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19's killed fuel economy

Discussion in 'A4/A4 cabriolet/S4 forum(B6 chassis)' started by evo2audi, Jan 11, 2008.

  1. evo2audi
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    evo2audi New Member

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    Hi all, I recently fitted 19's to my whip. Car as in signature. They killed my power and seem to have hit my fuel economy hard. What gives ? Surely there isn't that much difference in weight. Anyone else notice this. I had 18's on before and there is a noticably difference when overtaking. I bent the 18's in the snow last week. Did not think 19's would affect like it has:wtf:
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  2. andyccr
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    andyccr 2003 1.8T Sport Ebony Black A4 Cabriolet

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    Went from 17s on my Octavia to 18s with no noticable difference.
    Also went from genuine 'old' RS4s to Sportec Mono10s in 19s and have noticed no real difference on fuel consumption

    Your signature says '19 RS4s' - are they cheap copies ? Maybe a heavier wheel than your originals ? What tyres ?

    A couple of variables for you to think about
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  3. chris_20
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    chris_20 Member

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    the 19s have a bigger rolling radius which in turn means the engine has to work harder to turn them. this obviously has a knock on effect of the fuel consumption but i must say ive never had any Noticeable difference.
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  4. arthurfuxake
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    arthurfuxake Controversial & Contradictive

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    Sorry Chris, you could be wrong. 19" wheels with the correct size tyres should not have a significantly different rolling radius to 18" wheels. A shift from 18" to 19" wheels requires a drop in sidewall profile to compensate for the increase in wheel diameter. Our cars have varying diameter alloys as standard, but they are all the same overall rolling radius because the tyre profiles are different.

    Evo2audi, you say that you bent your 18" wheels in the snow, I'm guessing that was caused by an impact. Have you had the tracking and alignment checked? If the impact was big enough to bend the wheel, chances are that you've knocked the alignment out, if not worse. This might be causing the increased mpg's and will make the car feel slower, as one or more of the wheels is being dragged across the road rather than rolled.
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  5. chris_20
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    chris_20 Member

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    Thats what i meant ^^ lol
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  6. evo2audi
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    evo2audi New Member

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    Had it aligned. no problems there. As you said the sidewall has decreased to compensate for the increase in size. can't figure it out
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  7. J7USS
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    J7USS Shuddup Foooool!!

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    What are the offset of these 19's??
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  8. evo2audi
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    evo2audi New Member

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    Not sure of the offset to be honest, forgive my ignorance how does the offset affect the economy/power ? please explain?
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  9. J7USS
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    J7USS Shuddup Foooool!!

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    If your offset is well out then you car feels like its running on Wooden Wheels, Hence the slowness in Roll etc (this can also be to do with your camber etc) and when you let your led foot off the accelerator it just feels like it wants to slow down if you get what Im sayin, Just general drive feels like ***** basically! You say you have had a wheel alighnment - I take it a Proper one, Not just a Kwik fit drive on Jobby!!
    Optiflex machine is what you need.
    ....Well me scooby did when my offset was totally wrong..
    Felt like I had to really give it some to get that feeling you used to get with standard wheels on.
    Im going on Power wise, I aint talking about economy because I took them off after 20miles or so..
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  10. evo2audi
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    evo2audi New Member

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    Proper alignment. Proper 4 wheel jobbie. Don't know what is going on. I went from 17 to 18 on my Evo and noticed no difference at all.
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  11. ChuckH
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    ChuckH Member

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    What He means is that as the size of the rim goes up The depth of the sidewall of the tyre generaly decreases
    So in effect the overall outside diamiter of the wheel/tyre combo should remain the same !

    There is no real reason why Your wheel swap should adversley affect the fuel economy !!
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  12. terrysingh
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    terrysingh Member

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    heres the techy bit, the reason your car runs worse on 19" compared to 17" and 18" is the wheels rotational mass changes i.e. where the was rubber and air there is now metal, causing a drag on the engine hence the drop in performance and mpg....

    so i've been told?
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  13. dan_b
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    dan_b Member

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    I'll add to the above with a few pointers.

    Are the brand of tyres the same? A more sticky tyre should in theory reduce MPG.

    Also, are the new tyres wider than the old 18s? Again, with more rubber in contact with the road, you've got more drag, therefore poorer MPG.

    In addition, is the rolling radius actually the same (ie. are you sure you've got the correct profile ratio on the new tyre)? As above, a bigger diameter will not only give a bigger rotational mass, but also a longer contact patch on the road, which will as before reduce MPG.

    On top of that, the newer wheels themselves may be just a bit heavier - that extra inch diameter of metal could well weigh a bit more. Again you're into increased rotational mass there.

    Finally (phew!), check your tyre pressures - low pressures can reduce MPG.
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  14. evo2audi
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    evo2audi New Member

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    The tyres are continental. the pressure is spot on. guess if i want the look that is the compromise. something to bear in mind for all you out there. Incidentally what pressure are you 19" boys runnin ?
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  15. J7USS
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    J7USS Shuddup Foooool!!

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    36 rears,34 fronts..
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  16. golf
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    golf ***** rent boy

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    I run 36 PSI all round.
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  17. dan_b
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    dan_b Member

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    All sounds ok then - are you sure something else didn't get knocked/ damaged when you kerbed the wheels in the snow? Perhaps a sensor has come off, or something is on the blink?
    #17

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