# Dissappointing Fuel Economy



## lalitkanteti (Nov 15, 2009)

I too have separate Winter set (tyres-non RFT & rims). After changing to Summer RFT, I have noticed dip in my mileage but its not significant.


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## Flyingman (Sep 13, 2009)

Not sure what is up this tank but my mileage has dropped from a pretty steady 29-30mpg to about 26mpg. I did have a brutal commute one morning this week due to a car fire that closed an expressway. Major detour and delay.

It's warmed up here in the South so A/C is back on. I'll double check tire pressure.

Road trip coming up soon, so we will finally get some real highway miles.:thumbup:


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## Snipe656 (Oct 22, 2009)

My mileage as dropped a noticeable amount when stuck in bad traffic. I have been running into issues here lately with my mpg changing by 2-3 and think it is fuel quality but that is in my truck.


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## sdbrandon (Mar 18, 2006)

Tedj101 said:


> I bought my 2010 335d in late November. Since it came with the sports package and we were in Winter, I immediately put a set of Winter Performance tires on.
> 
> While my usage was initially mostly commuting, I did go on a couple of trips on the interstate and fuel mileage in all areas was about what I expected and pretty consistent with other users reports here and elsewhere.
> 
> ...


My guess is the first reading of 43.7 MPG was inaccurate. Did you measure manually dividing the gas used into the miles driven? Ignore onboard computers as they are rarely accurate.

The car is rated at about 35MPG hwy which is what you are getting so I see no issue. :dunno:


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## Snipe656 (Oct 22, 2009)

I figure out my mpg via my log and compare to the onboard reading with every fillup. This car has been pretty much exactly the same reading as my log, far from the difference he saw.


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## Chrisdridley (Jun 29, 2009)

When I changed from my Dunlop winter tires back to my Conti tires, I noticed a drop in mpg of about 1.8 - 2.0 
I have check the pressures again and they are correct but I am seeing this too......


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## Snipe656 (Oct 22, 2009)

So when you first swapped to winters you saw an increase in mpg?


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## Stugots (Jan 1, 2010)

Flyingman said:


> Not sure what is up this tank but my mileage has dropped from a pretty steady 29-30mpg to about 26mpg. I did have a brutal commute one morning this week due to a car fire that closed an expressway. Major detour and delay.
> 
> It's warmed up here in the South so A/C is back on. I'll double check tire pressure.
> 
> Road trip coming up soon, so we will finally get some real highway miles.:thumbup:


Since the car learns driving patterns, adjust shift patterns based on that, and does various other calculations throughout a drive, is it possible that the car gets confused when something that deviates from the norm (such as a 'poor' trip) and as such, that affects future tanks?

I mean...it's one big computer, right?


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## Snipe656 (Oct 22, 2009)

I think it is just because of the constant on/off the accelerator when in really bad traffic and nothing to do with computer confusion. Seems like it is the stop/go stuff that makes the economy on these things do a nose dive.


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## Tedj101 (Nov 24, 2009)

sdbrandon said:


> My guess is the first reading of 43.7 MPG was inaccurate. Did you measure manually dividing the gas used into the miles driven? Ignore onboard computers as they are rarely accurate.
> 
> The car is rated at about 35MPG hwy which is what you are getting so I see no issue. :dunno:


You have an interesting perspective - my data has to be wrong... I tried to give real figures and conditions to avoid just this sort of response. I thought I indicated that I suspected the computer wasn't working properly but the calculated data corroborated the computer. Oddly enough, I always check what I get with the computer with what I get based on fill ups (which is one of the reasons that I try to avoid using the nozzle adjustment tool) and mine is very very accurate (based on the miles reported by the odometer). Moreover, my Acura, my Dodge RAM and my Honda have computers that are pretty darned close (within a 10th or two) virtually all the time. Apparent inconsistencies from time to time are as likely to be due to imperfect filling procedures as they are to problems with the computer -- in my experience.

As to the 42.7 figure, it checked out at over 42 - after driving around at my friends house and the 125 mile return trip over the same roads. Moreover, it is not an uncommon figure for others on this forum. That is why I originally found it believable and was surprised to see it dissappear under the better conditions that pertain further South on 95.


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## Tedj101 (Nov 24, 2009)

Chrisdridley said:


> When I changed from my Dunlop winter tires back to my Conti tires, I noticed a drop in mpg of about 1.8 - 2.0
> I have check the pressures again and they are correct but I am seeing this too......


Just out of curiosity, do you have the sport package?


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## Chrisdridley (Jun 29, 2009)

Tedj101 said:


> Just out of curiosity, do you have the sport package?


No. I don't have the sport package on either of my 335d's. One thing I did notice is that each winter tire/wheel is 6 pounds lighter than my factory tire/wheel.....would 24 pounds of unsprung weight have this affect???? Some of you engineers chime in on this.


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