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Discussion Starter #1
Hi guys did anyone else experienced big fuel consumption increase by changing tyres from 16" to 19"?

I have alfa 159 1.9 jtdm and previously with 16"tyres on I was averaging 6.5l/100km (43 MPG) now with 235/40 19" TI tyres I almost always over 8l/100km (35 MPG) + car torque on decreased quite a bit, so 20-30% changes with new tyres is that normal or I have to update the consumption meter or perhaps car engine problem?
 

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An increase is to be expected as they weigh more but I'm not sure how much it would be?
 

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How about a the wheel geometry/alignment? It can influence fuel consumption as well as the tire wear.
 

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Discussion Starter #5
Yes I'm sure it is correct I trust the company that put the tyres on my car and I also paid for the geometry/alignment (optics)

On highway with 16" I was doing 160km/h with around 42mpg and now 35mpg
 

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Yes I'm sure it is correct I trust the company that put the tyres on my car...
Have you actually checked them though?

Not unusual for the wrong pressures to be set, especially as the 19" pressures are quite high.

Tyre pressures should be checked frequently anyway, so get a pressure gauge and check them.
 

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Unless the rolling radius of the wheel /tyre is exactly the same it will throw out the speedo calibration and your calculations with it. It will also alter the engine revs for a given road speed which could alter the efficiency.
The change in consumption could be a fault that showed itself at the same time as you changed the wheels.Put your old wheels back on for a few days and see if economy improves.
 

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Discussion Starter #8
I will check the pressure then this days but I don't think that is the fault I'm sure it is with the radious and calculations

Previous 16" I think were not standard size when I bought the car as they are 205/55-16 and that is not same radious as 235/40-19, so maybe the consumption before was too low and now is fine or what
 

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Previous 16" I think were not standard size when I bought the car as they are 205/55-16 and that is not same radious as 235/40-19, so maybe the consumption before was too low and now is fine or what
Both of those sizes are correct.

p260 of your owner's manual.
 

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No.
But extra width = more drag = lower MPG.


Despite the sizes being correct, the overall gearing has changed though, but that higher gearing should mean better MPG when cruising, but worse initial acceleration.
 

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Yes - check the tyres, but alsi, go into the trip A and trip B menus and I bet you a deep sea diver that there is under 500 miles distance travelled in one of them.

i.e your avergae has just been reset and you havent done a long economy run yet....

Unless you have 20 psi in there (instead of 40) I dont see 8mpg in being 10 percent out on inflation pressure.

And dont listen to 'Mr Economy' David C either, he only got 40 mpg out his Sud by halving the rolling resistance by driving on 2 wheels, but he kept busting side bolsters and losing wing mirrors :p
 

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Yes. I can feel the drag of my 19 tyres. Previously when running towards a speed camera down hill I've had to cover the brakes. Now the speed falls away when I lift off the throttle.
 

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Discussion Starter #14
:)

Ok then thanks for info guys, I will try a new Trip B menu and see, also going for dpf removal and chipping soon so I' cant wait to get better acceleration
 

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Could be a different tyre compound as well maybe? Harder compound tyres would give you less rolling resistance wouldn't they?? Certainly the newer 'energy saving' tyres may work on that principle.

Didn't think it would be 5+ mpg though :wow:
 

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The radius is bigger resulting in the car reading less km so the consumption will look worse.
Compare the Speedo reading with the 16’s and then with the 19’s with a GPS so that you can see how much deference it made.
Your Speedo probably under reads at the moment hence the consumption looking a lot worse than what it actually is.
 

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Measure the diameter of your old tyres and compare them to your new tyres. You will probably find the Ti wheels are larger. If so, your speedo will be understating your speed putting you at risk of a speeding fine (not to mention that it'd fail an MOT if detected). The Engine RPM reading will not be affected as it is measured by counting the number of times per minute the spark plugs are sparked.
 

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Measure the diameter of your old tyres and compare them to your new tyres. You will probably find the Ti wheels are larger. If so, your speedo will be understating your speed putting you at risk of a speeding fine (not to mention that it'd fail an MOT if detected).
They are bigger, but they are still the correct size for the car.
More likely that the speedo was wildly over-reading with the smaller 205/55R16.
 

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+1
 
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