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MPG decrease with new wheels

Discussion in 'Gen 3 Prius Fuel Economy' started by trentofdestiny, Jan 30, 2014.

  1. trentofdestiny

    trentofdestiny Master Finagler

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    I have a 2012 PiP with 35k and just got to the point where the factory Yokos wouldn't grip anymore (2/32") so I got some 18x8 19lb wheels and some tires that were given to me (Pirelli PZero Nero All season 225/40/18 from a VW). Now, I know these are wider than stock and are not LRR but I didn't expect this much of a drop in mileage. My first tank with them (which was 93 octane by accident, I normally run 87) is about 350 miles when normally I get 420-480 on a tank. I reset trip b every fill up and the average for this tank is 45mpg. The average before was anywhere from 51-70 depending on if I had trips short enough to use only electric or not. When I drive, I can tell that it is different. It seems to slow itself down, in neutral, on all but the steepest downhills. Also, I find myself creeping into the PWR range on the HSI just to keep speed up. I may need an alignment for the new tires or just in general but it's definitely the tires, right? Would a switch to Michelin Primacy MXM4 GreenX take care of this? And how much do you think it would improve? I'm going to fill out the MPG questionnaire soon too.
     
  2. trentofdestiny

    trentofdestiny Master Finagler

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    - What fuel economy are you getting and how are you determining fuel economy? (trip computer or manual calculations) 45 via trip computer

    - What fuel economy are you expecting and why? 53-63 is usually where it hovers with 15" tires

    - What are the approximate outside air temps? This week 14 degrees

    - How long are your trips? About 20 mins or less. But I usually get heat on most of them so the engine is mostly if not completely warmed up

    How old is your 12v battery? What is the voltage reading of your 12v battery after sitting over night? (Method Here) didn't check...

    Have you had your alignment checked? Any pulling or abnormal tire wear? Not enough miles on replacement tires. No alignment check

    - How much of it is city vs. highway? Roughly what's the average speed in overall and and of each segment? Is there a lot of stop and go driving? Not a lot of stop and go, more highway

    - What's the terrain like of your drives? (e.g. flat, gentle hills, steep hills, etc.) gentle hills with a couple steep ones

    - What are your tire pressures? 40 all around on the 18s

    - Is your oil overfilled? (i.e. above the full mark on the dipstick) didn't check...

    - Make, model, year, engine and transmission of previous car? (e.g. 08 Honda Civic Si 2.0L 4 cylinder, manual transmission) What did you actually get on the same trips/commute? (Please give us actual numbers, not EPA ratings.) I had a 2011 Prius III that always got 46-48 and the switch to the plug in got 53-63 with combined EV-HV usage

    - What region/state are you in? (if you haven't set your location) south central PA

    - How are you trying to drive (e.g. trying to stay in electric only?) and how hard are you braking? I try to flow with traffic, I haven't been more spirited than normal

    - What modes are you using, if any? "normal", EV, power, eco? It seems normal mode is best for me. They only seem to change throttle response

    - Are you "warming up" the ICE (internal combustion engine) by letting it idle after powering on? No

    - Are you driving using D or B mode? d mode

    - HVAC settings? Are you using the heater, AC, auto mode, etc.? If using auto, what temp is it set to? I don't use auto because it wants to run the ac with the heat. I set floor, 70 degrees

    - Are you using the factory tires and wheels? If not, please indicate tire make, model and size (e.g. Goodyear Assurance Fuel Max 185/65R15). Pirelli PZero Nero 225/40/18

    - If reporting a mileage drop, did anything significant change on your car (e.g. accident, hit a curb or big pothole throwing off alignment, oil change/other maintenance/repairs, changed tires or wheels, etc.) or your commute? Changed to 18x8 19lb wheels with 225/40/18 tires

    And sorry to my readers for writing a novel ;)
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  3. GrumpyCabbie

    GrumpyCabbie Senior Member

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    People always assume tyres make no difference, but probably because previously they didn't.

    5-10% mpg loss on 23 mpg is barely noticeable.

    5-10% mpg loss on 55 mpg is.

    The Prius is finely tuned for maximum fuel economy; LRR tyres, thin, expensive 0w20 oil, sleek aerodynamics etc. It all adds up. Change one and you lose a little of the economy, but 5% here, 2% there adds up.
     
  4. trentofdestiny

    trentofdestiny Master Finagler

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    Would I lose less with LRR 18's vs the ones I have?
     
  5. GrumpyCabbie

    GrumpyCabbie Senior Member

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    I don't want to sound rude here, but LRR stands for low rolling resistance. That means there is less resistance from the tyre as you drive. The trade off is often less grip when driving hard round bends and pretty much useless grip in snow and ice.

    All Season tyres grip better in snow, ice and wet conditions but by gripping more they slow the car down ever so slightly, needing more fuel to push the car forward. It's such a small amount but does affect fuel economy. In a 23 mpg car you will barely notice the 1-2 mpg difference. In a 55 mpg you will notice the drop, as it appears you already have.

    You may notice that driving on a wet road reduces your fuel economy too. The resistance of driving through water causes slight drag which affects fuel economy.
     
  6. trentofdestiny

    trentofdestiny Master Finagler

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    I haven't noticed a difference driving through water or on wet roads. I guess we are sure it is the tires now. Just wondering if Michelin primacy mxm4 green-x LRR 225/45/18 tires would be as bad as these Pirelli tires are.
     
  7. canta

    canta Member

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    I do not fell useless gripping on snow/ice.
    just two days ago, it was snowing, and freezing temperature where some become ice on the road, specially in subdivision/home area.
    I drive ~30 mph roughly.

    my previous Hyundai Tiburon 2003 with all season tires, was a bit mess while drove on snow/ice... some occasions, I almost hitted in front of me.
    I know the issue is.. Hyundai Tiburon is heavy:D, if you hit the brake slowly, the car would slide easily on snow/ice
     
  8. fuzzy1

    fuzzy1 Senior Member

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    The situation is worse than that. Because of the non-linear behavior of the mpg scale, a tire or air drag that causes a 1 mpg loss from 25 mpg will cause a 4 mpg loss from 50 mpg. The percentage loss becomes larger as the base mpg rises (i.e. base consumption falls).

    The math becomes more clear after mpg is converted to liters/100km or gallons/100miles.
     
  9. trentofdestiny

    trentofdestiny Master Finagler

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    Perhaps Yokohama YK580 tires would be better even than the Michelins and obviously way ahead of the Pirelli A/S tires in the MPG department
     
  10. Mendel Leisk

    Mendel Leisk Senior Member

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    Your stock size is 195/65R15, right?

    Why not just chalk this up to experience, get a fresh set of Low Rolling Resistance tires, in the stock size, on the stock rims, and never sin again, LOL.

    Bridgestone Ecopia EP20 are decent, not too expensive.
     
  11. trentofdestiny

    trentofdestiny Master Finagler

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    LOL. The Yoko LRR tires I got with the 12 PiP were way longer wearing than the Bridgestones on the 11 III. But I'm finding 18" LRR tires and I think those would help my situation but not sure how much. The 18" tires I have were free otherwise I probably wouldn't have got wheels right now :p
     
  12. bisco

    bisco cookie crumbler

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    the lrr's may help, but the new wheels are still going to hurt your mpg's. are you willing to risk less improvement than you hope for on a new set of shoes? also, the larger diameter may be affecting your speedo/mpg calculation.
     
    F8L likes this.
  13. trentofdestiny

    trentofdestiny Master Finagler

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    For now I'll deal with it, but yes, I would like to get the LRR's soon. What is your recommendation, conti dws (not LRR but still not bad), Michelin primacy, or Yoko yk580?
     
  14. bisco

    bisco cookie crumbler

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    i don't have any experience. i would see what tyre rack has to say, and wait for some fellow chatters who have gone to larger wheels to respond. don't be hasty!;)
     
  15. trentofdestiny

    trentofdestiny Master Finagler

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    Thanks! ;) I did see that NineScorpion is running ~51 mpg on 18x7.5s from Drag and Conti DWS' so I know it's doable. And I think my wheels are lighter than his (hers?). Plus I'd be going with an LRR tire maybe. I really need to reign in my driving, but it was not an issue with the OE tires (because it's all engineered to put up with me).
     
  16. trentofdestiny

    trentofdestiny Master Finagler

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  17. hotrod-realtor

    hotrod-realtor Junior Member

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    I just finished lowering my car and installing a set of 17 inch BRZ wheels. Honestly felt like I had thrown out an anchor, as compared to before the tires. Took a car that was pokey and slow and somehow made THAT feel sluggish. Upside, I'm not as embarrassed to drive it. lol
     
  18. trentofdestiny

    trentofdestiny Master Finagler

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    Lol. That's similar to my situation as your wheels are like only 1 lb more than mine. What tires did you use?
     
  19. bisco

    bisco cookie crumbler

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    i wonder if 14" wheels could get me to 80 mpg...
     
  20. trentofdestiny

    trentofdestiny Master Finagler

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    Lol. I don't know if 14" wheels will fit our cars. Never looked into it. But some forged OZ 15s might be light enough. Imagine a bit of tire stretch on those like the OEM 17s