182 Cup 16's

[mantis946]

Helloha
I moved up from my origonal set of 15's to the 182 anthracites and my MPG has dropped quite alot, im betting my lucky penny on the tyre circumference changing being the culprit.
I used to pull 42 MPG now im around 35 :S My question is can i get the speedo re-programmed to show the true MPG or is the MPG calculated another way i have not considered...
Thanks

 

[TOGUSA]

technicaly because you have changed the size of the wheels and tyres etc and tyre circumference, you have affected your gearing on the gearbox, you have effectivly changed the ratios, so your car is having to work harder to attain the same speeds i.e use more fuel to do the same thing.
so thats why your mpg has gone down, cos when the car left the factory it was all setup and geard towards the 15's and now youve changed that.
if somone could back me up on that that would be cool lol

im sure thats what your experiancing anyway
hope this helps shine some light on this

 

[ripp]

plus the 182 wheels are HEAVYYYY

 

[l0rd]

Easily explained.

If you had 195s on 15" then you have about 780mm of tyre width
now, if you run 205s on 16" you have 220mm of tyre width

220-180= 40mm of tyre width extra.

Extra tyre-road surface means more petrol as there is more friction.

 

[Dave..]

Easily explained.

If you had 195s on 15" then you have about 780mm of tyre width
now, if you run 205s on 16" you have 220mm of tyre width

220-180= 40mm of tyre width extra.

Extra tyre-road surface means more petrol as there is more friction.

That's b****cks.

What has happened, is you have increased the rolling radius of the wheel, which means to cover the same distance on the 16's, as you were covering on the 15's, requires less turning of the wheel. This tricks the odometer into thinking you've done less mileage, when in actual fact you haven't.

You'll still be using the same amount of fuel, but the computer will think you've been doing less miles with that fuel.

 

[l0rd]

That's b****cks.

What has happened, is you have increased the rolling radius of the wheel, which means to cover the same distance on the 16's, as you were covering on the 15's, requires less turning of the wheel. This tricks the odometer into thinking you've done less mileage, when in actual fact you haven't.

You'll still be using the same amount of fuel, but the computer will think you've been doing less miles with that fuel.

B******s^2

TBH changing the tyres on a car can make a difference on fuel consumption although you keep the same dimensions.

There are many reasons why changing from 15" to 16" can make a difference in fuel consumption.

Reasons

Tyre type
Tyre pressure
Tyre width
Friction
Rolling radius
Temperature

etc.....

As you can tell you missed as well quite a few.

 

[Dave..]

You aren't going to drop 7 miles of your driving to a gallon of fuel, just because of tyre friction, not unless you've got the brakes on as well!

 

[l0rd]

No, but when i changed my wheels on my car from 14" with Toyos to 15" but the tires where c**p i managed to increase my mpg.

All i say, is that there are quite a few variables than can affect consumption.

 

[mantis946]

I never did fully figure it out, it's consistent at 35 and I've had a fair few miles since the original post. I would agree with all of the above, the trip is probably reading it wrong and these alloys are pretty heavy so I can imagine a drop. I'm currently using £50 a week to do ~250 miles. I've also developed a club foot which wont help

 

[Stu_182]

That's b****cks.

What has happened, is you have increased the rolling radius of the wheel, which means to cover the same distance on the 16's, as you were covering on the 15's, requires less turning of the wheel. This tricks the odometer into thinking you've done less mileage, when in actual fact you haven't.

You'll still be using the same amount of fuel, but the computer will think you've been doing less miles with that fuel.

I agree with this. Tyre friction will be minimal difference to mpg also the op could be using 195s on the 16s.

 

[mantis946]

I was originally using 195 on the front and when they burnt out I swapped to the 205's so i've kinda checked both side's of the water. I'll be selling in not too long so I will get a set of 15's and see how it responds