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MPG Drop since tyre allignment

Discussion in 'Gen 3 Prius Fuel Economy' started by GrumpyCabbie, Mar 19, 2010.

  1. GrumpyCabbie

    GrumpyCabbie Senior Member

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    The tracking/allignment was out on my car and it started to chew the inside edge of my tyres, until they were getting borderline illegal at 12.5k miles. The outside edge was ok and had about 3mm. I do loads of town/city driving and normally expect 17k miles out of a set of front tyres! But 12.5k is low even for me :(

    Had the main dealer do the wheel allignment and replaced the tyres with like for like Bridgestones. They matched the price of a local tyre warehouse so the cost was very good.

    However, I have since noticed that my fuel economy is down by about 3-5 mpg on average! I checked the tyre pressures and noticed they had only pumped them to 31 psi not 37. Not a good start so I pumped them to the correct psi and hoped that would improve the fuel economy. It hasn't.

    I'm now halfway through my second tank of fuel since the new tyres and the trip computer is at 48 mpg (works out 45 mpg true) when I normally get about 51 mpg (48 mpg true). (I have a lead right foot :rolleyes: )

    I though maybe they hadn't adjusted the tracking correctly but the car handles fine, holds a straight line and actually takes corners better. Could it have been that the car was running on the inner edge of the old tyres with the allignment out and as such this gave less resistance and better mpg? It did tramline a little in the wet just before I changed the tyres. Or do new tyres take a little time to wear in?

    Any advice appreciated :)
     
    #1 GrumpyCabbie, Mar 19, 2010
  2. bwilson4web

    bwilson4web BMW i3 and Model 3

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    We've had quite a row over getting tire rolling resistance published. California has an initiative and so too has the Dept. of Transportation. But sad to say, no results!

    So far, the only source I've found has been Consumer Reports. I don't have it handy but they listed the Sumitomo T4s as low rolling resistance and that is what I use on our 2003 Prius. So far, no complaints. The first set lasted 50k miles but was lost due to a sidewall puncture. I'm now on my second set and they have met expectations.

    I have read some good reports on other, low rolling resistance tires but they tend to be a little pricier than I care for.

    Bob Wilson
     
    #2 bwilson4web, Mar 19, 2010
  3. GrumpyCabbie

    GrumpyCabbie Senior Member

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    But the new tyres are the same make and type as the Bridgestones they replaced, so should give very similar rolling resistance, or do they need to 'bed' in?
     
    #3 GrumpyCabbie, Mar 19, 2010
  4. Mike Dimmick

    Mike Dimmick Active Member

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    New tyres often have freeing compounds on the surface to free them from the moulds. That in itself can have poor grip which leads to poor mileage.

    As tyres wear down, their diameter and therefore circumference decrease. The car doesn't really measure distance travelled, it measures number of revolutions of the wheels. The car therefore over-reports the distance travelled, compared to the new tyre.

    If they had to disconnect your 12V battery, you probably lost your stored MPG data. There are reportedly some compensating factors in the calculated MPG data which are also lost, and take some time to build back up, so initial estimates displayed on the car's displays can be inaccurate.

    And finally, the biggest reason: conditions vary. It has been warming up this week so I would expect it to be better than last week. Still, if you've done more high-speed journeys than usual your fuel consumption will be higher, and there's no getting around that.

    As you have a 2010 I'm not sure what tyres you have. The Bridgestone Turanza ER30s that came with the Gen 2 Prius in the UK are a summer tyre and not specifically low rolling resistance.

    In the US, owners noticed significant differences between the OE Goodyear Integrity and the aftermarket version. The reason? It appears that the OE tyre is actually made in Japan by Sumitomo, branded Goodyear, rather than being an American-made tyre. Sumitomo and Goodyear have an agreement to each manufacture the other's brands in their own home country. Bridgestone is a Japanese company, but has plants all over the world - it's possible that the compounds aren't quite the same if they're made in Europe rather than in Japan.
     
    #4 Mike Dimmick, Mar 19, 2010
  5. GrumpyCabbie

    GrumpyCabbie Senior Member

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    Aha. Now this makes sense. I travel 10 hours a day in my car and know it inside out. I know what mpg it should read in given circumstances and I know the car is just not as good since the change and the weather is warmer now too.

    I will check the side walls of the tyres to see if they are made at the same plant, or whether some are made in Japan and others in Poland or India.
     
    #5 GrumpyCabbie, Mar 19, 2010
  6. Wiserone

    Wiserone Member

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    ALL tires have a outer layer that needs to wear away before you can get better traction/lower rolling resistance.

    I forget where I read this, but it was from a reputable hypermiler website.

    Just stick it out, it will be better soon.
     
    #6 Wiserone, Mar 20, 2010
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