17" wheels - effect on mpg ?

Discussion in 'Gen 3 Prius Fuel Economy' started by libramento, Jul 17, 2009.

  1. libramento

    libramento New Member

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    From what I've read here, and experienced, the larger wheels on the V improve the handling, but at some sacrifice to fuel economy. Can someone explain why the fuel economy should suffer with the 17" wheels? Is it purely the additional weight?
     
  2. ggood

    ggood Senior Member

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    Weight (greater inertia to overcome) and Larger Contact Patch between tire and road (leading to greater rolling resistance).
     
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  3. ALS

    ALS Active Member

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    The tread pattern is wider thus more road friction. I've heard you lose about 2 mpg but the smile factor :D is worth it. It also pulls around .85 g's on the skid pad. Don't quote me on the G's

    Stock tire is 195/65/15
    Available 17" 215/45/17

    I understand the V comes with firmer struts and shocks as well as a bigger sway bar on top of the 17 inch wheels. It should have been renamed Touring package.
     
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  4. StevieB

    StevieB New Member

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    I'd be surprised if there is much. We have a Series V and my wife is getting around 58 MPG on her 2nd tank of fuel by trying to utilize ECO Mode as much as practical.
     
  5. stream

    stream Senior Member

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    The only official Toyota specs I've seen (it was a UK doc posted here) say it's a ~1 MPG hit with the 17" wheels. A rounding error.
     
  6. timo27

    timo27 Member

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    - I'd also guess there's a minor aerodynamic effect, due to the wider tires impingeing on a greater air surface. And, probably stickier rubber for the better handling. Again, minuscule. Enjoy the benefits! :rockon: I was longing for the bigger tires/stiffer suspension driving in the mountain twisties of VA last week.

    cheers
    T

    p.s. this leasds to a related question (everything does, I guess...) -

    Anyone know, does EPA run the tests on multiple packages and average them for their ratings, or do they do the most 'popular' (i.e., 15" w/ 196/65 rubber) options and call it a day?
     
  7. wvgasguy

    wvgasguy New Member

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    I've never seen anything to confirm that but the sway bar should be something someone could easily confirm.

    I don't think the aerodynamics someone else mentioned would play a measurable factor.

    Until someone tests a car side by side under same conditions I think everythig is simply a guess as we all have different habits and driving conditions. However I do know that in my TCH I was able to beat the EPA but 10 to 15% and with the V I am less than EPA. Others with the II thru IV are beating the EPA significantly.

    It would be nice if one of the car mags would hurry up and do a comparison. Of course they would only do a performance comparison because they have proved in the past they cannot drive a hybrid for high FE testing. They just don't "get it" when it comes to that.
     
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  8. ALS

    ALS Active Member

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    On thing I have learned trying to confirm what I heard is with
    the 17†wheeled Prius-III includes a 25% quicker steering ratio.

    Which would make a real difference in the feel and response of the car under spirited driving.
     
  9. yogadoc

    yogadoc Junior Member

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    I think any MPG hit from the 17 inch tires is negligible. The MPGs you get depend more on the terrain of your commute and your driving style than on the tire size. My commute seems like it was tailor made for the Prius. I have a V and I am crushing the EPA. Today's commute to work was 72.6 MPG on the MFD.

    [​IMG]

    The handling of the car is great. It has been the most pleasant surprise about my V, coming from and STi and an S4.
     
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  10. ken1784

    ken1784 SuperMID designer

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    Japanese drivers with 17" wheels are seeing approx 5% worse mileage than with 15".
    We suspect it is caused by wider tire tread size, heavier weight and higher rolling resistance.
    Our 15" is Bridgestone ECOPIA EP25 LRR tire.

    [email protected]
     
  11. khowardrn

    khowardrn New Member

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    How the heck did you do that mileage? I have a V and I'm only getting between 40-45 mpg. I've tried eco mode, regular mode, slow starts, fast starts..... Just can't break 45 mpg.
     
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  12. wvgasguy

    wvgasguy New Member

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    I believe there is a "hit" on milage with the 17". Difficult to prove without direct comparisons. In my TCH I was able to beat the EPA by at least 10%. In the Prius V with the 17's I have to work to just match it. Sure it is capable of crushing the EPA as shown on the monitor picture, but I can do the same by picking my route. Some people's commute are ideal, some are not. My wife drives to the kids everyday to babysit and it's about 45 miles round trip. She is aberaging between 46 and 46. If I "try" hard I can make that same route with a result around 50 to 51 (35 miles of it is hilly interstate, some groved concrete). In the TCH I could actually get 40 to 41 on this trip so I know it's not that bad of terrain so I attribute my less than stellar efforts to the tires. I'm surprised from what I've been reading though that instead of 48/51 rating it should be more like 48/55
     
  13. a priori

    a priori Canonus Curiosus

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    Reading through this post, I understand your frustration, but I'm hoping to offer some consolation . . .

    This is very true, so please don't get too concerned. I don't know how you'd be able to do a direct comparison, unless you switched out your wheel/tire combo for awhile. The only other thing is to find someone else who has had a TCH and now has a Prius II, III or IV. If you make that request and ask them to compare their mileages (TCH to EPA and 2010 Prius to EPA), perhaps you'll have a bit better idea.

    How many miles do you have on your Prius V? Remember there always is a break-in period where mileage tends to be lower. Were you always beating the EPA numbers in your TCH, or did it take some time to get there?

    I'm not certain I follow this, though I wonder if you aren't suggesting that people posting pictures of their monitor displays are just cherry picking their results. If that is the case, then we simply need to ask what overall numbers those folks are getting.

    The fact is, I've never been inclined to brag about my lowest numbers! On this point: I record every change in driving between HWY and CITY by changing my Trip A each time I change driving activity. This is how I track my CITY/HWY mileage (as reported in my signature). Interestingly enough, my high and low numbers both have come within the past 9 days! The low was for only 76.2 miles of City driving: 48.4MPG. The high was for 252.1 miles of Highway driving: 64.5MPG. (This is a bit odd, because my City FE has exceeded my Highway FE to date: 58.4 to 56.0 with my City miles being just over 30% of my driving distance and 48% of my driving time.)

    Too true. My commute is terrible for mileage purposes: 4 miles each way. I just don't drive it too often, and I spend more time driving to clients establishments (or for vacation/family events). It is very hard to try to compare your mileage to someone who has a "perfect commute." This morning I drove a suburban rush-hour "commute" for a meeting. I drove 26 miles and the FE was 66.7MPG. The fact is, I believe I was really driving "up hill" and expect better mileage on my return. (Drives like this artificially inflate what otherwise might look like my commuting mileage.)

    Before Bob Wilson points out that there are too many other variables for you to be able to single out the tires (without doing the appropriate multi-variable analysis, that is!), I'll just say the same: How can you tell? For now, I'll just agree with the Toyota engineers who've told us to expect a "hit" on FE using the 17" wheels. My only gripe is that I think I'd have my lifetime FE up over 60MPG if I had 15" wheels. The fact is, though, I'm fine with my "poor" FE performance and very pleased with the driving experience of the 17" wheels and low profile tires.:D

    Where did you get those numbers? They don't look familiar to me.
     
  14. stream

    stream Senior Member

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    Steering ratios are:
    17.6:1 for 15"
    14.6:1 for 17"

    So the 17" ratio is 17% more direct.
     
  15. stream

    stream Senior Member

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    The only official document I've seen is a Toyota UK spec sheet that says it's about a 1 MPG hit with the 17" wheels--see doc below.
     

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  16. wvgasguy

    wvgasguy New Member

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    Quote:
    Originally Posted by wvgasguy [​IMG]
    I believe there is a "hit" on milage with the 17".

    a priori:
    Reading through this post, I understand your frustration, but I'm hoping to offer some consolation . . .

    Hey, I'm not frustrated. I'm estatic to have almost 47 mpg driving without any special efforts.


    Quote:
    Originally Posted by wvgasguy [​IMG]
    Difficult to prove without direct comparisons.

    a priori:
    This is very true, so please don't get too concerned. I don't know how you'd be able to do a direct comparison, unless you switched out your wheel/tire combo for awhile. The only other thing is to find someone else who has had a TCH and now has a Prius II, III or IV. If you make that request and ask them to compare their mileages (TCH to EPA and 2010 Prius to EPA), perhaps you'll have a bit better idea.

    Actually two Prii with a full battery with the different wheels would do for me. I've made this one trip a couple dozen times with my V and know what it will do. I'm guessing if I drive one with a 15" wheel set up and exceeded my past results significantly then it's the tires. I have a friend getting a IV w/ SR soon and I may get the chance to compare.

    Quote:
    Originally Posted by wvgasguy [​IMG]
    In my TCH I was able to beat the EPA by at least 10%. In the Prius V with the 17's I have to work to just match it.

    a priori:
    How many miles do you have on your Prius V? Remember there always is a break-in period where mileage tends to be lower. Were you always beating the EPA numbers in your TCH, or did it take some time to get there?

    My TCH never seemed to have any difference from day 1. Nor has my HH.


    Quote:
    Originally Posted by wvgasguy [​IMG]
    Sure it is capable of crushing the EPA as shown on the monitor picture, but I can do the same by picking my route.

    a priori:
    I'm not certain I follow this, though I wonder if you aren't suggesting that people posting pictures of their monitor displays are just cherry picking their results. If that is the case, then we simply need to ask what overall numbers those folks are getting.

    It's easy to cherry pick. I did a drive last night just to see and got over 70mpg. But it's not typical nor a drive I would normally make. One screen shot is meaningless. Even knowing their lifetime average is meaningless in comparing.

    a priori:
    The fact is, I've never been inclined to brag about my lowest numbers! On this point: I record every change in driving between HWY and CITY by changing my Trip A each time I change driving activity. This is how I track my CITY/HWY mileage (as reported in my signature). Interestingly enough, my high and low numbers both have come within the past 9 days! The low was for only 76.2 miles of City driving: 48.4MPG. The high was for 252.1 miles of Highway driving: 64.5MPG. (This is a bit odd, because my City FE has exceeded my Highway FE to date: 58.4 to 56.0 with my City miles being just over 30% of my driving distance and 48% of my driving time.)

    Your city driving should exceed your highway driving. That's partly the reason for my low overall average. Our normal trip just about always consists of 30 miles of 70 mph highway driving which is a EPA 48 rating. Throw in the WV hills and 46 to 47 is not bad.

    Quote:
    Originally Posted by wvgasguy [​IMG]
    In the TCH I could actually get 40 to 41 on this trip so I know it's not that bad of terrain so I attribute my less than stellar efforts to the tires.

    a priori:
    Before Bob Wilson points out that there are too many other variables for you to be able to single out the tires (without doing the appropriate multi-variable analysis, that is!), I'll just say the same: How can you tell? For now, I'll just agree with the Toyota engineers who've told us to expect a "hit" on FE using the 17" wheels. My only gripe is that I think I'd have my lifetime FE up over 60MPG if I had 15" wheels. The fact is, though, I'm fine with my "poor" FE performance and very pleased with the driving experience of the 17" wheels and low profile tires.

    Well this is a trip we make 5 times a week at a minimum for the last 3 years in the TCH, the HH and now the Prius. I can average out most of the variables over the long term in that I know my winter hit, my rain hit and I can drive it consistantly between the different vehicles. If I get a chance to drive a II thru IV on the exact same route I'll feel comfortable in that I'm within a range for making some compariative analysis, especially if the tires are the only difference.

    What I am saying is if I drive a Prius II thru IV the same way I drive my V and can get 55 mpg on that trip I'm convinced it's the tires. If I get 52 mpg then it's simply the terrain. Either way I wouldn't have a Prius without the V package so it is what it is.


    Quote:
    Originally Posted by wvgasguy [​IMG]
    I'm surprised from what I've been reading though that instead of 48/51 rating it should be more like 48/55

    a priori:
    Where did you get those numbers? They don't look familiar to me.

    48 Highway / 51 City is the EPA rating of the 2010 Prius ??? I find the 48 is pretty accurate to real life as a worst expectation but even I can beat the 51 by a significant margin with the 17" wheels. I think they really lowballed the city rating.
     
  17. wvgasguy

    wvgasguy New Member

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    I also think that (this is not an automotive engineering analysis) the effect of the tires will be more significant on the Highway than the City. The reason I say that is the resistance on the highway is when the ICE may be running full time will be a full time hit on gas usage while the resistance when you're driving in the city will often simply use more battery power which though it will use up the battery faster is not always a direct relationship to gas usage. I say that because there is a lot of times the engine is running and if it is generating excess horsepower it will simply recharge the battery. That is "free energy" that would be wasted in an ICE only car. The city driving is so much more effecient than the Highway that the tire resistance has a lesser effect on gasoline consumption.

    Bob (help) you can probably understand what I am saying and give me confirmation or critism to help me understand this. I have these thoughts of theories all the time but no patience or state of mind to prove them. Does this make sense?
     
  18. yogadoc

    yogadoc Junior Member

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    I didn't cherry pick that screen shot. I have what I think is the 'ideal' commute for the Prius, and I get upper 60s to low 70s every day both ways to and from work. The only point I was trying to make is that terrain and driving style matter more than the tire size.
     
  19. wvgasguy

    wvgasguy New Member

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    Didn't say you did. "A Priori" asked if I thought you'd "cherry picked" the screen shot and I responded it's easy to do. Still, screen shots are nothing more than feel good displays. Every route is different and as you said, and I agree, some people have ideal commutes.

    Heck, I've heard for three years now how short trips kill your milage. I could show you a thousand screen shots of a cold start from my house that says they don't. It's meaningless though as when I pull out of my garage I have a steep downhill approach to the highway that is over a quarter of a mile long. When my engine comes on to warm up, it is at idle and ready to kick off by the time I get to the bottom of the hill. I can drive into town, 2 miles away and have 70 mpg showing on my indicator every time. Is that typical? For me it is, but from what I read from others it may not be. If my job was in town to the south of me I would be able to have a 65+ commute. Unfortunately all our driving is to the north of here and 50 is as good as I can get. (My wife got 43.5 last week)

    As for the effect of the 17" tires, I've driven a hybrid for three years now. I have a route that we take probably 400 times a year. I can almost predict within a couple of tenth's of a mpg what I will get based on the weather and temperature. I babied the Prius on this trip and the best I've gotten is a little over 51. If I get to drive a Prius II thru IV and get, say 55 mpg, then I'm going to feel pretty sure the tires have an effect.
     
  20. pakitt

    pakitt Senior Member

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    In Germany/EU the reported difference between official fuel consumption ratings is:
    (outside town/town/combined)
    15" 3.7L/100km - 3.9L/100km - 3.9L/100km
    17" 3.8L/100km - 4L/100km - 4L/10km

    That is, 0.1L/100km - 2.35MPG more due to 17" wheels and broader tires.

    But I can also say what difference it has made for me on my commute between 17" and 16" and smaller winter tires, since I noted the consumption each day since I bought the car up to until a week ago.

    With 17" wheels and 215/45 tires, 4.78L/100km (MFD reported).
    With 16" wheels and 195/55 tires, 4.96L/100km (and colder temperatures).
    So, essentially, no change (about 1MPG difference)...
     
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