Are My 17" Wheels Killing My MPG's...?

It is physics. Wider, heavier tires, means more mass toward the outside of the wheel = harder to accelerate and get moving.

Going down to 15 inch oem wheels with LRR tires will get you a few mpgs for sure.

SCH-I535

 

It is my understanding that the speedometer and odometer are not connected like in older cars. while the speed will read a little under actuall, the odometer will be accurate with stock tires. everything seems to be complicated in how it works. I suggest you use a gps to see miles and compair that to odometer, or on the interstates there are some areas where they have odometer checks with mile posts.

as far as do larger wheels hurt your mpg. yes they do. larger diameter wheels put weight further from the center of the wheel and it takes more energy to get them going. also larger tires will hurt mpg also with more resistance to rolling. How much does it make? I don't know. I have heard at least a couple mpg for 17 vs 15 wheel. also if the wheels are heavy it will take more power to get them spinning.

 

My experience with my 17's seems to be the same. I get about 40 mpg in hilly suburban driving, over 5o mpg on the freeway at 70, about 45 mpg average per tank. I calculate about 2-3 mpg less than the computer readout. And the Speedometer is off by 2 mph at 70 as well. For some reason my car had 225 45 r17's (bought it used) I have considered picking up some stock 15" on craigslist to get a few more mpg's and tires are cheaper as well, but I really like the look of the 17's What kind of tires do you have on the car?

 

Possibly heavy 17's and tires that are not low rolling resistance.

What kind of wheels do you have? Post a pict for all of us to see and maybe we can find out the weight of the rim.

 

With fuel mileage, more is alway best. For me, a loss of 2-3 mpg is insignificant on any vehicle that gets excellent fuel mileage. I have the Prius 5, 17" wheels and tires on my PIP. Nice wheels have always been important to me. A slight loss of fuel mileage is a trade off. The Telsa has a 21" wheel option and the Cadillac ELR comes standard with 20" wheels. They look fantastic.

 

It sounds like you might not have LRR tires on there? That can make a significant difference in fuel economy, especially in a 17" tire size.

Even if the speedometer is dead on, the mpg displayed by the Prius is only an estimate, and it is almost always optimistic, often by as much as 5% or so.

 

I have the same problem, 17" rims with cooper zeon rs3-s tires and i'm only getting 36 mpg so far. I've only had the car for two weeks and not really driving too hard on it, was wondering if something was wrong with the car.

 

There are just so many factors it's hard to tell.

1. Driving style
2. How fast you go
3. Do you coast or stay on the gas?
4. Outside temp
5. Short trips are really bad for mileage since it's not warmed up

Could go on. Wheels *are* just one factor of many.

My wife averages about 46mpg in our Gen II so it is possible to improve!

Could also check your engine air filter.

 

During the week my trips are about 6 miles each way to and from work. I'm in Colorado Springs so I have some hills in my area. Of course with the time of year it is quite cold in the early morning when I leave for the day. As far as my driving style I usually accelerate as hard as I need to to get up to speed, or gradual if there's light traffic with nobody behind me then i'm usually in the lower to mid portion of the eco bar to maintain speed. But if that's the reason why is because of shorter trips then I could live with the lower mileage cause in the end it's qualitative, i'd just like peace of mind that nothing is wrong with my car.

 

6 mile trip in cold is the issue.

 

How does that work? It doesn't make sense to have 2 different distance measurement devices. I would be very surprised if changes to tire sizes diameter are automatically compensated for by either the speedometer or odometer.

 

The actual tire diameter should be sil

The difference is the same percentage wise, which makes it easier to see at higher speeds. 10% of 10 is 1, 10% of 100 is 10, which looks more off on a speedometer.
Did your Prius come with 15" or 17" wheels? Going off the sizes listed for the 2014 models (which I assume are the same), the tire on the 15" is slightly taller, 807 revs/mile for the 15", 819 revs/mile for the 17", so if your's came with 15" wheels, that's probably your problem. (note, wheel size is independent of tire size, to a certain point, so its not weird for the smaller wheel to have a taller tire)

I averaged 48MPG over 1800 miles on a recent trip in my '05 doing 68-78mph on cruise (whatever the speed limit was plus a few). 15" wheels, LRR tires pumped to the sidewall max of 51PSI, and a lower grille block. Sure, it rides like a truck, but I love my MPGs.

 

Its done in the computer. The computer uses the correct speed for the odometer and running the car, the speedometer just displays a slightly higher speed. I think all the car's I've used an OBD-II scanner on displayed the correct speed through OBD, even though the speedo was high. I don't know of any cars that compensate for the tire size, though. There may be a setting the dealer can change that will correct it.

 

I am going by what I have been told. many have made the same comment on other threads. in general they say that the odometer will be accurate because the warrenty goes off this. they read a little fast on the speedometer so their cars don't under state mph. I think that Honda lost a class action lawsuit due to their odometers running fast. so people would believe they were getting better mpg, and they would have car problems that would not be coverd by warrenty due to inaccurate odometer.

 

I bought it used with the 17" rims on there