Why does DSG give reduced MPG?

[EdmundBlackadder]

So from an engineering point of view the DSG gives poorer MPG than a manual gearbox as though it changes gear at the optimum point the actual mechanics are less efficient and that outweighs any savings made at the changing point. Have I summed that up correctly?

If I have then why do cars like the Prius have an automatic gearbox when they are all about getting good mpg?

[lol-lol]

Can anyone answer why the MPG seems to go down when cruise is selected?

Best consumption is oftern achieved on a steady "throttle" position. To accelerate or ask for more power you usually have to richen up the fuel mixture to getting the engine to turn faster and get in more air.

Things have changed hugely in the last few years with Direct injection and turbochargers on nearly all VW group cars and hence fuel metering is improved hugely.

Criuse control does look to maintain speed without regard to fuel consumption. Best, but very boring, fuel consumption, is often where the turbo starts to give maximum torque. On my 1.8 TSI DSG that is 1500 rpm which equates to 43 mph in 7th gear, avery boring place.

Aerodynamic resistance, which is nearly always the most significant of the 3 restraining forces, the others being rolling resistance and the occasional change of height factor, is a cube rule ie to go a 100 mph takes 8 times more power to go at 50 mph.

If I am on the phone, GSM 2 through the car for safety sake, I often tuck in with the lorries who are on criuse at 54 mph, I will often emerge from a call with the fuel consumption having been in the 50s mpg, not bad for a car that does 0-62 in 7.8 seconds and 140 mph top wack!

I tend to only use criuse going through road work speed restrictions where I do find it useful.

Edited 25 August, 2011 by lol

[rockhopper]

So from an engineering point of view the DSG gives poorer MPG than a manual gearbox as though it changes gear at the optimum point the actual mechanics are less efficient and that outweighs any savings made at the changing point. Have I summed that up correctly?

If I have then why do cars like the Prius have an automatic gearbox when they are all about getting good mpg?

I saw an article a while back that took a prius and a 520d on a journey, and the manual 520d gave better fuel consumption. Admittedly it was over a reasonable distance and not much through towns....

Very difficult to have a manual gearbox with an electric motor and a petrol engine as the driving force. Don't they have an electric motor driving one end and a petrol engine the other, or is that the RX400/450h

[EdmundBlackadder]

Rockhopper - good point about the mix of electric and petrol engine. Forget that example.

[900000]

Don't they have an electric motor driving one end and a petrol engine the other, or is that the RX400/450h

No. All hybrids have the electric motor supplement the PETROL engine which then powers the driven wheels be they front, rear or both. (Apart from the Chev Volt / Vauxhall Ampera which has the electric power straight to the front wheels and has a range extender petrol engine that works as a generator only to top up the batteries when required).

Only recently did Peugeot launch their DIESEL Hybrid which has the diesel powering the front wheels and the electric motor the rear giving a sort of 4x4 system. This is in the 3008 and soon in the 508 Estate's "Scout" version. These are also the very first time you get diesel and electric mixed as normally the weight and cost penalty of a diesel with that of the hybrid batteries is just too much to make work in terms of weight and cost! But just imagine going off roading in one and then depleting the battery rendering your 4x4 stranded as it is now 2wd only! Doh.

[yellowyeller]

<snip>

I tend to only use criuse going through road work speed restrictions where I do find it useful.

Yep, me too.

In 50 MPH average speed restricted areas I reckon the speedo is 10% conservative and the police will tolerate up to +10% above the limit.

Allowing for some wiggle room I set the cruise at 57 MPH and sail through!

(apologies if somewhat off topic)

[BossFox]

Yep, me too.

In 50 MPH average speed restricted areas I reckon the speedo is 10% conservative and the police will tolerate up to +10% above the limit.

Allowing for some wiggle room I set the cruise at 57 MPH and sail through!

(apologies if somewhat off topic)

Why post off topic if it's just to say you speed where safety restrictions are in place?

FYI most speedos over read by 4 or 5 %.

[Little-Brit]

This thread is about the difference in fuel consumption between manual and DSG cars of the same model and specifically Yetis. The difference between a Yeti and more aerodynamic cars is really not relevant in this discussion...

[Little-Brit]

I have had my 1.2 TSi DSG for 8 months now and have covered 7,000 miles - loosening up nicely now!

Firstly I have to say that the fuel consumption varies more dramatically with driving style on the Yeti than with any previous car that I can remember.

On my daily commute, a 25 mile round trip of mixed town and rural driving (no dual carriageways), I have been getting between 35 and 40 mpg according to the on-board computer. This has been driving the car in D and at mildly enthusiastic but legal speeds.

As I have become accustomed to the car I have become a little frustrated by the DSG's desire to change up a gear ridiculously early - sometimes before 1,500 rpm. It is also a little reluctant to change down a gear when negotiating gradients and bends.

Consequently for the past few weeks I have taken to driving the car in "manual" mode all of the time. In so doing I rarely change up before 2000 rpm and often use 3000 rpm or more. I also change down in anticipation of hills and corners and consequently get a much more consistent level of urge when using the throttle.

And the result of this? Fuel consumption showing 42 to 49 mpg on the read out!

My conclusion is that the settings for the transmission are intended to produce low CO2 in the Euro test - not low fuel consumption in the real world...

[yellowyeller]

Why post off topic if it's just to say you speed where safety restrictions are in place?

FYI most speedos over read by 4 or 5 %.

For the same reason you just did, I was picking up on a point made by a previous poster.

Since ALL speed limits are for safety reasons, do I take it that you don't ever drive your Audi TT or "rather brisk" Fabia VRS above the limit? Presumably you regard driving 75 - 80 MPH on the motorway as excessive?

[BossFox]

For the same reason you just did, I was picking up on a point made by a previous poster.

Since ALL speed limits are for safety reasons, do I take it that you don't ever drive your Audi TT or "rather brisk" Fabia VRS above the limit? Presumably you regard driving 75 - 80 MPH on the motorway as excessive?

My daily car is a Greenline II and I drive everywhere at 60mph getting 78mpg...

I take a toy to a track when I want to go fast.

[freedie]

Fight!

[yellowyeller]

Fight!

Naah... I'm a pacifist...

I just hope I'm not on my bike when BossFox is doing 60 in a built up area.

Edited 27 August, 2011 by yellowyeller

[freedie]

Sorry. I should have added a smiley. What sort? I know not.

[Peter a Proud Yorkshireman]

My daily car is a Greenline II and I drive everywhere at 60mph getting 78mpg...

I take a toy to a track when I want to go fast.

Bet you hog the middle lane on the motorway Essex girl!!! Spend all your time looking at the maxidot when you should be looking at the road

I had a scalextric when I were a lad. Up here men are men and not southern softies trying to impress their bimbos!!

[BossFox]

Bet you hog the middle lane on the motorway Essex girl!!! Spend all your time looking at the maxidot when you should be looking at the road

I had a scalextric when I were a lad. Up here men are men and not southern softies trying to impress their bimbos!!

I happen to run a transport company, so I know the rules of the road rather well. :p

You'll find me in lane 1 most of the time unless someone is holding me up. Which is where all divers should be IMO.

I'll ignore the rest of your odd comments. :p

[Peter a Proud Yorkshireman]

Nowt odd about my comments just trying to wind you up!!! Always in the been good at fishing and you bit.

No sense of humour down there in the ratrace that is darn sarth? Quality of life is great up here is Gods own county!!!

Chill

PS I dont have to brag about my life acheivements I have been there and done it rather well.

[BossFox]

Nowt odd about my comments just trying to wind you up!!! Always in the been good at fishing and you bit.

No sense of humour down there in the ratrace that is darn sarth? Quality of life is great up here is Gods own county!!!

Chill

PS I dont have to brag about my life acheivements I have been there and done it rather well.

If I bit the post would have been much longer, rather than stating I was ignoring.

PS. Bragging would be saying how many staff, turnover or number of vehicles. It could just be me driving a van.

Not bragging, showing why I know which lane to drive in. Thought it was simple personally.

Now if I wanted to be silly and snipe back I'd ask if spelling was one of those achievements. But I'm not. So I'll bid you goodnight.

I don't come on here for silly wind ups generally, it's because I am a Skoda enthusiast. To talk to like minded enthusiasts.

I just don't recommend people posting that they break the law on a public forum.

Now back to the topic about DSG and fuel consumption...

[Peter a Proud Yorkshireman]

Peace Man ..... have a nice day :sun:

[cjb]

A few things about DSG: while it's good, it won't always be in the right gear- less often than a good driver with a manual. Plus, it's heavier than a manual, so some of the time it is bound to give worse MPG than a 6 speed manual. However, as someone mentioned, it has less losses than a epicyclic/torque converter auto, so it's better than one of those.

Edit: as far as MPG, In heavy traffic or with your foot down, about 39-40mpg. 55 mpg if very gentle, anywhere in between otherwise. The Fabia vRS I had before did 2-3 mpg better on average.

[Fred_Bristol]

My target is 40 mpg (often achieving 42 mpg) with my 1.2 TSI DSG and I'm dissapointed if it drops below 38 mpg. But what surprised me was the decrease in mpg when I changed from winter tyres to summer tyres.

And the consumption calculations took into account the error in mileage recorded due to the smaller rolling radius of the winter tyre. Perhaps there is something in Michelin's claim that its tyres are "Greener".

[lol-lol]

My target is 40 mpg (often achieving 42 mpg) with my 1.2 TSI DSG and I'm dissapointed if it drops below 38 mpg. But what surprised me was the decrease in mpg when I changed from winter tyres to summer tyres.

And the consumption calculations took into account the error in mileage recorded due to the smaller rolling radius of the winter tyre. Perhaps there is something in Michelin's claim that its tyres are "Greener".

Wider tyres use more fuel because of tyre hysteresis, wider the tyre the more hysteresis loss. Michelin generally have a lower loss through hysteresis than other manufacturers due to the use of advance materials hence (wider) summer tyre use more energy than winter ones.

Yeti seems to do about 5 mpg less than the Octavia for the same engine, ouch.

Horse for courses.

[lol-lol]

A few things about DSG: while it's good, it won't always be in the right gear- less often than a good driver with a manual. Plus, it's heavier than a manual, so some of the time it is bound to give worse MPG than a 6 speed manual. However, as someone mentioned, it has less losses than a epicyclic/torque converter auto, so it's better than one of those.

Edit: as far as MPG, In heavy traffic or with your foot down, about 39-40mpg. 55 mpg if very gentle, anywhere in between otherwise. The Fabia vRS I had before did 2-3 mpg better on average.

DSG gear selection is not as good as human brain. If you can see a down hill coming you can change up either in the manual or dsg. DSG will only change back down if it senses that the engine is struggling. I use the manual tipronic and paddles much of the time on my 7 speed DSG, and slip in to neutral and this can add a couple of mpg to the overall figure.