So which petrol is really cheaper then

flashg67

[Deleted User] said:

I've been driving for 50-odd years, clocking up massive mileages, and have never once used Redex or any similar snake-oil product, nor bought any "super" petrol, even when the company was paying. Have I been going wrong?

Me neither in nearly 40 yrs of driving. Perhaps you could try the next 50 years using super petrol for comparison? Don't forget to post back with the results...

Goudy

Dr_Crypto said:

Are there even different grades of diesel? I’ve only ever seen the standard black nozzles and I too drive one! 

Yes, though the difference is it's cetane number or CN.

The higher the cetane number the shorter the ignition delay meaning it ignites quicker.
As there's no timed spark to ignite the fuel, it auto ignites under compression and the quicker this happens, the more complete burn you get out of the fuel, so you get more power and less emissions.
This quicker burn also reduces diesel knock a little.

Generally normal pump diesel is around 51 CN in the UK and Europe (EN 590)
Super diesel is at least a coupe of points above that, depending on who's selling it.

Cetane is adjusted by adding a hydrocarbon, usually in the form of a chemical called 2- EHN.
You'll find this in every pump diesel in varying amounts and nearly every diesel fuel treatment that you add to the fuel system but can be bought in bulk fairly cheaply as it can be used in home brew biodiesel production.

born_again

Mishomeister said:

Having found out that due to the recent changes to petrol I will now have to fill up my car with more expensive 'super octane' petrol I was jealous to many drivers that will not.  
But here is the observation that I made today:
Super unleaded cost 1.41 at Tescos. And the normal petrol costs 1.34 so 7p difference si roughly 5% difference.
But the new petrol is 10% less efficient meaning you will be able to drive 10% less distance with it?
Making it technically 5% more expensive that super unleaded?

I look at it like this.
EG:
E10 = £1.20 a LTR
E5 = £1.32 a LTR

That is a 10% difference in price. 
Say you get 10 miles per LTR with E10. To get the same VFM with E5 you would need to get 11 miles per LTR. So 4.5 miles more per gallon approx.
Never see that sort of return using super fuels. In either bike or car over many tanks.
I see better change of MPG in warmer weather than the change between std & super fuels.

As it stands at the moment. It will take a while before you can really say if E10 is making a difference due to mixing of fuels in garage tanks & car tanks.