2009-2011 Jetta & Golf MPG vs MPH and RPM

[Plus 3 Golfer]

There seems to be a thread every week or so of members concerned about their fuel economy (FE) being too low or not what they expected. Since we don't know their driving style, driving conditions, and so forth, about all we can say is that their FE seems too low compared to ours and maybe give a few examples of our average tank FE or perhaps some MFD MPG from interstate driving.

Nearly two years ago for about 3 months in AZ in Jan-Mar 2009, I kept track of my MPG vs MPH for shorter distances (3-10 miles) as shown in the graph below indicated by the blue diamonds. I have shared some of this data before in posts but believe it may be helpful to others to put it together in a graph (a picture is worth a 1000 words).

I've also included other data from Derrel H Green and Darth Furious for comparative purposes. If others have similar data, please PM me or list the data in this thread and I will try to incorporate it in the graph. Please include pertinent info like transmission, MY, additive used, tire pressure, mods and so forth. I realize this is not a scientific experiment, but if we can get enough data from manuals and DSGs by model, I think we can have more confidence in the data. Any comments would also be appreciated.

I'll make two comments on the data. First as you can see, Derrel has installed oversize tires on his JSW which give him about a 6% lower RPM over standard tires at the same speed. His effective gearing is now taller than the 2009 manual transmission Jettas (see graph). His tires are also fuel saving tires (low rolling resistance tires). IIRC, I've read somewhere that these tires can increase fuel economy by 1-3% (don't have cite maybe someone has better info?). Bottom line is that one might expect Derrel to achieve as much as 7-9% better fuel economy as equipped. When comparing Derrel's data with my data, Derrel is getting about 10% better FE at lower MPH with the % difference tailing off as the speed increases. This tailing off makes sense since drag force quadruples with a doubling of speed such that both sets of data should converge as speed increases.

Second, Darth Furious's data appears to be extremely out of range of what might be typical. Other posters in other threads also seem to have data in this range. Darth does have some mods in addition to the Revo tune.

This is the procedure I used in gathering my data:

1. Allowed my car to reach operating temperature (usually took about 7 miles @ 45 MPH for the temp gauge to reach 190*F). Even though the temp gauge showed 190*F, the oil temperature probably was still below operating temperature so I didn't start recording data for about another 5 miles or so.
2. Find stretches of highway of at least 3 miles that are fairly flat and where I could maintain a constant speed. This is fairly easy for me in the Valley of the Sun but I still checked my topo maps since I found a slight gain or decrease in elevation can significantly alter the data (eg. 50 feet/mile change can increase or decrease MPG by about 5 -10 MPG depending on speed).
3. Set cruise control at speed to be tested via GPS and zero out the MFD1 data to begin the test.
4. Record at least MPH and Average MPG from the MFD1 at the end of the run.
   It really helps to have another person in the car to record the data as the data can change quickly as one changes speed.
5. Repeat the test over the same route in the opposite direction. If the MPG difference between this run and the previous run was not within about 12 MPG, I didn't use the data. Either elevation change, DPF regen, or strong winds probably affecthed the data.
6. Average of the results at each tested speed. After accumulating data from about 10+ two way runs (ie, both directions), I did a simple average of the data. When I compared all two way runs, the data at a specific speed was within a 2 MPG bandwidth of the average. For example, if the simple average MPG was 50, the high two way pair was less than 52 and the low two way pair was greater than 48.

A couple notes: my data at 42k miles (blue dashed line) is very limited and only includes 2 two way runs (3-4 miles) at indicated speeds in the same day.
Does anyone know if the gearing for the 2011 Jetta TDIs is the same as 2010?

 

[Derrel H Green]

Good Post

There seems to be a thread every week or so of members concerned about their fuel economy (FE) being too low or not what they expected. Since we don't know their driving style, driving conditions, and so forth, about all we can say is that their FE seems too low compared to ours and maybe give a few examples of our average tank FE or perhaps some MFD MPG from interstate driving.

Nearly two years ago for about 3 months in AZ in Jan-Mar 2009, I kept track of my MPG vs MPH for shorter distances (3-10 miles) as shown in the graph below indicated by the blue diamonds. I have shared some of this data before in posts but believe it may be helpful to others to put it together in a graph (a picture is worth a 1000 words).

I've also included other data from Derrel H Green and Darth Furious for comparative purposes. If others have similar data, please PM me or list the data in this thread and I will try to incorporate it in the graph. Please include pertinent info like transmission, MY, additive used, tire pressure, mods and so forth. I realize this is not a scientific experiment, but if we can get enough data from manuals and DSGs by model, I think we can have more confidence in the data. Any comments would also be appreciated.

I'll make two comments on the data. First as you can see, Derrel has installed oversize tires on his JSW which give him about a 6% lower RPM over standard tires at the same speed. His effective gearing is now taller than the 2009 manual transmission Jettas (see graph). His tires are also fuel saving tires (low rolling resistance tires). IIRC, I've read somewhere that these tires can increase fuel economy by 1-3% (don't have cite maybe someone has better info?). Bottom line is that one might expect Derrel to achieve as much as 7-9% better fuel economy as equipped. When comparing Derrel's data with my data, Derrel is getting about 10% better FE at lower MPH with the % difference tailing off as the speed increases. This tailing off makes sense since drag force quadruples with a doubling of speed such that both sets of data should converge as speed increases.

Second, Darth Furious's data appears to be extremely out of range of what might be typical. Other posters in other threads also seem to have data in this range. Darth does have some mods in addition to the Revo tune.

This is the procedure I used in gathering my data:

1. Allowed my car to reach operating temperature (usually took about 7 miles @ 45 MPH for the temp gauge to reach 190*F). Even though the temp gauge showed 190*F, the oil temperature probably was still below operating temperature so I didn't start recording data for about another 5 miles or so.
2. Find stretches of highway of at least 3 miles that are fairly flat and where I could maintain a constant speed. This is fairly easy for me in the Valley of the Sun but I still checked my topo maps since I found a slight gain or decrease in elevation can significantly alter the data (eg. 50 feet/mile change can increase or decrease MPG by about 5 -10 MPG depending on speed).
3. Set cruise control at speed to be tested via GPS and zero out the MFD1 data to begin the test.
4. Record at least MPH and Average MPG from the MFD1 at the end of the run.
   It really helps to have another person in the car to record the data as the data can change quickly as one changes speed.
5. Repeat the test over the same route in the opposite direction. If the MPG difference between this run and the previous run was not within about 12 MPG, I didn't use the data. Either elevation change, DPF regen, or strong winds probably affected the data.
6. Average of the results at each tested speed. After accumulating data from about 10+ two way runs (IE, both directions), I did a simple average of the data. When I compared all two way runs, the data at a specific speed was within a 2 MPG bandwidth of the average. For example, if the simple average MPG was 50, the high two way pair was less than 52 and the low two way pair was greater than 48.

A couple notes: my data at 42k miles (blue dashed line) is very limited and only includes 2 two way runs (3-4 miles) at indicated speeds in the same day.
Does anyone know if the gearing for the 2011 Jetta TDIs is the same as 2010?

Thank you for your excellent post!

The respective gearings for both the 6 MT and the DSG transmissions are exactly
the same for both MYs 2010 and 2011 to the best of my knowledge.

There are really no reasons for VW to change the overall gearing of the 6 MTs.
They are already geared rather high, turning only 1663 RPMs per mile.
Many owners report not shifting into sixth speed until reaching 60 MPH or even higher!

However, I would like to see VW change the overall gear ratio of the DSG and make
that overall DSG ratio as close to that of the later 6 MT ratio as possible.

The way in which VW has the two transmission's overall gear ratios, the DSG and both
of the two 6 MTs arranged differently, gives both of the manual transmission cars
either a small or somewhat larger fuel economy advantage over the DSG!



D

 

[ruking]

42 mpg is about what I get ! The signature has some more information.

 

[glennco]

So, 6th gear on the MT is higher than the DSG. What kind of difference are we talking here?

 

[ruking]

So, 6th gear on the MT is higher than the DSG. What kind of difference are we talking here?

Do a search there are a few posts with graphic posts.

 

[Plus 3 Golfer]

So, 6th gear on the MT is higher than the DSG. What kind of difference are we talking here?

Yes, look at the graph in my first post. The solid green line is the DSG and the orange line is the 2010 manual.

At 65 MPH the engine turns at 2095 RPM with the DSG vs 1802 RPM with the manual transmission or 293 RPM less (14% lower than the DSG). Or you can say that in 6th gear the 2010 manual is geared taller / higher than the DSG by about 16% (293/1802).

You can do the same calculation for the DSG vs the 2009 manual (purple line in graph) and find that at 65 MPH the 2009 manual turns the engine 68 RPM less than the DSG. So, the 2009 manual in 6th gear is taller than the DSG by about 3.3% (68/2027).

One last calculation show the 2010 manual is about 12.5% taller than the 2009 manual transmission in 6th gear.

 

[Derrel H Green]

Overall Gear Ratios

So, 6th gear on the MT is higher than the DSG. What kind of difference are we talking here?

The overall gear ratio for all 2009-2011 CR TDIs with DSG is 2.3104

The overall gear ratio for the earlier CR TDI 6 MTs is 2.2356

The overall gear ratio for the later CR TDI 6 MTs is 1.9872

As you can see by the numbers, this is indeed significant.

I wish the DSGs were geared exactly the same as the later 6 MTs.

There is no reason for the DSGs to be revving so high when cruising on the highway.



D

 

[Darth_Furious]

Second, Darth Furious's data appears to be extremely out of range of what might be typical. Other posters in other threads also seem to have data in this range. Darth does have some mods in addition to the Revo tune.

Awesome post. I was interested in something like this in my thread but you really outdid yourself.
I have about 6K miles and I'm still breaking it in. It's been improving a couple of MPG lately. I have REVO, roof rack delete, blocked grill. I expect my graph to look more like yours as time goes on.

When I really try, I think I can get similar numbers in ideal situations, but in real world, it's less. Also I notice it's been much worse lately due to cold weather. I'll post new numbers when it warms up in the spring.

 

[Plus 3 Golfer]

glennco, here's the actual gear ratios for the DSG and manuals used to produce the RPM graphs. Gears 1-4 use final1 gear on output shaft one and gears 5, 6 and reverse use final2 gear on output shaft two. So, one can then compute the overal drive ratio by multiplying the the selected gear ratio times the appropriate final drive ratio. For example, 6th gear for the DSG is 0.76*3.04 = 2.3104 as Derrel indicates.

When my OE Bridgestones wear out (in about 10k miles), I will likely buy oversize tires like Derrel and enjoy the taller ratio and better MPG.

 

[Derrel H Green]

Raising the vehicle

When my OE Bridgestones wear out, I will likely buy oversize
tires like Derrel and enjoy the taller ratio and better MPG.

Changing the original sized tires, 205/55-16s to taller tires such as the 205/65-16s, the
diameter is increased from 24.9 inches to 26.5 inches, raising the vehicle .8 inches.

What does that do as far as creating additional wind resistance,
and how does that effect our F E?

Does raising the vehicle eight tenths of an inch change the drag coefficient?



D

 

[glennco]

That is a significant difference related to gearing, and it does help explain why the folks with manuals get significantly better hwy mpg.

I must admit this is really a great thread, great job pulling all this together from those other threads golfer, and thanks for all the great info golfer/derrel/all others.

I wonder if vw used such low gearing on the dsg to enable it to get into high gear asap. It also helps with power on the road, but given the torque curve of the TDI, I don't know why they'd be worried about that.

 

[crumptdi]

About the tire size increase: I put tires on my grand cherokee about 10% increase in road speed vs stock and despite the increased height I averaged about 10% higher mpg on highway. Yes it increases drag coef but in this case still was better mpg. Also don't forget to change tire size in the mfd otherwipe you won't see the gain. In the grand cherokee there is no way to change tire size and the mpg displayed did not change with the ride height. It was only when you factored in the 10% more distance traveled. With the tdi torque I doubt the slight drag increase would lower mpg. You would very likely gain 10% mpg for a 10% speed increase.

Also for speed increase were talking circumference so for example going from a tire with an overall height of 20in to a tire with an overall height of 21in you only add half inch height to your car but you gain about 10.25% distance traveled. That's a good trade off. Or just lower your car a little

 

[crumptdi]

http://www.net-comber.com/tirecalc.html

Just found this site for tire size calculations

 

[Plus 3 Golfer]

Actually, raising the ground clearance 0.8 inches with the GY Fuel Max 205x65x16 tires is probably good for me. I won't scrape as many of the concrete parking curbs with the underside of the front bumper cover. IIRC, the ground clearance on the 2009 is about 5.1 inches.

Here's a graph showing RPM VS speed for all gears. There's no question that the DSG will zip through the gears reaching a higher gear quickly. This should help fuel economy in lower speed driving like speeds under around 50 mph and in stop and go city driving.

As has been pointed out in other threads, 6th gear in the 2010 manuals is like an overdrive compared to the DSG and 2009 manuals. 5th gear in the 2010s is very close to 6th gear in the DSG and 2009 manual.

I did not plot curves using oversize tires with the DSG since adding more curves to a very busy chart would make it more difficult to read. However, one can see by dropping each DSG curve by 6% for the 205x65x16 oversize tires that for 1st gear - the DSG with oversize tires would be very close to the manual curves; for 2nd, 3rd and 4th gears - the DSG curve would be higher (or still shorter) than the 2009 manual; and for 5th and 6th gears - the DSG curve would be slightly lower (or now taller) than the 2009 manual.

 

[Darth_Furious]

Here's a graph showing RPM VS speed for all gears. There's no question that the DSG will zip through the gears reaching a higher gear quickly. This should help fuel economy in lower speed driving like speeds under around 50 mph and in stop and go city driving.

As has been pointed out in other threads, 6th gear in the 2010 manuals is like an overdrive compared to the DSG and 2009 manuals. 5th gear in the 2010s is very close to 6th gear in the DSG and 2009 manual.

WOW! This is an AWESOME resource!

 

[Rockwater]

PM'd with data for 2010 JSW 6 Speed manual.

 

[Plus 3 Golfer]

Thanks Rockwater for the 2010 JSW manual data. I've plotted it on the graph shown below.

For information, Rockwater's data was gathered when he had between about 1000 and 1500 miles on his car. It's readily apparent that the taller 6th gear of the 2010 manual improves fuel ecomony over my stock DSG at constant speeds. It's also interesting to note the the Rockwater's, Derrrel's and my curve converge as speed increase due to increasing drag.

 

[Rockwater]

I have pulled my post. Now if you will pull yours please.
That will make it less confusing, and also save space here.

Can you imagine what yours will do when it gets some more break-in mileage?
And what might happen if and when you might go to the same tires as I am running?

BTW, which wheels do you have? And your tires are . . ?
Not trying to be nosey. Hope you understand, but tires can and really do help also.



D

No problem between friends.

Part of the reason I ran the mpg trials soon after I bought the car was to have a baseline for assessing break-in effects when mileage became high enough. I'm sitting at about 26,xxx miles now so when spring rolls around and air temperatures warm to where they were during the first set of tests, I'll run them again. I actually tried doing this in late fall but ran into some bad weather during the tests which adversely affected the mpgs of some runs. Interesting set of data which I plan to post at a later date. I've also tested the car over a wide temperature range at a preselected constant speed and will post those mpg results when I have the time.

My car is all stock except for a dieselgeek skid plate. Tires are the original Hankook Optimos on 16-inch Bioline rims. Did you notice a change in mpgs when you switched tires? Can your MFD be reset for new tire sizes to preserve mph, mpg, etc. accuracy? Always wondered about that. Thanks.

 

[Derrel H Green]

Questions

Did you notice a change in mpgs when you switched tires?

Can your MFD be reset for new tire sizes to preserve mph, mpg, etc. accuracy?
Always wondered about that. Thanks.

First:

Yes, but that change was not readily readable at first glance.
Review my Fuelly entries being April 27, 2010. Perhaps you may see a pattern?
Our JSW was new, and not nearly broken it yet at approximately 4,400 miles.

Took some time before I was fully aware of what was actually happening.

GY says a four percent improvement in F E, and I think that is about right.
I am getting more than that, but how much of the increases I am seeing
are from the LRR GY tires and how much improvement in F E is from
going to a taller tire which decreased the RPMs?

Second:

Concerning the question about going to a bigger (or different) diameter tire and not being
able to have your MFD, Speedometer and Odometer be correct, VW has seen fit to
provide us with an adjustment. This adjustment must be done using a VAG-COM!
Very thoughtful and considerate of VW to provide such a feature, don't you think?

In my case, the DSG JSW was set from the factory with a '7'.
For it to be exactly the same as it was prior to changing tires, my friend, using his VAG-COM,
discovered that the adjustment needed to be changed from the stock setting of '7' to a '3'.

It now reads and shows everything accurately just as it did before I upsized the tires!

Questions and/or comments are welcomed.



D

 

[Oldbeaver]

TDI fuel economy graph

Great job! Thanks to share with us.


Thanks again.

Oldbeaver

 

[Plus 3 Golfer]

Great job! Thanks to share with us.

It would be greater if you explain a little bit the leyend of each graph for MPG vs MPH, as there are several leyend terms, such as 22k, 42k (sure they aren´t kilometers) difficult to interpret.

Best if you detail every one.

I suppose Plus 3 is some additive to the same preceeding setting?

Thanks again.

Oldbeaver

LOL, no Plus 3 in not an additive, it's the first part of my user name.

The 22k and so forth are miles not kilometers. I think I'll remove the blue dashed line as it adds confusion.

 

[oilhammer]

The overall gear ratio for all 2009-2011 CR TDIs with DSG is 2.3104

The overall gear ratio for the earlier CR TDI 6 MTs is 2.2356

The overall gear ratio for the later CR TDI 6 MTs is 1.9872

As you can see by the numbers, this is indeed significant.

I wish the DSGs were geared exactly the same as the later 6 MTs.

There is no reason for the DSGs to be revving so high when cruising on the highway.



D

Couple things about the DSG:

It will always need to be geared lower in some fashion for first gear, otherwise you'd be smoking the 1-3-5 clutch pack in traffic. There is no fluid coupling.

The clutches are held in place by hydraulic pressure, provided by a hydraulic pump, driven off of the engine. The faster the engine turns, the faster the ATF pump turns, the more available pressure is on hand. It may just be the engineers felt the torque load on the clutches at highway speeds in 6th gear meant that they needed XXX volume/pressure of ATF on hand, and therefore placed the gearing accordingly.

At what RPM will it shift into 5th? That is probably the very lowest RPM it can handle at light loads.

 

[Timpackman]

GREAT THREAD!

Makes it easier for me to pick the manual trans here next month.

 

[Derrel H Green]

At What RPM will it Shift into 5th

Couple things about the DSG:

It will always need to be geared lower in some fashion for first gear, otherwise
you'd be smoking the 1-3-5 clutch pack in traffic. There is no fluid coupling.

The clutches are held in place by hydraulic pressure, provided by a hydraulic pump,
driven off of the engine. The faster the engine turns, the faster the ATF pump
turns, the more available pressure is on hand. It may just be the engineers
felt the torque load on the clutches at highway speeds in 6th gear meant
that they needed XXX volume/pressure of ATF on hand,
and therefore placed the gearing accordingly.

At what RPM will it shift into 5th?
That is probably the very lowest RPM it can handle at light loads. [?]

Are you saying that an overall ratio of 13 to 1 is too high of a ratio when
starting out from rest for this transmission? I cannot believe that!
Many is the time that mine uses second gear to move when I am
not completely stopped, and everything seems to work just fine.

Indeed there's no T/Convertor as in a slush box, but the clutches are run wet, not run dry.

'At what RPM will it shift into 5th?'
Are you asking for the lowest upshift rpm from 4th into 5th or
when it would downshift from 6th gear back into 5th speed?



D

 

[oilhammer]

I am just giving you a basic outlay of how the transmission works, and a possibility as to why it is geared the way it is. First gear needs to be very low, so you can "creep" in traffic with the 1-3-5 clutch fully engaged. This is why the newer DSGs are 7 speeds (we don't have them here...yet).

I know what a wet-disk clutch pack is .

Sorry I offered any info.

 

[Derrel H Green]

Please Answer my Question

I am just giving you a basic outlay of how the transmission works, and a possibility as to why it is geared the way it is. First gear needs to be very low, so you can "creep" in traffic with the 1-3-5 clutch fully engaged. This is why the newer DSGs are 7 speeds (we don't have them here...yet).

I know what a wet-disk clutch pack is .

Sorry I offered any info.

Do know how the tranny works, as I have read everything that I could find on how it functions.

You did not, however, answer my pointed question directed to you?



D

 

[Rockwater]

Thanks Rockwater for the 2010 JSW manual data. I've plotted it on the graph shown below.

For information, Rockwater's data was gathered when he had between about 1000 and 1500 miles on his car. It's readily apparent that the taller 6th gear of the 2010 manual improves fuel ecomony over my stock DSG at constant speeds. It's also interesting to note the the Rockwater's, Derrrel's and my curve converge as speed increase due to increasing drag.

Plus 3,
In looking at the graph, all plots appear to be roughly parallel except yours which is flatter. Any idea why? Thanks

 

[Plus 3 Golfer]

Actually, I don't believe they should be parallel because the power to overcome drag goes up by the cube of the velocity. So, the power required to overcome drag at 100 mph vs 50 mph is 8 times more (100/50)^3 = 8. Maybe someone with more fluid dynamics / mechanical knowledge could offer / check my explanation below.

The power in Derrel's, yours, and my car is the same. The coefficient of drag is vitually the same. Derrel does have lower rolling resistance tires. As we continue to accelerate more and more power is used to overcome drag in fact 8x more at 100 mph than 50 mph. So, assuming that the other forces acting on our car are virtually linear with speed, the magnitude of the difference between our mpg at low speeds should not stay constant as we increase speed but should get smaller or converge. If all forces acting on the car were linear vs speed including drag, then the curves would tend to be parallel.

I don't know why Darth's curve is so low especially at higher mph. He does have the revo chip though. Last summer, in TX on I 10/20 where the speed limit is 80 mph, I ran at 85 mph for about 100 miles or so (both directions) with the A/C on, fully loaded car and got about 35 mpg on the MFD when running at 85 mph. At 85 mph, Darth's curve reads about 26/27 mpg. That's about 25% lower than what I got. That just seems way too low.

 

[Derrel H Green]

Darth's Modifications

I don't know why Darth's curve is so low especially at higher mph.
He does have the revo chip though.
Last summer, in TX on I 10/20 where the speed limit is 80 mph, I ran at 85 mph for about
100 miles or so (both directions) with the A/C on, fully loaded car and got about 35 mpg
on the MFD when running at 85 mph. At 85 mph, Darth's curve reads about 26/27 mpg.
That's about 25% lower than what I got. That just seems way too low.

Darth has done some other modifications also. See:

http://forums.tdiclub.com/showthread.php?t=297457

Not mentioned here are his 'Porto" 17 inch wheels which do not help F E.

Also, he's done some others modifications such as a mufflerectomy, removing
the factory roof rails, and raising the back slightly with rear spring spacers.
I'd do that last one if I knew for sure it would help F E even just a little bit.



D

 

[KB3MMX]

The taller overdrive in a manual trans would be nice but mandatory shifting blows for the small tradeoff of fuel economy.

A 7 speed US DSG would be nice... but a deeper overdrive 6th gear or taller final drive ratio with wider gearing.