So I've not been particularly happy with my mpg since getting my 1.6 DSG estate. It has typically being doing between 45 and 47 on my commute and on a 550 mile round trip to Plymouth last month, it returned 49.02 - this is done using the brim to brim method and an Excel spreadsheet but largely agrees with the on board computer +/- 0.5mpg.

 

However, yesterday I did the exact same round trip of 550 miles to Plymouth and back, this time with my roof bars on, loaded with a 10ft paddleboard on the top and I got 57.19 !! That is a massive difference and I had the wind resistance of roof bars and a paddleboard. The onboard computer said 57.1 so again, very close.

 

Only 3 things have happened since my last round trip:

 

1. I ran some diesel fuel system cleaner through it

2. I changed the air filter

3. I removed my summer 17" alloys and replaced them with Goodyear Ultragrip 16 inch steel wheels.

 

I can't actually beleieve that any of those would account for so much difference, but I could beleive the each one my add up a little. Any thoughts? The car has now done nearly 27k. The air filter might have been the original, but it didn't look particularly dirty. The summer tyres I took off are Continentals, so a half decent brand. Tyre pressures are correct on both sets.

 

I'm a bit stumped really

 

Nick

Your figures seem a little low to me, even this latest figure of 57.1mpg. My regular commute is 90 miles daily, mainly motorway, and I've got used to putting in 20 litres at a time (to help keep track of MPG and also to be able to pay contactless, once you've added a couple of tasty snacks comes to just under £30). This usually gets me 270 miles or 3 days commute, and works out at about 60 mpg. I do stick to the speed limits but like to get to cruising speed as quickly as possible .

 

The only "mods" I've done are Pipercross Air filter and Pedal box - gets me to 60 quicker. How's your DPF - have you checked with VAG DPF and an ODBII  dongle?

Edited 6 March, 20197 yr by vRSWitter

@NikTheGeek

Did you take a tape measure and check the total circumference of the different tyres?

Maybe they are the difference between Ooo & Ahaa, but always best to measure and see.

The cold had a dramatic effect on my MPG in recent weeks. When it was chilly, even with the most delicate of driving, I was struggling to get anywhere close to my usual 55mpg average. It was hovering around 45mpg. Now the temperature is higher, I'm getting around 53.

 

There are loads of factors which affect MPG as you probably well know (weight in your car, temperature, tyre pressures, etc etc) so getting it bob on all of the time is truly difficult.

 

One thing just to bear in mind, as you're already doing, is your fuel / fuel additives. Some people think they're a load of **** and bull, but I use Shell V power diesel and very few months, I throw in a drop on redex as well.

 

Ah, temp would have played a part. Last month it was snowing so hard that the ACC cut out with a warning several times! Yesterday, it was quite mild. If temperature has that much of an impact, I'm looking forward to summer

Changing from 17" to 16" wheels could mean more revolutions for the same mileage travelled?

Maths isn't my strong point but wouldn't this mean the car thinks it has travelled further than it has?

Where is the input to the speedo/odometer taken from?

The wheel revolutions?

Drive shaft revolutions?

I only offer this as food for thought for a Briskodian who knows more about this than I do.

 

 

7 minutes ago, Stewart7 said:

Changing from 17" to 16" wheels could mean more revolutions for the same mileage travelled?

Maths isn't my strong point but wouldn't this mean the car thinks it has travelled further than it has?

Where is the input to the speedo/odometer taken from?

The wheel revolutions?

Drive shaft revolutions?

I only offer this as food for thought for a Briskodian who knows more about this than I do.

 

 

Depends on tyre size but if its one of the standard sizes it'll be near enough identical on the rolling circumference. 

33 minutes ago, Kenai said:

Depends on tyre size but if its one of the standard sizes it'll be near enough identical on the rolling circumference. 

 

This. The wheel might be smaller the tyre taller making up the difference.

I believe it will take more torque from the engine to turn the larger wheel. Even if the tyre/wheel circumference is more or less the same. I can’t remember all the science, but I’ve read about it, you’ve replaced some wheel material with rubber and air which is lighter, so easier for the engine to turn. If the 16”s are narrower then there’s also less friction.

My 1.4tsi has 16” tyres as standard and qualifies for £30 road tax due to lower emissions than the 17” wheel version of the same year, even though with lower profile tyres the circumference is about the same. 

The fuel cleaner and air filter will have helped as well.

I would have questioned the mileometer and trip computer readings being affected to give false mpg, but if you’ve done an identical journey and physically used less fuel, then it’s a fact your mpg improved.

Edited 6 March, 20197 yr by classic

Summer tyres were 17" alloys with a 225/45/R17 tyres on.

Winter tyres are 16" steel wheels with 205/55/R16 tyres on.

 

I gather they are as near identical a circumference as you can get 25" vs 24.9". Weight-wise, I've no idea, but surely the smaller steel wheels would be roughly the same as the larger alloy wheels since steel is heavier?

 

I'll have to do some more tests, but I don't have any long journeys planned for a while, so I'm driving my petrol MG TF for short trips.

 

Nick

3 hours ago, NikTheGeek said:

 

Ah, temp would have played a part. Last month it was snowing so hard that the ACC cut out with a warning several times! Yesterday, it was quite mild. If temperature has that much of an impact, I'm looking forward to summer

 

Just thought, why would temp play a part? I thought that cold air was more efficient due to its density and that was the whole point of cold air scoops and intercoolers!

Is it just engine temp and efficiency? Or does the whole cold air thing only apply to petrol engines? I probably should know this after years of owning cars

 

Maybe I'll have to get a radiator muff that I used to do with old Landrovers and try and keep the engine warm!

I think the cold air thing is that the colder air is more dense as you say. However, the advantage for an engine is that you can burn more fuel, for a given engine size, and therefore produce more power. It’s the fuel that provides the energy.

 

Edited 6 March, 20197 yr by classic

Thinking about it, if the air is denser, then the car will have to use more fuel to push through the air ! There’s so many variables. If I’ve read your posts correctly then your first journey was in snow, but on summer tyres, that may have had an adverse effect...

A few more thoughts. Make sure tyres are correct pressure (maybe even a little over for better economy). Turn off AC. Do you have stop/start, that saves fuel (though some think it's not good for the engine components longevity). Otherwise driving style makes big difference. According to spec you should be getting 70+mpg on motorway. We're you carrying a heavy load?

First journey was in the snow, but it wasn't sticking and it was on the M6/M5 with cruise set at 75 on the way down and 70 on the way back (once I'd read that the cameras are active even when the gantry's aren't lit up). It was on summer tyres with just 2 up and 1 overnight bag.

 

Second journey was monday/tuesday this week. Same sort of time of the evening, weather was much better, raining though. 2 in the car again and 1 case, but this time a 10ft paddleboard on the roof and the roof bars fitted. Winter tyres and cruise set at 70 both ways.

 

Both times the car was in eco mode with stop start enabled.

 

I really can't see a big difference just outside temp, tyres, fuel cleaner, air filter and the fact the car is new to me and maybe it's learning my driving style. If anything, I drove it harder on this second journey - at least when cruise wasn't on - ie on the minor roads. I drove it like I stole it. First time I was driving very sedately.

 

It's only had 2 long journeys since I've owned it. I'll have to do more experimentation I think. The summer tyres will be back on in a month or so I'd have thought and then we'll see if there's a change.

 

Nick

If you had a (or more) dpf regen(s) on the first journey that would also harm the mpg.

I think dpf  regens on modern diesels harm the overall average mpg. You can get good mpg on individual journeys but the dpf regens literally burn fuel.

Edited 6 March, 20197 yr by classic

End of March and Winter Spec Diesel & Petrol will not be getting delivered to filling stations in the UK, 

unless the buyers have a large supply bought up from refineries and bunkered and sitting offshore or in transit to the UK so might still be getting sold for a while longer.

8 hours ago, NikTheGeek said:

Summer tyres were 17" alloys with a 225/45/R17 tyres on.

Winter tyres are 16" steel wheels with 205/55/R16 tyres on.

 

I gather they are as near identical a circumference as you can get 25" vs 24.9". Weight-wise, I've no idea, but surely the smaller steel wheels would be roughly the same as the larger alloy wheels since steel is heavier?

 

I'll have to do some more tests, but I don't have any long journeys planned for a while, so I'm driving my petrol MG TF for short trips.

 

Nick

Unsprung weight of the wheels has an enormous effect, I guess the steels are between 1-1/2 to 2 Kg lighter per wheel

 

That's where the difference is

 

8 hours ago, NikTheGeek said:

Summer tyres were 17" alloys with a 225/45/R17 tyres on.

Winter tyres are 16" steel wheels with 205/55/R16 tyres on.

 

I gather they are as near identical a circumference as you can get 25" vs 24.9". Weight-wise, I've no idea, but surely the smaller steel wheels would be roughly the same as the larger alloy wheels since steel is heavier?

 

I'll have to do some more tests, but I don't have any long journeys planned for a while, so I'm driving my petrol MG TF for short trips.

 

Nick

I think you may surprised and find the alloy is heavier. On a previous car a 16” alloy weighed a lot more than a 16” steel.

Edited 7 March, 20197 yr by cheezemonkhai

I was told that the reason for me paying £20 road tax instead of £0 that other cars pay is the the 17" alloys. So maybe it is that. I'll keep benchmarking the mpg and if I see a sudden drop when putting the summers back on, then the 17" alloys will be going and I'll get some 16" alloys instead.

Save the money and use it on fuel. If a first long journey was poor, it could be the car had the average including a lead footed previous driver in.

 

Tank to tank will be affected by dog regeneration cold, different wheels etc.

 

maybe only 1 to 2 mpg each but enough to add up.

 

when I changed afriends air filter that was old and dirty, but no worse looking than a 60k mike vag one, they gained about 10mpg.

 

Personally I would just keep an eye going forward.

 

in real world I found the 1.6 didn’t fare any better than the 2.0 and was actually worse on drives with inclines. Yes two cars and usually two drivers, but it gives an idea.

Two comments a 205mm wide tyre has 20mm less aero drag on each side of the car as it slices through the air, improving fuel consumption. Second a colleague has recently changed from an auto Citigo to a 16 plate SEL Octavia 2.0Tdi DSG Estate. He seems pleased to be getting 440 miles per tank but this is only 40mpg.

5 hours ago, shyVRS245 said:

Two comments a 205mm wide tyre has 20mm less aero drag on each side of the car as it slices through the air, improving fuel consumption. Second a colleague has recently changed from an auto Citigo to a 16 plate SEL Octavia 2.0Tdi DSG Estate. He seems pleased to be getting 440 miles per tank but this is only 40mpg.

Most people fill well before empty

Just a followup to this old thread of mine:

 

It's now warmer, I'm on summer tyres and my long term average for typical A road journeys around South Devon and Cornwall is 58.2mpg so I'm quite happy with that. It must have been the colder weather and/or winter diesel that affected the previous mpg. I can do better than 58.2 on the motorway, but 58.2 is my average.

 

Nick