Doing the maths ... which fuel is cheaper

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Charles
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Doing the maths ... which fuel is cheaper

Post by Charles » Wed Oct 06, 2021 6:58 pm

Just completed an interesting calculation when it comes to using E10 unleaded or E5 super unleaded in my car.

Over quite some mileage, I have established that I achieve about 25mpg when using normal Shell unleaded and 28mpg when using VPower. However, the new E10 is reported to cut economy by 10% so I would expect to get 23mpg on E10 fuel.

I did the sums using the following data:
E10; 23mpg, £1.42 per litre
Vpower; 28mpg; £1.52 per litre

In simple terms, cost per mile for each fuel is as follows:
E10 = (1.42 x 4.546)/23 = 28.1p per mile
VPower = (1.52 x 4.546)/28 = 24.7p per mile

As an extra, running the numbers at 25mpg for E10 = (1.42 x 4.546)/25 = 25.4p per mile, which means that even if I don't experience a drop in economy using E10, it is still cheaper to run VPower

As such, I can now fully justify buying the more expensive VPower over Shell's "ordinary" E10 fuel as it clearly costs me less per mile whilst at the same time giving me full performance.

Win Win, I think :dance
Charles
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Re: Doing the maths ... which fuel is cheaper

Post by hap » Wed Oct 06, 2021 8:54 pm

Great analysis Charles
I don’t have any local shell to me but presume similar saving on esso and Tesco super?

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Re: Doing the maths ... which fuel is cheaper

Post by Charles » Wed Oct 06, 2021 10:22 pm

hap wrote:
Wed Oct 06, 2021 8:54 pm
Great analysis Charles
I don’t have any local shell to me but presume similar saving on esso and Tesco super?
Apply different price per litre and mpg (as appropriate) and you can calculate your own numbers

For example, for Tesco use £1.32 and £1.42 with the same mpg figures and you get 23p per mile for 99 Momentum and 24-26p per mile for E10 unleaded.
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Re: Doing the maths ... which fuel is cheaper

Post by ---pete--- » Thu Oct 07, 2021 6:49 pm

Just out of interest Charles, have you compared this calculated mpg with the BMW readout mpg at any point of the hundreds of thousands of miles?

I'm just curious whether the onboard computer calculates within a reasonable tolerance or not.
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Re: Doing the maths ... which fuel is cheaper

Post by Bob » Thu Oct 07, 2021 8:09 pm

Based on a selection of cars I’ve owned (mix of new/older and brands) I’d say the obc is usually optimistic by at least a couple of mpg
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Re: Doing the maths ... which fuel is cheaper

Post by Charles » Thu Oct 07, 2021 9:09 pm

---pete--- wrote:
Thu Oct 07, 2021 6:49 pm
Just out of interest Charles, have you compared this calculated mpg with the BMW readout mpg at any point of the hundreds of thousands of miles?

I'm just curious whether the onboard computer calculates within a reasonable tolerance or not.
My mpg figures are based on full to full against mileage on the trip over quite a few miles and multiple fills. My OBC is currently showing just over 27mpg (long term) which is about 4% low against actual consumption over the same period.

Close enough in my book!
Charles
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Re: Doing the maths ... which fuel is cheaper

Post by Charles » Fri Oct 08, 2021 8:38 am

Just to add, I tend to have a rough calculation running in my head such that if I have driven about 330-340 miles since the last fill and I refuel shortly after the light comes on at 50 miles range to go, then I typically put in about 55 litres which means that I am getting about 27-28mpg.

Slightly different with the winter set on as it improves to about 360 miles and 30mpg.

Either way, it's generally there or thereabouts ...
Charles
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Re: Doing the maths ... which fuel is cheaper

Post by Jules Sunleu » Sat Oct 09, 2021 12:28 am

Great thread and totally agree Charles. Me and the Mrs use Super in our dailies too as better for the car and no more expensive for the reasons you have mentioned.
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