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Comments
I'm not sure which forum the theory that more gears is always better was debated, and I don't want to play mechanical engineer myself, but after discussing this matter with friends who are mechanical and nuclear engineers, the "more is always better" theory was debunked, at least to my satisfaction. That's not to say that in a particular application (or even the majority of applications) an 8 speed might not produce better mpg than a 6 speed. But that is definitely not an absolute certainty and depends upon a number of factors.
Essentially, the trade off is how many gears are required to keep the engine rpms in the optimal range for fuel efficiency vs. how much energy is lost in shifting between gears. In most gasoline engines, the most efficient rpm range is relatively narrow. In diesel engines, because the torque band is wider, the efficiency band is a bit wider.
As you indicate, it is virtually impossible to compare apples to apples between a 6 and 8 speed. Even year over year comparisons when transmissions are changed is not fair, because transmission technology has vastly improved to reduce energy loss in the shifting process and drive train losses due to inefficient torque converters. Back in my old days, it was not uncommon for a 4 speed manual transmission to get 15%+ better gas mileage than a 4 speed automatic. Now the automatics often get better than their manual counterparts (Porsche 7 speed PDK vs. 7 speed manual).
One of the guys in this little golf course discussion group had an old 5-speed manual Toyota pick up truck that he put 240k miles on before finally buying a BMW 535i 6-speed manual in July. He commented that it's nice to have a good first gear now. Apparently, the Toyota's first gear was really only a "get rolling" gear ratio that practically redlined at 8 mph. He hardly ever used it in urban driving, preferring to start out in 2nd. And he claimed that that produced noticably better city mpg compared to shifting in and out of 1st gear at every stop sign or traffic light. For him, the Toyota would have been better off with a 4 speed manual, having a 1st gear ratio halfway between it's 5 speed 1st and 2nd.
I had a 1970s Ford 3/4 ton with a 4 speed manual. Same thing with it. Unless I was pulling our 12,000 lb cattle trailer. That truck with a 460 gas engine would never top 10 MPG empty. 5 MPG pulling a trailer. I don't miss it in the least. I wish they had a diesel engine back then.
I also understand BMW has gone to the "ZF" 8 speed A/T for 2012/2013 sans the 35 D ? I am sure BMW had its' reasons to use ZF 8 speeds.
Here are VW's
..."Due to the two additional gear levels, a 20 percent larger gearing spread can be attained between 1st and 8th gears. This accomplishes two objectives: First, thanks to this larger spread, the engines operate with even greater efficiency over all speed ranges, making them both more fuel efficient and responsive. Second, it was possible to lay out the 7th and 8th gears as speed-reducing gears (20 percent reduction) - fuel-saving overdrive gears."...
On the manual transmission side, even the 2001 Corvette Z06 uses 10% lower gears (probably 1 thru 4 gears) , even as it uses the 5/6 gears as "fuel savings/over drive gears. My sense is that 1 to 2 more gears would offer serious customer resistance and a number of other serious issues and bang for the buck inefficiencies, but that is purely a swag.
Don't think the X5d and VW TDI are good apples to apples on transmission efficiency. I only drove the TDI once several months ago, and it seemed quicker than the Q7 TDI, but the Q7 is definitely not in the X5d's league of quickness or engine responsiveness. The X5d is a tad quicker than the Touareg V8 Gen2 according to both Motorweek and my butt dyno. Not that I bought the X5d to drag race, but the higher hp (+25) and torque (+19) was apparent and may adversely impact maximum mpg compared to the Touareg. According to the guys in Spartanburg, the 8 speed BMW transmission in the other X5's was not a good match for the diesel low end torque, but it is likely that BMW will develop another/stronger 8 speed for future diesel applications. I believe the M diesels in Germany use an 8 speed (but they are designed to cruise at 130+ mph).
http://www.motorweek.org/reviews/road_tests/2008_volkswagen_touareg_2
http://www.motorweek.org/reviews/road_tests/2009_bmw_335d_2009_bmw_x5_xdrive35d
Again, issue isn't that in some/many applications that 8 is better than 6 gears in the transmission. It's just that this isn't a single variable equation that doesn't include other factors. I am pretty sure 20 gears is not 2.5 times better than 8 and in the case of a Tesla Model S, 1 forward gear works just fine. 0-60 in 3.9 seconds and the energy equivalent of about 100+ mpg. That's what a huge flat torque band will do. They decided against the previous 2 speed motor in the early Roadsters.
SIDEBAR:
(or for the way I have come to break in 3 TDI's, aka, slightly to moderately aggressively rpm NTE75- 80% @ less than 4,000 rpm on a 5,100 redline . Engine break in really continues to 30,000 miles to 50,000 miles. )
Truly I did not say that 20% gearing efficiencies translate directly to 20% BETTER mpg. However it does expand the range. Indeed it is a comparison range of 7.7 % (EPA H ratings) to 24%.(real world) (VARIANCE)
I am not sure why you ignore why even BMW has actually gone to an 8 speed (sans the diesel). So for example, IF you are saying an 8 speed vs a 6 speed have/yield NO differences, you would be wrong. That would be nonsensical and probably more costly for even BMW to switch ! ? If you are trying to say I am saying there is NO variance, you would be incorrect. Does higher or lower torque play a part? Absolutely. What does vary is how (YOU) use it in the conditions you drive. So really IF what you are saying is 425 # ft vs 406 # feet is the major variable eating up 2 mpg EPA H vs 19 each City ?... it doesn't track.
You are not saying the Tesla is a diesel? So if you are saying your BMW X5 35D had the Tesla transmission, you'd get all that power and 100 + mpg? I say lets leave the Tesla out of the discussion.
Now I am sure it is clear in your own mind what you said what you think you said, what you mean, what you assume I or anyone else should know, how anyone "TAKES" it. So in that sense I am asking is that what you really are saying? If not say it in an attempt to clarify. So if you want to leave it at YOU think the sky is Red and I think it blue, I am ok with that also.
Again, issue isn't that in some/many applications that 8 is better than 6 gears in the transmission. It's just that this isn't a single variable equation that doesn't include other factors.
Defacto even BMW (sans the X5 35 D) uses the 8 speed A/T (ZF vs Aisin). If that is a point ( nuance) too difficult to deal with, I say let's move on. Since most folks do not have 8 speeds A/T's, who cares?
But the combination is another reason why I do like diesels. I like diesels with DSG's. I am even ok with a diesel with a manual 5 speed. (I do wish it did come with a 6 speed)
Slow news diesel day: other than I recorded (from cable tv, and I am led to believe it is available off of Netflix) a 2009 episode of "How Its Made" (Audi) diesel engines (3.0 L) . Three other topics round out the episode: ski goggles, construction cranes, and porcelain figurines.
If one can see the piece on the (Audi Q7) engine component assembly, the graphics of the assembly process takes the mystery out of a sometimes vilified TDI.
As I have said in other posts, the (VW/Porsche/Audi) 3.0 L TDI engine depicted is a POWERFUL, reliable, durable, "bullet proof", efficient in many ways mainstay.
I would like to see one of the publications do a comparison of the SUV diesels offered in the USA. Here is a comparison by an owner of both the X5D and Touareg TDI.
http://www.clubtouareg.com/forums/f63/2013-touareg-tdi-vs-bmw-x5-diesel-80050.ht- ml
We currently have 4 diesel vehicles in our extended family: 2013 Cayenne (me), 2010 X5d (son), 2012 350 ML Bluetec (daughter) and 2012 Touareg TDI (sister / brother in law). I think that qualifies us as the most diesel family I know. The fact that all of these are different makes and models points primarily to the fact that everyone had different priorities. IMO, there are two "driver's" vehicles in that mix, the Cayenne and the X5d. And two comfort/luxury vehicles, the ML and the VW TDI. Comparing the VW TDI and the X5d is a little apples and oranges. Perhaps not for the majority of SUV purchasers, but certainly for someone who is inclined to look at the difference between 6 and 8 speed automatics as a serious engineering factor.
Interestingly, my Cayenne has an 8 speed that, although more fuel efficient, is not quite as responsive or quick as my sons X5d. The 8-speed Porsche tiptronic is designed to have a first gear that can get a 7,700 lb tow rolling, and a 7th and 8th gear that are for highly efficient highway cruising on level ground. My son's X5d, which I have driven extensively, simply has 6 gear ratios spaced out to get you to a highway cruising speed without a really tall overdrive. We live in the Pittsburgh area. Although it's too early to tell definitively, it appears that I get a bit better mileage than him, (2+/- mpg on highway). But with our somewhat hilly roads (PA Turnpike), I'd probably put the lighter weight (500+/- lbs?) as worth at least as much as the extra two gears.
I also happen to own a 2012 911S 7-speed manual. I can count on one hand the number of it's 4,500 miles that have been driven in 7th gear. Nice idea in theory, less so in practice. At least not in Pittsburgh area. Maybe on the Autobahn where 120+ mph cruising is possible, but not in the USA. It was a concession to the EPA.
Be that as it may, the oems in fact do and/or both try to differentiate their products, and at many different levels. To imply or state they do not, would simply be ignoring the truth. Perhaps the (your) caution comes from the fact there are very few diesels to compare with/against. So in that sense, it will always have apples to oranges to grapes flavor. Your post and the other realities confirms that.
Indeed while you only cite the Cayenne, the oem/s (VW family) tries to differential the products (also) even as the Cayenne, VW Touareg, Audi Q7 have the same base 3.0 V6 TDI and Aisin 8 speed A/T. An investigation of the engines and drive trains might reveal even FURTHER differentiated.They are truly not tied to the same computer tuning mapping, for example.
I would probably say the EPA's of both the 2013 Cayenne and your son's 2010 BMW X5 35D tell the real tale +/_ 2 mpg at least: EPA H of 28/26 mpg respectively. Perhaps at the same set of conditions and same mileages you would report the differences in mpg, as it is probably way too soon for your NEW Cayenne to be "reasonably" broken in.
They described the 7 speed A/T thusly:
..."and when the GL 350 reaches highway speeds, the transmission slips into a near catatonic double overdrive. At 80 mph, the engine is turning about 1,800 rpm (red line is 4,500 rpm)."...
Some other snippets: bp: $63,305, at: $99.840.
A relative (6 ft 2) sat in the rear of the VW Touareg and was literally glowing about how comfortable it was in the rear seating areas (500 miles+ R/T). One daughter even did a trip with us and I couldn't even get her to drive, so I could try out the rear cabin (1000+ miles R/T). Come to think of it, I couldn't get him to drive either.
1. 42 C / 49 H, 50 mpg average (179,000 miles)
2. 29 C / 40 H, 41 mpg average (47,000 miles)
3. 19 C / 28 H, 30 mpg average (15,000 miles)
A few (6) pretty boring impressions.
1. So far, the (3) VW's I have, meet at least one EPA number they have published.
2. In realities, the cars mpg averages have exceeded them by 2% to 7.1%, in the conditions they have been with 4 drivers.
3. The RANGES have been far better.
4. The averages could have been WAY higher, but it has been far more fun driving these cars slightly to moderately AGGRESSIVELY.
5. All in all for me, the diesels are way better adapted for the US roads I/we find myself/ourselves traveling.
6. Like model gassers post far less mpgs and percentages than diesels. 6b if I drove the gassers like I do the diesels the mpgs and percentages would be far less still.
..."VW AG's announcement on Friday that it would invest 50 billion (euros, my sic) ($65 billion us, my sic) in its global operations over the next three years marks the latest push from Germany's robust auto industry to limit its exposure to crisis-stricken Europe and widen its lead over the rest of the region's auto makers."...
German Car Makers Hit Road , pg. B3 WSJ Mon. Nov. 26, 2012 by Vanessa Fuhrmans, Christoph Rauwald, contributing.
Shorter term for VW (other oems are discussed), $1.3 B (us) for 2013-2015 to build Audi's first N/A plant in Mexico. $12.7 B (us) for 2013-2015 CHINESE jv's and for VW China's 5th factory in country.
There are gassers that also beat EPA estimates. I've shared at least 2 that I can recall in this thread.
My (04 Honda) gassers posts 38-42 mpg with an EPA of 29 C/38 H. I have followed Honda Civic threads and know what I/We get is higher than most.
But even in this case, there is not a US market "LIKE MODEL" turbo diesel Honda Civic 04 to compare it with/against.
I also follow VW Touareg gasser vs tdi. Most gasser VW T owners report 22 mpg. One (PUG) supercharged/hybrid VWT owner ( reports 24 mpg, not many and not on ). www.fueleconomy reports TDI @ 27.4 mpg. I have been getting 30 mpg. So percentage wise diesel posts 24.5% to 36.3% BETTER "LIKE MODEL" than gassers.
Now this is purely a SWAG on my part.
VW might have executed a Go game strategy with its upcoming VW Jetta turbo gasser/hybrid. Interestingly enough, it (the platform) competes against both the Corolla and Prius, gets slightly less mpg ( EPA H of 48 vs 45 or -6.25% less) than the Prius. Perhaps a more recognizable analogy is "killing "two birds with one stone". Yet the Jetta platform is a WAY better driving machine than either Corolla and/or Prius. It is also cheaper than a Prius and probably @ par with a tricked out Corolla.
Compared to things that suck, this other thing is good. Whoop-de-doo.
I look forward to seeing SkyActiv-D models come out, then hopefully we can compare modern/efficient gassers to their like model diesels.
Just checked out the 3 SkyActiv on the EPA site:
5 door auto: epa 32, actual 35
5 door man: epa 31, actual 38.3 (!)
4 door auto: epa 33, actual 35.5
4 door man: epa 31, actual 35.9
Very curious to see where the SkyActiv-D lands. There's less room for improvement, so they have their work cut out for them.
But clearly, moving FORWARD (the BO Potus admins (buzz light year) motto the 4 door family sedan Passat EPA H 32/Passat TDI EPA H of 43, Camry EPA H 35/Camry/Hybrid H 39 etc. are the new "ubiquitous". If the 2012 Passat TDI can do 84+ mpg, it makes one wonder what the Camry/Hybrid can do under same test methodologies. So far no answer.