 175-65-15 and its working beautifully. Crosswinds from bridges and semi-trucks will be more of an issue. My mpg has not changed since I tend to drive at a higher speeds on the freeway between 75-80mph.

*I forgot to mention that I am averaging 47-49mpg @ 75-80mph on the freeway...

 

Yes, absolutely correct. Plus, a smaller wheel will present a reduced inertial rolling force to the drivetrain and you will accelerate a bit quicker (why do you think a fork lift always has small wheels?). But, I believe the increase of wheel rpm will fool the electronics into thinking you're going farther than you are, resulting in a 'biased' mpg result.
So, the bottom line: sure you will see an increased mpg but how real is it?