Hello can anyone help me with adjusting the mpg calculation on MK3 Octavia 2020? I've fitted larger wheels which I believe the car is going slower than it thinks affecting the readout on instrument panel.

Edited 8 November, 20241 yr by Blue8793841

So, less than 1%.

 

Don't forget that the larger wheels/tyres will also increase you fuel consumption.

 

Thanks. AG Falco

Use an app on your phone / gps and compare to the cars milometer and how far the car says you have travelled.  (yes i know about ups and downs, elevation change.)

 

As it is if you reset the Miles travelled, and compare with the miles showing on the cars total miles it can be a difference of tenths of miles that they show. 

usually, speedometers show 3-5% less than reality,
with +1% tires you have moved just little bit closer to GPS calculated values

 

for info about Fine Tune, search "Wheel circumference" in this thread
-> https://www.briskoda.net/forums/topic/516414-vcds-options-on-superb-iiifl/

 

^^^ That is Speedometers.   As required by legislation.  They can not under read.

 

It is distance that matters as far as fuel,

and that is not 3-5 % wrong with the OEM tyres, new or worn is it.     But really as it is Average MPG is not that accurate or exact anyway. 

ETA: just beaten to putting some of below.

 

You will need to do this a number of times over a reasonable distance and average it out, preferably over the same route with the same circumstances and environment but you are already in the car manufacturers' nth degree of nth degree of mpg figures which will vary on future tests.  The tyre figures you have shown are nominal and comparing new to new tyres of the same sort which I doubt was how you changed your tyres.

 

There are websites that give information to show how complicated this sort of thing is and at 1% change I'd guess you'd be within margins of error and variance.

 

Good luck though, let us know how you get on and the out come.

 

Edited 9 November, 20241 yr by nta16
ETA:

Thanks for the replies, the fuel economy seems miles off from what it was on the old wheels, say 10 mpg on my commute to work.

That is a lot.   But we have no idea the length of your commute to work.   Not much colder is it where you are? 

 

Then you have more rubber on the road, we have no idea what tyres you have on and if any less efficient.  More grip / traction / friction. SAFER.

 

You now have winter formulation petrol in the filling station, less hygroscopic than earlier in October, but no less of an octane / ron than before.

Still E5 or E10 if you use that.  It can actually be a higher ron then the Min 97 or 99 if you use Super Unleaded.

I appreciate the climate is a lot colder recently getting into single digits in the north east. I always use the vpower, ultimate fuels etc. Think I'm going to put the old wheels back on next week and see what happens.

How far is your commute, and have you brimmed your tank to be sure of your actual miles per litre.

& does your milometer show the same miles to work?

 

Can you do your car / engine a favour and use Tesco Momentum 99 ?, lovely stuff in the North East of England.

Shell V-Power is the same base fuel, just a different additive package and more expensive. Not superior. 

Edited 9 November, 20241 yr by Ootohere

I usually use the Esso premium stuff, I'll try Tesco see how that is. Keep tank between 1/2 and 1/4 as I don't do many miles maybe 5 to work. I'll also check on the miles to work too.

Esso where you are is delivered by Greenergy who produce Momentum 99.

 

Esso Synergy + 99 up north is not Zero Ethanol as in some areas of the UK. 

 

TSI,s (Turbos love Ethanol, but it is Hygroscopic so less is in petrol in winter in the UK.)

 

EDIT.

Maybe in the North East they have it 0% Ethanol, and from a different depot, not from Greenergy.

 

 

 

 

E5 will meet the Minimum Octane it is sold at, but that does not mean all around the UK the same Super Unleaded is the same, 

it can have a higher octane / ron than the Minimum it has to be. 

 

 

 

Edited 9 November, 20241 yr by Ootohere

21 hours ago, Blue8793841 said:

I appreciate the climate is a lot colder recently

 

21 hours ago, Blue8793841 said:

I don't do many miles maybe 5 to work

With short journeys and the colder weather it makes any mpg comparison pretty meaningless as the engine will spend a much longer time in warm up phase when consumption is higher.

When it is a bit colder even a TSI might just get to an indicated 92*oC Oil Temperature even if it uses 0w 20 FS IV. 

The difference of starting with a 10*oC lower ambient temperature so oil temp will affect MPG if just up to an efficient temp by the time you are stopping. 

My wife's 2015 1.2 TSI gets to 92c within about 7-8 miles on a journey of town and open country roads with 30, 40 and 60 mph roads but probably 50 mph over a short distance as the top speed.  Normally runs about 95/6c.  All according to the car's oil temperature dash multidot read out, usually on Dealership (bills) 0w-30, 5w-30 (5w-40 for indy garage), I've not checked with the better quality 5w-30 oil I put in.  But of course there are many variables especially comparing two different vehicles with two different drivers using in two different parts of the country.

 

The about 10 miles a gallon difference also depends on how that, and previous figures, were measured and calculated.

 

For the sake of conformation putting the old wheels back on will help, perhaps the 18" wheels and 40 profile tyres have rattled the car's computer brains.

 

Just an update, I have put the original wheels back on the vehicle and mpg has improved but not as much as I hoped. Must put it down the the freezing weather at the minute. I have seen a few misfires looking at live data but I don't know if this is normal on a cold engine.

17 hours ago, Blue8793841 said:

I have seen a few misfires looking at live data but I don't know if this is normal on a cold engine.

I'm not a mechanic or expert in anything but to me that would be a sign something isn't right, all the annoying computer programs, modules and sensors should prevent such things but does your engine have that active cylinders thing (shuts of cylinders to save fuel/emissions(?) as that may be too "clever" for the computer programs and real world physics.

 

Modern services are very skimpy basically just an engine oil and filter change (and only adequate oil IMO, I use better oil than the Dealerships/garages/mechanics even on this VW car) and a general look-see for chargeable work.  You need to make sure the scheduled "maintenance" is carried out in a timely fashion often by time rather than mileage intervals.

 

So at 4 years old have you had the spark plugs changed and engine air filter changed (cleaning the box and hoses I'd not expect from a paid person), depending on your location and driving environments I think the air filter change schedule might be too long in intervals (unless it's changed?).

 

Increased mpg is often a sign something is wrong (I think this was mentioned earlier by someone) there are of course many things that could cause this instead of as well as the engine which is why whole car servicing, maintenance and checks as required are important.

 

Scan tools are very useful and often very needed on modern cars but they are only one diagnostic tool another is the senses of the driver and mechanic, along with perhaps other diagnostic tools, don't just rely on sexy tools like scan tools but they could be very useful to help resolve this higher mpg if the cause isn't from other than the car.  Colder weather and you may be using more of the many facilities available on a 2020 car that use more fuel (and battery power, with your short journeys a preventative recharge using an appropriate battery charger maintainer, following the instructions in the 'Owner's Manual' and charger instruction booklet may be required to avoid issues and being a part of the season's call out statistics. 

 

5 miles is a short journey, I did check the oil temperature on my wife's car for this thread but forgot to report it back and have forgotten the details now but I do remember the temperature was lower than previously for the journey, whether this was because of the colder weather, different engine oil used, my poor memory or a permutation or combination of all three I don't know.  My wife told me mpg seemed reasonable on a three consecutive days run on back roads and motorways to NEC and back the other week, speed not above 60 mph.

 

A change in circumstances and use can obviously affect mpg, started towing a boat, carrying heavy passengers or other load, faults on brakes, etc, etc..

 

For this forum a full scan report or live data would be appropriate otherwise more generally the relevant Octavia forum might be appropriate for more reading and advice.

 

I don't think the difference in diameter/circumference between the two tyre sizes is going to make a 10mpg difference.

There are so many variables that could impact the MPG, it's beyond me to point to what the problem is, before looking at the possibility of a problem with the car.

Tyre pressures, fuel, temperature, tyre rolling resistance, wheel weight etc.

But 10mpg down certainly sounds like a problem to me.

44 minutes ago, EnterName said:

But 10mpg down certainly sounds like a problem to me.

That is about the difference between the best 64.8 MPG and the worse 55.6 MPG my Fabia has done this year.

 

 

Thanks. AG Falco

Like all figures it depends on what they relate to, 10mpg difference could be a lot or a little, I'm sure with many cars and owners if I drove their cars I could increase the mpg and with others decrease the mpg in the same journeys and weather, I'd not be very constituent driving my wife's car unless I really tried to be which would require a regulated route and type of driving in similar conditions.  Decades back, before the A14 fully opened I could use it to test my settings of servicing the car and adjusting the carbs when required (well as much as I was any good at doing that) and later 50mph at different times on the M1. M6 and A45.  I was going to a 100 mile test run on the M6 one time but my wife wanted me to speed up so I cut it to 50 miles, only cruise control was my right foot and keeping an eye on the rev counter needle (in 4th gear for direct and roof down).  Later in the journey after measurement I followed a couple of mates in their bigger, faster, more powerful cars at a higher speed and halved the mpg figure.

 

I want my mph accuracy to the 00.1 anything less does not comply 

@Skodacrazy Does not comply to what?  

Do you want that with brand new tyres and worn tyres and the tyres at a certain pressure? 

4 minutes ago, Ootohere said:

@Skodacrazy Does not comply to what?  

Do you want that with brand new tyres and worn tyres and the tyres at a certain pressure? 

sorry it was a joke haha 

 

that said 

 

I currently have rapid 2014 elegance spec alloys with 215/45/16 tyres

 

which size tyres can i fit to this alloy that give a more comfortable drive 

 

I’m just going to purchase 4 new 

 

@Ootohere 

Edited 15 December, 20241 yr by Skodacrazy

I posted in your other post.

 

What is fitted now, brand, speed/ load rating, are they XL tyres.

 

A size change might not be more comfortable, depends that they are in the size.

Then as far as safety you might fit a tyre with more grip / friction / traction and be less economical but be more surefooted, safety over economy. 

 

The guides are not always accurate when you put a tape measure around different tyre types / brands / tread depths.