MPG Vs. Wheel/Tyre Size

supermanjo

Question.

Which would be more economical:

15" alloy with 205/55r-15

or

17" alloy with 205/40r-17

I know the smaller the width of a tyre means more MPG due to lower rolling resistance, but what about the height of the tyre and the size of the alloy?

Bonus question:

16” alloy with 205/50r-16 -or- 205/60r-16

Thanks!

Notmyrealname

What is the circumference of each? If the circumference is the same, then the wider one will use more fuel than the narrow one. If the circumferences are different, the larger one will use more fuel when accelerating.

supermanjo

All the infomation is in the original post.

But to get to your point, are you saying it dosn't matter what the size of the alloy/tyre is - becuase the circumference is the only thing that counts? (same widths.)

laidbackgjr

Well all the combinations in the post are the same width, so that shouldn't be a factor. You will have slightly different circumference's which could impact gearing and therefore MPG, but whether they improve or worsen will depend to a certain extent on the car and it's existing gear ratio's.

To be honest you are probably talking about differences of around 0.1MPG, things like tyre pressure, brand of tyre would be just as significant factors.

Lum

Agreed the difference is tiny.

The weight difference between different types of wheels is more likely to make a difference, but even then we're talking a smaller difference than just emptying your boot of unnecessary crap.

Notmyrealname

supermanjo wrote: »

All the infomation is in the original post.

Can't be bothered to do the maths TBH

But to get to your point, are you saying it dosn't matter what the size of the alloy/tyre is - becuase the circumference is the only thing that counts? (same widths.)

Yes. The circumference is what counts as the forces, both resistive and drive, are ultimately exerted on the outer surface of the wheel.

mikey72

The circumference will only affect the gearing.
That outcome be positive or negative.

thefishdude

i agree weight differnece is the key the smaller tyres wiull be more economical.

bigger tyres and wheels weigh more, and if circumference is bigger tae more power to get moving also .

mikey72

thefishdude wrote: »

i agree weight differnece is the key the smaller tyres wiull be more economical.

bigger tyres and wheels weigh more, and if circumference is bigger tae more power to get moving also .

But inertia will them keep it moving whereas with a small tyre you will have to apply more power.

vikingaero

mikey72 wrote: »

But inertia will them keep it moving whereas with a small tyre you will have to apply more power.

Then the type of driving affects MPG - constant urban stop/start commute v. motorways.

mikey72

I the main effect on the economy would be the price of the tyres initially.