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Thread: Tyre size change knackered my MPG!!

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    Default Tyre size change knackered my MPG!!

    I changed my front tyres from factory fitted goodyears (sri 17 inch alloys) last weekend. Now my mpg is around 5-10% worse! Its not the cold weather, i know what i should be getting. Someone on here, said that VX can change the tyre cal in the ECU via tech2. How much would they charge for this?

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    what did u change them too?

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    Regular Member Dan_BlackSRi's Avatar
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    Tyre pressures right..? That can have a noticeable effect on mpg....

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    If your new tyres are larger rolling radius it is possible to get an improvement in mpg but still show a decrease - it's all to do with the arithmetic and gearing.

    Most (maybe all?) OE tyres are ECO low resistance fuel-conserving tyres - it's very likely that any change will increase consumption.

    Don't forget that weather, traffic conditions and driving style all affect fuel consumption so it's normal to get a variation in results, even over longer mileages.

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    Sorry re the missing info. Changed them from 215/50/17 to 225/45/17 (Sri 17 inch alloys).

    I understand about driving style etc, but I know what mpg i should be getting. It definately went with the tyre change.

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    Full Member Big Sig's Avatar
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    Are they cheap tyres or a decent brand?
    Now I need a turbo to keep up!

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    Tyre pressure should be OK, as they have just been fitted.

    The brand: they are Avon z33 (or zz3). The old ones were goodyear nct's.

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    check the pressure when garage fitted mine only put 30psi in and should have been 38psi, don't trust the garage to put correct psi

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    Quote Originally Posted by gregc View Post
    check the pressure when garage fitted mine only put 30psi in and should have been 38psi, don't trust the garage to put correct psi
    tis true...garage refused to put mine up to 43psi as they said it was way to high... even though i explained i was going on a long journey full loaded up and it said it in the book!

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    Tech2 or Op-Com can as you suspect, tell the car it has a different wheel size fitted. From looking at mine though all it does is change between 17, 18 and 19 inch to accomodate the change for wheelspeed sensors/speedo, etc.
    As has been said, I'd be looking at the cheap options before worrying out paying out more dosh.
    Pressures first - air is free

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