Virtually no difference at all due to different profiles.

Can you elaborate on this, I would be sure that a lower profile tyre would give even worse MPG not better. Due to having a stiffer sidewall? Or is a stiff sidewall bad for MPG?

Then on top you have the thinner tyre giving less rolling resistance.

I know the fuel saving A2 had thin wheels and I think the fuels saving Polos are the same.

Having said all that perhaps 5-10% is too much to attribute to this.

Edited 19 November, 201213 yr by Dunkuk

Quite a good video example of using skinny tyres to improve MPG

This is quite interesting

Specification Sidewall Radius Diameter Circumference Revs/Mile Difference

185/60-14 4.4in 11.4in 22.7in 71.4in 887 0.0%

165/70-13 4.5in 11.0in 22.1in 69.4in 913 -2.8%

This adds to the confusion as if you are running the 185 width you will do 2.8% more miles per gallon if you take the mile reading from the Odometer / trip computer and not GPS!

One thing I thought about is that some cars have 165mm wide tyres and some have 185mm wide tyres. I would imagine this might make 5-10% difference

Virtually no difference at all due to different profiles.

Virtually no difference in rolling radius. However, for fuel consumption there can be a difference, as each tyre (i.e. each contact patch) is 20mm wider, so 80mm more contact across the whole car will increase the rolling resistance.

1.9 sdi fabia estate 2003 - 50mpg driving with a lead foot, 66mpg when playing it cool.

The speedometer drive is taken off the transmission to the front wheels, so by fitting skinny tyres to the rear wheels is only creating less drag, I hate to think what the ride quality is if the skinny tyres are inflated to their rated 60 PSI.

Or am I missing something !!

DB.

I am taking about the width of the tyres not the difference in circumference. If you cycle you will know all about how different tyres and pressures feel, you really notice it!

As an experiment I increased my tyre pressures and it made an immediate difference to mpg. But yes, 45psi at the front was quite hard, trying 40 at the moment, will probably end up a bit lower.

I think the greenline Fabia has high pressures, just trying to find out what they are at the moment.

Edited 23 November, 201213 yr by Dunkuk

Well the new fabia sdi hatch I bought has just beeped for fuel for the first time after it first tank full has been used. 482 miles to the beep. I can live with that. Thats running about a third SVO. For the current tank that I've just put in its a third again but also has just over a litre of petrol in it too.

I read on another forum that I should put the petrol into the oil and leave it for a month to 'do its stuff' before putting it in the tank. Is there any truth in that or is a good slosh round in the drum good enough?