Better MPG with 15" tires than 17" is this true?

If the tires were made out of steel, I would say 17 in would give you better MPG since it could glide better. However, since tires are made out of rubber, I don't know. You should check the "roll resistance" of the tires and see which one is lower. The lower one should give you better MPG

By the way, if I were to buy bigger tires, it's only because I want a more comfortable ride. And 17 inch tires should yield more miles than the 15 inch.

 

the 17's wont give more comfortable ride.......

 

of course 15in wheels give you better mpg. It takes more power to turn a 17in wheel
I believe the term was called rotational inertia?

 

If the diameter and width of the 15 and 17" tires are the same but the 17" wheels are 2 pounds liter and the 17" tires are 2 pounds liter, the 17" wheels will give better mileage, but unfortunately, the 17" wheels are wider then the 15" wheels so friction and aerodynamics come into play, weight is involved. IMHO, the 17" wheels are safer overall but ymmv

 

Another factor is LRR tires. From what I read on PC, 15" LRR tires were available earlier. There are more 17" LRR tires now but I am sure that contributes as well. As easy comparison is look at Fuelly data for owners with Prius and compare model like trim 5 or Persona, they generally have lower mpg than models with 15".

In older posts, I read reports of 5-6 mpg differences between the 2 sizes. Now the data seems to say less. My guess is it's down to 2-3mpg. I calculated the difference for average driver, about $200/year gas wise. I think it's worth the sacrifice for stability and aesthetics.

 

Low Rolling Resistance.

 

not all LRR tires are equal.. there's a lot of data on here or web.. data seems to say they do.

 

Is that right?

 

Mathematically speaking, 17 in wheels will spin less revolution than 15 in traveling the same distance. Going freeways speed, the 17 in wheels will be running in lower RPM. I think the lower RPM will give you a more comfortable ride. Of course, I do agree that most people may not feel the difference.

 

You'd think, but 215/45R17 have smaller outside diameter than 195/65R15.

 

Are you saying 17 inch is the measure of the rim, and not the tires?

 

Yes, the mileage is worse with the 17 inch wheels, by a minimum of 2 to 3 mpg, and probably more in my experience. Also, the ride is far harsher with the low profile tires. There is only a very slight increase in cornering feel and little if any effect on highway stability. 17 inch wheels are simply not worth the mpg hit or the pain.

 

Have you guys checked out these threads? They're all about wheels, tires, and mpg...

Low Rolling Resistance replacement tires: Current List | PriusChat

Gen III aftermarket wheel thread...post your pictures | PriusChat

There're many more threads on the topic if you want to know more about wheel size, LRR, and how they affect mpg, just search the forum or else google will take you to the threads.
As others attest, going from 15 to 17 definitely decreases mpg because the wheel / tire combo is heavier, unless you use a super low-weight wheel, and even then it's iffy. I'm seeing 4-5 mpg hit with an 18 lb 17x7 wheel and 215/45 tire. Also this oem-sized 17 is 20mm wider, creating more rolling resistance.
As for the ride quality, a lot depends on the tire itself. Me personally, I'm convinced my 17" Michelin Primacy MXM4's ride a lot smoother and quieter (is this a word?) than my oem 15" Yokohama S33's ever did. The ride doesn't seem harsh at all but I guess that depends on the tire.

 

He said "if" As I understand it, Toyota sizes the different diameter wheels to have the same diameter tires, so they both rotate the same number of times per mile and the speedometer and odometer do not need to be altered.
Then more of the combo is aluminum and less is rubber, improving handling and hurting ride. A minor impact on MPG is that aluminum is heavier than rubber, so the rotating weight goes up.

Consistently, however larger diameter wheels are wider (and have wider tires) than the smaller diameter wheels.
This hurts aerodynamics, and snow traction, but improves dry handling.

If your sole goal was MPG, you would run the tires with the best LRR scores, except that the US does not grade LRR like the Europeans do.

 

Exactly!

He said:

​