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E82 / E88 1 Series (2008 - 2013)
BMWs throw back to the iconic 2002, with a renewed form and function. The smallest car in BMW's line up but still packs a punch. Available in coupe or convertible, powered by either an inline 6 in the 128 or the twin turbo rocket sled 135.

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  #1  
Old 03-08-2012, 05:34 AM
UltrasportA4 UltrasportA4 is offline
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135i Mileage Ratings

Just a quick question - why is the 7 speed DCT rated at 18/25, while the manual is 20/28? This seems like a very large gap compared to most cars. The new Audi S4's S-tronic transmission is more efficient than the manual..
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  #2  
Old 03-08-2012, 08:02 AM
Tom K. Tom K. is offline
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The quoted gear ratio specs for the 135i are very strange as BMWUSA shows a DCT (automatic) 3.46 final drive ratio with a 1 to 1 direct drive 7th gear.

http://www.bmwusa.com/Standard/Conte...fications.aspx

That would indicate something like 3,000 rpm @60 mph in top gear, but owners have reported it's closer to 2,100 - similar to the MT.

If the ratios are correct, the car is really geared low and would be hard pressed to achieve even 25 mpg.

Tom
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  #3  
Old 03-13-2012, 06:45 PM
one35i one35i is offline
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The overall gearing in the DCT is lower (numerically higher), this improves acceleration at the expense of fuel economy. BMW's DCT has no overdrive, 7th is 1:1, while on Audi's 7 speed S-Tronic, 5th is overdrive, 6th is double overdrive, and 7th is triple overdrive, making RPM's at highway speeds substantially lower. Here are Audi's gear ratios (anything smaller than 1:1 is an over driven ratio):

1st: 3.69
2nd: 2.24
3rd: 1.56
4th: 1.18
5th: 0.92
6th: 0.75
7th: 0.62

And BMW's DCT:

1st: 4.78
2nd: 3.06
3rd: 2.15
4th: 1.68
5th: 1.39
6th: 1.20
7th: 1.00

Last edited by one35i; 03-13-2012 at 06:53 PM. Reason: clarity
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  #4  
Old 03-17-2012, 09:51 AM
johnrose johnrose is offline
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Mr ONE that was an amazing reply.
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  #5  
Old 03-19-2012, 05:42 AM
BruceOmega BruceOmega is offline
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FWIW,

I was asking about the final drive ratio in this thread:
http://www.bimmerfest.com/forums/sho...al+drive+ratio

Answer I got was its an error on the web site. That number was the final drive ratio when the Steptronic was the AT option for the 135, but with the DCT its apparently 2.56:1.

I'm still curious about the gas mileage rating for the 135 with the DCT. Its notably lower than for the MT, and it a good bit lower than the new F30 3 series 335 with the 8-speed AT.

Thanks
Bruce
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  #6  
Old 03-19-2012, 11:28 AM
one35i one35i is offline
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While it appears to be true that the 135i's differential ratio is taller (numerically lower) than the web site suggests, I stand by my statement that 3 overdrives will markedly reduce engine RPM at highway speeds. The 135i's DCT is geared to accelerate as it's primary task.
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  #7  
Old 03-19-2012, 03:23 PM
Tom K. Tom K. is offline
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Quote:
Originally Posted by one35i View Post
While it appears to be true that the 135i's differential ratio is taller (numerically lower) than the web site suggests, I stand by my statement that 3 overdrives will markedly reduce engine RPM at highway speeds. The 135i's DCT is geared to accelerate as it's primary task.
OD or not is irrelevant. What counts is the overall ratio - gear x final drive. Having an OD (or 3 or 8) only reduces engine RPM when compared to the SAME FD ratio - otherwise it's apples & oranges. So without specifying the differential ratios, your figures are meaningless.

Incidentally, according to their US website, the current Audi A4 has three transmissions - one 6 speed manual and two 8 speed autos (Multitronic CVT and Tiptronic) but no S-Tronic. The Audi's overall ratios in 8th are higher (lower numerically) than BMW's DCT in 7th, but this is a function of total gearing, not simply having an OD or direct drive top gear.

http://models.audiusa.com/a4-sedan/d...specifications

Tom
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  #8  
Old 03-19-2012, 04:58 PM
one35i one35i is offline
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My original statement was an oversimplification of the gearing for the sake of brevity. You are correct that if the Audi has 9 inch diameter tires or an NHRA like 6:54 rear gear ratio, then 3 overdrives are "meaningless." However, I doubt either one is true.
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  #9  
Old 03-20-2012, 09:09 AM
Tom K. Tom K. is offline
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Quote:
Originally Posted by one35i View Post
My original statement was an oversimplification of the gearing for the sake of brevity. You are correct that if the Audi has 9 inch diameter tires or an NHRA like 6:54 rear gear ratio, then 3 overdrives are "meaningless." However, I doubt either one is true.
OK, next time provide the fd ratio (and tire size, if appliccable) and we'll do the math.

Of course, neither of us has explained why the MT 135i is rated at 28 highway versus 25 for the DCT - given that both turn about 2,100 RPM per mile in top gear.

Tom

Last edited by Tom K.; 03-20-2012 at 09:11 AM.
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  #10  
Old 03-20-2012, 11:28 AM
one35i one35i is offline
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Originally Posted by johnrose View Post
Mr ONE that was an amazing reply.
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  #11  
Old 03-20-2012, 08:59 PM
ProRail ProRail is offline
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Originally Posted by johnrose View Post
Mr ONE that was an amazing reply.
But very BORING. On this forum facts are the last thing we want. Opinions are MUCH more interesting, even if they are absurd.
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  #12  
Old 03-20-2012, 09:16 PM
one35i one35i is offline
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ProRail, I like your style!
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